2.5l Jeep Tbi Diagnostic Download
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Apr 22, 2015 Moses Ludel’s 4WD Mechanix Magazine – Jeep TBI & MPI Advanced Troubleshooting Jeep How-to: Advanced Fuel-Injection Troubleshooting and Diagnostics On-board computers and self-diagnosis have been the most significant advancements in the automotive service field.
FUEL INJECTION SYSTEM - TBI
- OBD Scan Tools For ALDL or OBD1 car. In this page, we'll provide some information on how you can do that. But, before we go into that, there are some facts you need to know.
- Apr 22, 2015 Moses Ludel’s 4WD Mechanix Magazine – Jeep TBI & MPI Advanced Troubleshooting Jeep How-to: Advanced Fuel-Injection Troubleshooting and Diagnostics On-board computers and self-diagnosis have been the most significant advancements in the automotive service field.
- Workshop Repair and Service Manuals jeep All Models Free Online. Jeep Workshop Manuals. L4-150 2.5L VIN H TBI (1986) L4-150 2.5L VIN E TBI (1990) Wrangler. L6-4.0L VIN S (2000) L6-258 4.2L VIN M 2-bbl (1989).
- Diagnostic trouble codes may be cleared by disconnecting the battery ground cable for at least 20 seconds. Reconnect negative battery cable and recheck codes to confirm the repair. GM Specific Codes.
1988 Jeep Cherokee
1988 Electronic Fuel Injection JEEP/RENIX THROTTLE BODY INJECTION
2 . 5L Cherokee, Comanche, Wagoneer, Wrangler
DESCRIPTION
The Throttle Body Injection (TBI) system is a single injector system that introduces fuel into throttle body from above throttle plate. Fuel injector, located within throttle body, is controlled by the Electronic Control Unit (ECU).
The ECU is a sealed microprocessor that receives input signals from several sensors and other related engine components. Based on these inputs, ECU generates output signals that control and adjust air/fuel mixture and ignition timing as necessary for proper engine performance.
ECU also controls engine idle speed, emission control
systems, upshift indicator light (manual transmission only), and A/C compressor clutch.
OPERATION
ELECTRONIC CONTROL UNIT (ECU)
On Cherokee, Comanche and Wagoneer, ECU is located under instrument panel, above accelerator pedal. On Wrangler, ECU is located behind glove box. Input information from various engine sensors to ECU is used to determine engine operating conditions and needs. Battery voltage input is used to ensure that correct output voltage is supplied by ECU during fluctuations in battery voltage.
FUEL INJECTOR
Fuel injector is mounted in throttle body so that fuel is injected into incoming airflow. When injector solenoid is energized, armature and plunger move upward against spring. Check ball above injector nozzle moves off seat and opens small orifice at end of injector.
Fuel supplied to injector is forced around ball and through orifice, resulting in fine spray of fuel. Volume of fuel injected is dependent only on length of time that injector is energized by ECU, as fuel pressure is constant at injector. During cold engine starts, extra fuel is supplied so richer mixture will aid in starting.
FUEL PRESSURE REGULATOR
Fuel pressure regulator is integral part of throttle body. Pressure regulator has a spring chamber that is vented to same pressure as tip of injector. Because differential pressure between injector nozzle and spring chamber is same, only the length of time that injector is energized controls volume of fuel injected.
Fuel pump delivers more fuel than is required by engine. Excess fuel goes to fuel tank from pressure regulator via fuel return hose. Fuel pressure regulator function is mechanical and ECU does not control it.
FUEL PUMP
Electric roller type fuel pump is located in fuel tank. Integral check valve is used to maintain pressure in fuel delivery system after pump stops running. Fuel pump operation is controlled by ECU through a fuel pump relay.
IDLE SPEED ACTUATOR (ISA) MOTOR
ISA motor acts as movable idle stop to change throttle stop angle. Both engine idle speed and deceleration throttle stop angle are set by ISA. ECU controls ISA motor by providing appropriate voltage outputs to produce idle speed or throttle stop angle required for engine operating condition.
OXYGEN (O2) SENSOR
Oxygen sensor is equipped with a heating element that keeps sensor at proper operating temperature at all times. Oxygen sensor is located in exhaust pipe.
Maintaining proper sensor temperature at all times, system enters 'Closed Loop' operation sooner and remains in 'Closed Loop' during periods of extended idle. Electrical feed to oxygen sensor is through ignition switch.
The ECU receives sensor voltage signal which varies with oxygen content in exhaust gas. Signal is used by ECU as reference for setting air/fuel mixture ratio. ECU varies voltage to injector both to compensate for battery voltage fluctuations and to change duration of injector opening for control of air/fuel mixture.
MANIFOLD AIR/FUEL TEMPERATURE (MAT) SENSOR
MAT sensor provides a signal to ECU that changes depending upon temperature of air/fuel mixture in intake manifold. During high temperature conditions, ECU will compensate for changes in density of air.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
MAP sensor measures absolute pressure in intake manifold. Both mixture density and ambient barometric pressure are supplied to ECU by MAP sensor. Sensor is mounted in middle of firewall in engine compartment. Sensor receives manifold pressure information through vacuum line from throttle body. See Fig. 1.
Fig. 1: Manifold Absolute Pressure (MAP) Sensor Courtesy of Chrysler Motors.
COOLANT TEMPERATURE SENSOR (CTS)
Coolant temperature sensor is installed in intake manifold water jacket to provide coolant temperature input signal for ECU. During cold engine operation, ECU will make mixture richer, make up for fuel condensation in cold intake manifold, increase idle speed during warm-up period, increase ignition advance and keep EGR system inoperative until engine warms up.
THROTTLE POSITION SENSOR (TPS)
Throttle position sensor provides ECU with input signal, up to about 5 volts, to indicate throttle position. This allows ECU to control air/fuel mixture according to throttle position. TPS is mounted on throttle body assembly.
WIDE OPEN THROTTLE (WOT) SWITCH
WOT switch provides an input signal to ECU when engine is at wide open throttle. The ECU enriches air/fuel mixture. The WOT switch is located on the side of throttle body.
CLOSED THROTTLE (IDLE) SWITCH
Idle switch is integral with ISA motor and provides voltage signal to ECU. ECU will signal ISA motor to change throttle stop angle in response to engine operating conditions.
UPSHIFT INDICATOR LIGHT
On vehicles equipped with a manual transmission, ECU controls upshift indicator light. Indicator light is normally illuminated when ignition is turned on without engine running. Indicator light is turned off when engine is started.
Indicator light will be illuminated during engine operation in response to engine load and speed. If transmission is not shifted, ECU will turn light off after 3 to 5 seconds. A switch located on transmission prevents indicator light from being illuminated when transmission is shifted to highest gear.
ENGINE SPEED SENSOR
Engine speed sensor is attached to bellhousing. It senses and counts teeth on flywheel gear ring as they pass during engine operation. Signal from speed sensor provides ECU with engine speed and crankshaft angle. On flywheel gear ring, large trigger tooth and notch is located 90 degrees before each TDC point. Each trigger tooth is followed by 12 smaller teeth and notches before TDC point is reached.
As each of 12 small teeth and notches pass magnetic core in speed sensor, concentration and collapse of magnetic field induces slight voltage (spike) in sensor pick-up coil winding. See Fig. 2. Larger trigger teeth and notches induce higher voltage (spike) in sensor pick-up coil winding. These voltage spikes enable ECU to count teeth as they pass speed sensor.
Higher voltage spike (from larger tooth and notch) indicates to ECU that piston will be at TDC position after 12 smaller voltage spikes have been counted. ECU will then either advance or retard ignition timing depending upon remaining sensor inputs.
Fig. 2: Engine Speed Sensor Courtesy of Chrysler Motors.
A/C CONTROLS
ECU receives inputs from A/C when either A/C switch is in 'ON' position or compressor clutch engages to lower temperature. ECU changes engine idle speed depending upon A/C compressor operation.
POWER STEERING PRESSURE SWITCH
ECU receives input from pressure switch during periods of high pump load and low engine RPM. Input signals from pressure switch to ECU are routed through A/C request and A/C select input circuits. When pump pressure exceeds 250-300 psi (17.5-21.0 kg/cm), switch contacts close transmitting an input signal to ECU. ECU raises engine idle speed immediately after receiving input from pressure switch.
RELAYS
Starter Motor Relay
Starter motor relay provides an input signal to ECU when starter motor is engaged.
System Power Relay
System power relay, located on right fender inner panel, is energized when engine is started. It remains energized for 3 to 5 seconds after ignition is off. This allows ECU to extend ISA for next start before ECU shuts down.
Fuel Pump Control Relay
Fuel pump control relay is located on right fender inner panel. Battery voltage is supplied to relay from ignition switch. When ground is provided by ECU, relay becomes energized and provides voltage to fuel pump.
A/C Compressor Clutch Relay
ECU controls A/C compressor clutch through this relay. The A/C compressor clutch relay is located beside fuel pump control relay on right fender inner panel.
EGR Valve/Canister Purge Solenoid
Vacuum to both EGR valve and vapor canister is controlled by this solenoid. When solenoid is energized, neither EGR valve nor vapor canister receive vacuum.
Solenoid is energized during closed (idle) and wide open throttle operations, engine warm-up and rapid acceleration or deceleration. If solenoid wire connector is disconnected, both EGR valve and vapor canister will receive vacuum at all times.
Load Swap Relay
The load swap relay works in conjunction with power steering switch to disengage A/C compressor clutch. If compressor clutch is engaged when power steering pressure switch contacts close, input signal from switch to ECU also activates load swap relay. Relay then cuts off current to A/C compressor clutch.
The A/C compressor clutch remains disengaged until pressure switch contacts reopen and engine idle returns to normal. The load swap relay contains a timer that delays engaging the compressor clutch for 0.5 second to ensure smooth engagement.
ADJUSTMENTS
CAUTION: When working on or near engine that is running, be very careful to avoid pulleys, belts and fan. DO NOT stand in direct line with blades of fan. DO NOT wear clothing that is loose enough to get caught in moving parts.
IDLE SPEED ACTUATOR (ISA) MOTOR
Adjust ISA motor plunger to establish initial position of
plunger only if motor has been removed or replaced. Remove air filter
elbow and start engine. Run engine until engine reaches normal
operating temperature. Turn A/C off (if equipped).Connect tachometer leads to diagnostic connector D1,
attaching negative lead to terminal D1-3 and positive lead to
terminal D1-1. See Fig. 4. Turn ignition off. ISA motor plunger
should move to fully extended position.When ISA motor plunger is fully extended, disconnect ISA
motor wiring connector and start engine. Engine speed should be
3300-3700 RPM. If incorrect, turn hex head screw at end of plunger to
provide engine speed of 3500 RPM.Fully retract ISA motor by holding closed throttle (idle)
switch plunger inward as throttle is opened. Closed throttle switch
plunger should not touch throttle lever in closed position. If
contact is made, check linkage and/or cable for binding or damage.
Repair as necessary.Connect ISA motor wiring harness connector and turn
ignition off for 10 seconds. ISA motor should move to fully extended
position. Start engine. Engine speed should be 3500 RPM for short
period of time and then decrease to normal idle speed.Turn ignition off. Disconnect tachometer. After final
adjustment of ISA motor, use thread penetrating sealant (Loctite 290)
on adjustment screw to prevent movement and maintain adjustment.
NOTE: If adjustment screw must be moved after thread sealant
hardens, loosen threads by heating screw with flameless heat such as soldering gun. DO NOT use flame or torch type of heat as damage to ISA motor will result.
FUEL PRESSURE REGULATOR
WARNING: Always relieve residual fuel pressure in fuel delivery
system before opening system. To prevent chance of personal injury, cover fittings with shop towel while disconnecting fittings.
1) Replacement fuel pressure regulator must be adjusted to
establish correct pressure. Remove air filter elbow and hose. Connect
tachometer leads to diagnostic connector D1, attaching negative lead
to terminal D1-3 and positive lead to terminal D1-1. See Fig. 4.
Remove screw plug and install fuel pressure test fitting.
NOTE: Fuel pressure test fitting is not included with throttle body. Fitting (8983 501 572) must be obtained separately.
Connect fuel pressure gauge to test fitting. Start engine
and increase speed to approximately 2000 RPM. Turn Torx head screw at
bottom of regulator to set correct pressure. Turning screw inward
increases pressure and turning screw outward decreases pressure. See
Fig. 3.All models require fuel pressure of 14.5 psi (1.0 kg/cm).
Install lead sealing ball to cover regulator adjustment
screw after adjusting fuel pressure. Turn ignition off. Remove measuring equipment and test fitting. Install original plug screw and air filter assembly.
Fig. 3: Adjusting Fuel Pressure Regulator Courtesy of Chrysler Motors.
THROTTLE POSITION SENSOR (TPS)
1) Turn ignition on. Check throttle position sensor input
voltage. Connect voltmeter negative lead to terminal 'B' (M/T), or
terminal 'D' (A/T) of sensor connector. Connect voltmeter positive
lead to terminal 'C' (M/T), or terminal 'A' (A/T) of sensor connector.
NOTE: On (A/T) models, connector terminals are identified by
letters molded into back of connector. On all models, do not disconnect TPS harness connector. Insert voltmeter test leads through back of wire harness connector. On some models, it may be necessary to remove throttle body from intake manifold to gain access to sensor wire harness.
2) Move and hold throttle plate at wide open throttle
position (M/T), or close throttle plate completely (A/T). Ensure
throttle linkage contacts stop. Note voltmeter reading. Input voltage
at terminals 'B' and 'C' (M/T), or terminals 'A' and 'D' (A/T) should
be 5 volts.
Return throttle plate to closed throttle position (M/T),
or maintain throttle plate in closed position (A/T). Check sensor
output voltage. To do so, disconnect voltmeter positive lead from
terminal 'C' and connect it to terminal 'A' (top) of sensor (M/T), or
from terminal 'A' and connect it to terminal 'B' (A/T).Move and hold throttle plate in wide open throttle
position (M/T), or maintain throttle plate in closed position (A/T). Ensure throttle linkage contacts stop. Note voltmeter reading. Output voltage should be 4.6-4.7 volts (M/T), or .2 volt (A/T).
5) If output voltage is incorrect, loosen bottom sensor
retaining screw and pivot sensor in adjustment slot for a coarse
adjustment. Loosen top sensor retaining screw for fine adjustments.
Tighten screws after adjustment.
TESTING & TROUBLE SHOOTING
PRELIMINARY CHECKS & PRECAUTIONS
Subsystem Checks
Before testing fuel injection system for cause of
malfunction, check that following subsystems and components are in good operating condition:
Battery and charging system.
Engine state of tune.
Emission control devices.
Fuel system pressure and delivery volume.
Wiring connectors at components.
General Precautions
In order to prevent injury to operator or damage to system or component parts, use following techniques:
Turn ignition off before connecting or disconnecting any
component parts.DO NOT apply DC voltage greater than 12 volts or any AC voltage
to system.Disconnect battery cables before charging.
Remove ECU from vehicle if ambient temperature could exceed
176F(80C).DO NOT modify or circumvent any system functions.
RESISTANCE & VOLTAGE TESTS
MAT Sensor
Disconnect wiring from MAT sensor. Using high input
impedance digital volt-ohmmeter (DVOM), check resistance of sensor.
Resistance should be less than 1000 ohms when engine is warm. Replace
sensor if it does not fall within range shown in
TEMPERATURE-TO-RESISTANCE VALUES table.Test resistance in wiring harness between ECU connector
terminal No. 32 and sensor connector terminal. Also test resistance
in wiring harness between ECU harness terminal No. 14 and sensor
connector terminal. See Fig. 5. Repair wiring harness if open circuit
or resistance greater than one ohm is indicated.
Coolant Temperature Sensor (CTS)
1) Disconnect wiring harness from CTS. Using high input impedance digital volt-ohmmeter (DVOM), check resistance of sensor. Resistance should be less than 1000 ohms when engine is warm. Replace sensor if it does not fall within range shown in TEMPERATURE-to-RESISTANCE VALUES table.
2) Test resistance in wiring harness between ECU harn terminal No. 32 and sensor connector terminal. Also test resistance in wiring harness between ECU harness terminal No. 15 and sensor connector terminal. See Fig. 5. Repair wiring harness if open circuit or resistance greater than one ohm is indicated.
TEMPERATURE-TO-RESISTANCE VALUES (CTS & MAT SENSOR) TABLE
°F °C Ohms
(Approximate)
212 100 185
160 70 450
100 38 1600
70 20 3400
40 4 7500
20 -7 13,500
0 -18 25,000
-40 -40 100,700
Throttle Position Sensor (TPS) Test
Turn ignition on. Check voltage at terminal connector without disconnecting from TPS. Terminal 'A' (M/T), or terminal 'B' (A/T ) is output voltage, which should be 4.6-4.7 volts at wide open throttle (M/T), or .2 volt at closed throttle (A/T). Terminal 'B' (M/T), or terminal 'A' (A/T) is sensor ground. Terminal 'C' (M/T), or terminal 'D' (A/T) is input voltage, which is about 5 volts.
Closed Throttle (Idle) Switch Test
NOTE: ALL testing of idle switch must be done with ISA motor plunger in fully extended position. If switch cannot be tested without extending plunger, it is possible that ISA motor has failed. See IDLE SPEED ACTUATOR MOTOR ADJUSTMENT.
Turn ignition on. Check idle switch voltage at diagnostic
connector D2, between terminals No. 13 and 7. See Fig. 4. At closed
throttle, voltage should be near zero volts. When switch is off
closed throttle position, voltage reading should be greater than 2
volts.If voltage is always zero, test for short to ground in
harness or switch. Also check for open circuit between switch and
terminal No. 25 of ECU connector. If reading is always greater than 2
volts, check for open circuit in wiring harness between switch
connector and ECU. Also check for open between ground and switch
connector. Replace or repair wiring harness as necessary.
Manifold Absolute Pressure (MAP) Sensor Test
Check and repair vacuum hose connections at throttle body
and MAP sensor. Check output voltage at MAP sensor connector terminal
'B' (marked on sensor body) with ignition on, engine off. Voltage
reading should be 4-5 volts. If engine is hot and idling in Neutral,
reading should be 1.5-2.1 volts. Check voltage at terminal No. 33 of
ECU connector. Reading should be same as that at terminal 'B' on MAP
sensor connector. See Fig. 4.With ignition on, check MAP sensor supply voltage at
terminal 'C'. Reading should be 4.5-5.5 volts. Same voltage reading
should be obtained at terminal No. 16 on ECU harness connector. If
necessary, repair or replace wiring harness. Using Diagnostic Tester
(MS 1700), test ECU if necessary. Check MAP sensor ground circuit at terminal 'A' and terminal No. 17 of ECU connector. Repair wiring if necessary.
3) Using ohmmeter, check MAP sensor ground circuit between terminals No. 17 and 2 of ECU connector. If circuit is incomplete, check sensor ground connection on bellhousing, near starter motor. Replace ECU if ground is good. If terminal No. 17 is shorted to 12 volts, repair problem BEFORE ECU is replaced.
DIAGNOSTIC TOOLS
To properly test throttle body fuel injection system, service technician must have the following equipment available:
Digital volt-ohmmeter (DVOM) or volt-ohmmeter with minimum input
impedance of one megohm.12-volt test light, jumper wires and probes.
Hand vacuum pump with gauge.
Ignition timing light.
CONNECTOR D1
1.Tach{RPM) Input
Ignition
Ground
Starter Solenoid
Battery
Fuel Pump
CONNECTOR D2
1. Upshift Light (M/T)
2, System Power Relay
3- Park/Neutral Switch
System Power {Bait. Pos.)
A/C Clutch Relay
WOT Switch
Ground
Air/Fuel Temperature
M.P.A. (Ignition Output)
EGR/Canister Purge Solenoid
ISA Motor Extend {Forward)
Coolant Temperature Sensor
13- Closed Throttle Switch
ISA Motor Reverse
Automatic Transmission Diagnosis
Fig. 4: Jeep/Renix Fuel Injection Diagnostic Connectors Courtesy of Chrysler Motors.
DIAGNOSTIC TESTS
NOTE: When diagnosing fuel system problems using following
procedures, no specialized service equipment is needed. Following diagnostic procedures are NOT applicable if special tester M.S. 1700 is used.
Six different test flow charts are used to fully evaluate fuel injection system:
TEST 1: IGNITION OFF
This test checks that system power provides for ECU memory keep-alive voltage.
function.
TEST 2: IGNITION ON: POWER
This test checks system power function and fuel pump power
TEST 3 & 3A: IGNITION ON: INPUT
These tests check the following components and their circuits: closed throttle (idle) switch, Throttle Position Sensor (TPS), MAP sensor, A/T gear selector switch, Coolant Temperature Sensor (CTS) and MAT sensor. Coolant temperature and MAT sensors are tested in cold condition. This procedure also checks all interrelated wiring circuits as well.
TEST 4 & TEST 4A: SYSTEM OPERATIONAL
These tests check engine start-up circuit, fuel injector, 'Closed Loop' air/fuel mixture function, coolant temperature sensor function, MAT sensor function, detonation sensor 'Closed Loop' ignition retard/advance function, EGR valve and canister purge solenoid function, idle speed control and A/C control functions.
TEST 5: BASIC ENGINE
This test indicates failures in related engine components that are not part of fuel injection system.
TEST 6: MANUAL TRANSMISSION UPSHIFT
This test checks upshift indicator light function on vehicles with manual transmissions.
Ground
Ground
Ignition Switch
Battery
EGR Valve/Canister Purge
Fuel Pump Relay
System Power Relay
: 8- WOT Switch
9. Not Used
System Ground
Speed Sensor
Park/Neutral Switch (A/T)
TPS (Ground)
14 MAT Sensor
15. Coolant Temperature Sensor
16, MAP Sensor (Supply Voltage)
17 MAP Sensof (Ground)
IB Upshift Light (M/T)
19, System Power (Batt Pos.)
20. Not Used
21 Injector
A/C Compressor Clutch
ISA Motor Retract (Reverse)
ISA Motor Extend (Forward)
25 Closed Throttle (idle) Switch
Not Used
ignition Interference
Speed Sensor
Start Signal
A/C Select
Thmitle Position Sensor
Temperature Sensor Ground
MAP Sensor (Output Voltage)
A/C Request
Oxygen 0, Sensor Input
Tbi Diagnostic Tests
Fig. 5: Jeep/Renix Fuel Injection ECU Connector Courtesy of Chrysler Motors.
REMOVAL & INSTALLATION
COOLANT TEMPERATURE SENSOR (CTS)
Removal & Installation
Allow engine to cool down. Disconnect CTS wiring harness. Remove CTS from intake manifold and rapidly plug hole to prevent coolant loss. Install replacement CTS and connect CTS wiring harness.
FUEL INJECTOR
WARNING: Always relieve residual fuel pressure in fuel delivery
system before opening system. To prevent chance of personal injury, cover fittings with shop towel while disconnecting fittings.
Removal
Remove air cleaner assemby. Remove injector wiring connector. Remove injector retainer screws and clip. Using small pliers, carefully grasp center collar of injector between electrical terminals and carefully remove injector with lifting/twisting motion. Discard both 'O' rings. See Fig. 6.
Installation
Using light oil, lubricate new upper and lower 'O' rings.
Install 'O' rings in housing bore. Install back-up ring over upper
'O' ring. Position replacement injector in fuel body.Center nozzle in lower housing bore and use a
pushing/twisting motion to seat injector. Align wire connectors in proper orientation. Install retainer clip and screws. Connect injector wiring. Install air cleaner.
Throttle
Body
Fig. 6: Fuel Injector & Throttle Body Assembly Courtesy of Chrysler Motors.
FUEL PRESSURE REGULATOR
Removal & Installation
WARNING: Always relieve residual fuel pressure in fuel delivery
system before opening system. To prevent chance of personal injury, cover fittings with shop towel while disconnecting fittings.
With throttle body assembly removed, remove 3 screws holding fuel pressure regulator in throttle body. Remove fuel pressure regulator assembly. Note location of components for installation. Discard gaskets. To install, reverse removal procedure. Adjust regulator after installation. See ADJUSTMENTS in this article.
IDLE SPEED ACTUATOR (ISA) MOTOR
Removal & Installation
Disconnect throttle return spring. Disconnect wiring
harness connector from ISA motor. Remove ISA motor retaining nuts and
remove ISA motor from bracket.To install ISA motor assembly, reverse removal procedure.
Adjust ISA motor after installation. See ADJUSTMENTS in this article.
THROTTLE BODY ASSEMBLY
Removal
Remove air inlet duct and adapter plate. Remove throttle
cable and return spring. Disconnect electrical leads from fuel
injector, WOT switch, and ISA motor.Disconnect fuel supply and return lines at throttle body.
See Fig. 7. Tag and disconnect vacuum hoses. Disconnect TPS wiring.
Remove throttle body assembly. If throttle body assembly is being
replaced, transfer ISA motor and WOT switch bracket assembly to new
unit.
Installation
Fig. 7: Intake Manifold & Throttle Body Assembly Courtesy of Chrysler Motors.
THROTTLE POSITION SENSOR
Install replacement throttle body assembly on manifold using new gasket. Reconnect all hoses, wires and cable in reverse order of disassembly. Adjust ISA motor after installation. See ADJUSTMENTS in this article.
Removal & Installation
Remove throttle body assembly as previously described. Remove Torx head retaining screws. Remove throttle position sensor from throttle shaft lever. To install, reverse removal procedure. Adjust TPS after installation. See ADJUSTMENTS in this article.
MANIFOLD AIR/FUEL TEMPERATURE (MAT) SENSOR
Removal & Installation
Disconnect wire harness connector from MAT sensor. Remove MAT sensor from intake manifold. To install, reverse removal procedure. See Fig. 7.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
Removal & Installation
Disconnect wire harness connector, vacuum hose, and retaining nuts from MAP sensor. Remove sensor from firewall. To install, reverse removal procedure.
ELECTRONIC CONTROL UNIT (ECU)
Removal & Installation
On Wrangler, remove passenger assist handle and glove box
assembly. Remove ECU bracket retaining nuts from engine compartment
side of firewall. Disconnect ECU wiring harness. Remove ECU from
bracket. To install, reverse removal procedure.On all other models, remove retaining screws and bracket
that supports ECU above accelerator pedal. Remove ECU and disconnect
wiring harness. To install, reverse removal procedure.
EGR VALVE
Removal & Installation
Disconnect vacuum hose from EGR valve. Remove bolts which hold EGR valve to intake manifold. Remove valve and discard gasket. To install valve, reverse removal procedure. Always use new gasket. See Fig. 7.
TROUBLESHOOTING AND DIAGNOSIS
Fig.
36961
: TEST 1:
TEST1: IGNITION OFF
I
IGNITION OFF
TEST 2: IGNITION ON: POWER
Fig. 9:
36962
TEST 2:
CONTINUED ON NEXT GRAPHIC
IGNITION ON: POWER
CONTINUED FROM PREVIOUS GRAPHIC
Fig.
36963
10: TEST 2:
IGNITION ON: POWER (Cont.)
TEST 3: IGNITION ON: INPUT
Fig. 11:
36965
TEST 3:
CONTtNUED ON NEXT GRAPHIC
IGNITION ON: INPUT
CONTINUED FROM PREVIOUS GRAPHIC
Fig.
36966
12: TEST
3: IGNITION ON: INPUT (Cont.)
TEST 3: IGNITION ON: INPUT (Cont.)
I
CONTINUED ON NEXT GRAPHIC
36967
Fig. 13: TEST 3: IGNITION ON: INPUT (Cont.)
TEST ЗА: IGNITION ON: THROTTLE POSITION SENSOR
• DO MOT UNFASTEN THE SENSOR WIRE HARNESS CONNECTOR INSERT THE VOLTMETER TEST LEADS THAOUOH THE BACK OFTHE WIRE HARNESS CONNECTOR TQMAKE CONTACT WITH THE SENSOR TERMtNALS. ON SOME MODELS, IT MAY ALSO BE NECESSARY TO REMOVE THE THROTTLE BODY FROM THE INTAKE MANIFOLD. TO QAIN ACCESS TO THE SENSOR WIRE HARNESS CONNECTOR.
36971
Fig. 14: TEST 3A: IGNITION ON: THROTTLE POSITION SENSOR (M/T)
TEST 4: SYSTEM OPERATIONAL (Cont.)
36973
Fig. 15: TEST 4: SYSTEM OPERATIONAL
TEST 4A: SYSTEM OPERATIONAL
CONTINUED ON NEXT GRAPHIC
36974
Fig. 16: TEST 4: SYSTEM OPERATIONAL (Cont.)
CONTINUED FROM PREVIOUS GRAPHIC
CONTINUED ON NEXT GRAPHIC 36975
Fig. 17: TEST 4A: SYSTEM OPERATIONAL
CONTINUED FROM PREVIOUS GRAPHIC
36976
Fig. 18: TEST 4A: SYSTEM OPERATIONAL (Cont.)
CONTINUED FROM PREVIOUS GRAPHIC
CONTINUED ON NEXT GRAPHIC
36977
Fig. 19: TEST 4A: SYSTEM OPERATIONAL (Cont.)
CONTINUED FROM PREVIOUS GRAPHIC
CONTINUED ON NEXT GRAPHIC 36978
Fig. 20: TEST 4A: SYSTEM OPERATIONAL (Cont.)
CONTINUED FROM PREVIOUS GRAPHIC
Fig. 21:
36979
TEST 4A:
SYSTEM OPERATIONAL (Cont.)
TEST 4A: SYSTEM OPERATIONAL (Cont.)
CONTINUED ON NEXT GRAPHIC
36980
Fig. 22: TEST 4A: SYSTEM OPERATIONAL (Cont.)
TEST 5: BASIC ENGINE
36983
Fig. 23: TEST 5: BASIC ENGINE
TEST 6: MANUAL TRANSMISSION UP-SHI FT
i
Fig. 24:
CONTINUED ON NEXT GRAPHIC
TEST 6: MANUAL TRANSMISSION UPSHIFT
Fig. 25: Cherokee, Comanche & Wagoneer Throttle Body Fuel Injection System Wiring Diagram
Fig. 26: Wrangler Throttle Body Fuel Injection System Wiring Diagram
In 1986, the AMC 2.5L/150 four cylinder engine gained throttle body injection in the XJ Cherokee applications. This same engine in the Jeep CJ models still used a carburetor. The YJ Wrangler application of the 2.5L, introduced with the 1987 models, came with TBI, making this feisty engine the first use of fuel injection in a Jeep utility 4×4 model.
TBI is a bona fide electronic fuel-and-spark management system. While not as efficient or power-producing as multi-point fuel injection, TBI has all the off-highway and high-altitude benefits of electronic fuel-and-spark management. Constant feedback from sensors, electronic fuel delivery and spark timing, the TBI system provided cleaner emissions and improved drivability both on- and off-highway.
The 2.5L four with TBI was only offered from 1986-90. To serve the needs of pre-MPI YJ 2.5L owners, this article focuses on the components and potential trouble spots of the TBI system. Diagnostics involve computer interrogation and trouble codes from the TBI system, much like the MPI engines that follow in the 1991 2.5L and 4.0L designs. TBI also serves as a good introduction to EFI design and concepts.
Note—An orientation to basic TBI functions is useful for both TBI and MPI troubleshooting. Equipped with this knowledge, four-wheelers will have more confidence when leaving the paved highway for remote backcountry treks. This section provides Jeep owners with a basic understanding of electronic fuel injection.
The 1987 YJ Wrangler (shown) offers the first TBI engine in a utility Jeep 4×4 model. TBI has all of the benefits of a true EFI system. Fully electronic fuel-and-spark management eliminates the mechanical/vacuum advance ignition and a feedback carburetor. In its place is an Electronic Control Unit (ECU) that relies upon a host of engine sensors to adjust the ignition timing and fuel pulse width/flow in milliseconds. TBI provides optimal compensation for altitude, vehicle angles and throttle demands.
Right side engine view reveals a distributor, spark leads, a remote coil/ignition module (ICM) and the MAP sensor. The ignition system appears conventional. However, the ignition distributor no longer has mechanical or vacuum advance mechanisms. The distributor has no pickup, either. In this design, timing is controlled at the ECU computer. The ICM and coil send secondary (high) spark voltage to the distributor cap. The rotor distributes spark to each cylinder in the firing order: 1-3-4-2.
Routine service and troubleshooting of the distributor consists of confirming that the shaft turns properly and the cap/rotor components are in good condition. Like a conventional ignition, TBI 2.5L maintenance steps consist of spark plugs, spark plug wires, the distributor cap and rotor. Check for cracks, wear and corrosion at the cap and rotor contacts. Test spark wires and the coil lead for ohms resistance. Troubles beyond this will point to the ICM/coil, ECU or faulty sensor signals.
Setting Base Timing on the 2.5L TBI Four and the MPI Engines
While the ignition timing is fully controlled by the ECU and ICM systems, the distributor plays a critical role in delivering spark to each cylinder. For the TBI four and later MPI engines with a distributor, the distributor mounts in a fixed position and does nothing more than “distribute” spark to each of the cylinders in the firing order. The ECU computer or PCM knows the piston positions from the crankshaft position sensor (CPS) signal at the flywheel.
Setting fixed timing requires a one-time location of the distributor. On a TBI or MPI Wrangler engine, you cannot adjust spark timing by moving the distributor housing! Timing is a programmed function of the ECU or PCM computer—not the distributor. 2.5L MPI and 4.0L MPI engines locate the rotor in a different position than the TBI distributor depicted in this section. (See ‘Note’ below for MPI timing details.)
Note—On 1991-up MPI engines, the 2.5L distributor’s rotor faces slightly past 3 o’clock when aligned with #1 cylinder’s spark wire lead—not 6 o’clock as with the 1986-90 2.5L TBI engines. Start the 2.5L MPI distributor with the oil pump tang near 10 o’clock to place the rotor at slightly past 3 o’clock with the distributor housing seated. On MPI 4.0L engines, align the oil pump tang near 11 o’clock to place the distributor rotor at 5 o’clock with the distributor housing seated. All settings reflect #1 piston at TDC on its compression stroke.
To index or position the distributor properly, begin by making sure that #1 piston is rising on its compression stroke. Ignition OFF and coil wire detached for safety sake, you can remove the #1 spark plug if necessary to note the cylinder pressure as the piston rises on this stroke. Rotate the crankshaft with a hand wrench, bringing the damper mark just to the TDC (0-degree position) in the normal direction of rotation. In the steps shown here, I share the one-time, required setting of the distributor. You can use this procedure at your shop or in a field emergency.
Here, I have aligned the “0” degree mark with the crankshaft pulley’s damper notch for TDC on #1 piston. (If necessary, remove the #1 spark plug and feel for pressure to confirm that the piston for #1 cylinder is reaching the top of its compression stroke and not the exhaust stroke.) As shown, the #1 piston is at the top of its firing stroke or top-dead-center (TDC).
The distributor has an additional and very important role: driving the oil pump! At the base of the distributor shaft, there is a tang that fits into the slot at the top of the oil pump drive shaft. Since the camshaft’s drive gear and distributor’s driven gear are helically cut, the distributor shaft will turn as the distributor drops into position and engages the oil pump drive. For 2.5L TBI fours, the oil pump drive should be aligned at slightly past 3 o’clock for the distributor to end up with the rotor facing 6 o’clock. Install a new distributor housing-to-block base gasket or O-ring as required.
If the oil pump drive and distributor tang align during fitment, the rotor will wind up facing 6 o’clock—correct for the 1987-90 2.5L TBI fours. If the rotor does not face 6 o’clock as shown, the distributor must be lifted up and the oil pump drive realigned with a screwdriver. Try again, with the distributor tang engaging the pump drive slot near 3 o’clock then rotating to place the rotor blade at 6 o’clock with the distributor housing fully seated. Make certain the housing seats flush with the bolt slot aligned correctly. Torque the clamp bolt to 17 ft-lbs.
Note—On MPI 2.5L engines, the rotor blade should face slightly past 3 o’clock when the distributor seats. An MPI 4.0L’s rotor blade should face 5 o’clock with the distributor housing seated. This requires an oil pump drive alignment near 10 o’clock for 2.5L MPI fours and near 11 o’clock for 4.0L MPI sixes. When installed right, the rotor will face the correct clock position with the distributor housing’s bolt notch aligned with the engine block bolt hole. All references are with #1 piston at TDC on its compression stroke. Torque the clamp bolt to 17 ft-lbs.
Here, the distributor housing locating tab is clearly in place. This distributor will only fit in one position. With #1 piston at TDC on its compression stroke, and with the rotor facing 6 o’clock, you can secure the hold-down hardware to 17 ft-lbs torque. The spark plug wires will go in place, with #1 lead at the 5 o’clock distributor cap position and the other three leads placed clockwise in the firing order: 1-3-4-2. The center tower of the distributor cap accepts the ICM/coil lead. Seat spark wires securely.
Note—For 2.5L and 2.4L engines, the cylinders number 1-2-3-4 from front to rear. 4.2L and 4.0L engines number 1-2-3-4-5-6 from front to rear.
EFI/TBI systems depend upon a strong signal from the engine speed sensor. The sensor calculates TDC by reading a trigger tooth on the flywheel or flexplate. This Crankshaft Position Sensor (CPS) is common to 2.5L and 4.0L engines. Mounted at the left upper section of the flywheel/converter housing, the CPS is vulnerable to dust, dirt and oil. At high mileage, as oil accumulates on the flywheel or flexplate, the sensor may fault. Simply removing and cleaning the device can often restore performance and eliminate hard engine starts.
Flywheel or drive plate has notch teeth. The CPS has a magnetic probe that finds the gap in this set of teeth. 12 teeth later, a reference piston reaches TDC (top-dead-center). The ECU uses this reference and sensor input for firing mixtures and setting the ignition spark advance and retard. This is a highly accurate system that can adjust timing in milliseconds. Spark to plug wires reflects ever-changing ICM signals and coil triggers.
Note—The manual clutch flywheel or automatic transmission drive plate is somewhat inaccessible for cleaning. If the rear main seal leaks on a 2.5L or 4.0L engine with a CPS, fix the main seal leak to eliminate risk of chronic oil contamination of the speed sensor, which will produce hard starting and no starts. You can test the 2.5L TBI engine’s CPS across its ‘A’ and ‘B’ terminals with the engine hot, shut off and the connector loosened: Quick diagnostic readings should be 200 plus-or-minus 75 ohms.
TBI electronic fuel-and-spark management uses an ignition control module (ICM) that interfaces with the ECU. Ignition spark advance and retard each rely upon a signal from the ECU to the ICM. The ICM output is simple enough, with just a tachometer lead and a high voltage spark wire lead from the coil to the distributor cap high tension tower (center post). Fortunately, if the coil is defective, this is an item that can be serviced separately and does not require replacement of the entire ICM.
The ECU (electronic control unit) mounts above the heater assembly on this early YJ with 2.5L TBI. This ECU uses a “35-Pin” type plug harness. The ECU controls spark output and timing once the distributor base timing is correct. Signals from the coolant temperature sensor (CTS), tachometer (ICM signal), manifold air temperature (MAT) and manifold absolute pressure (MAP) tell the ECU how much timing advance is needed. When spark timing is incorrect and if the ECU, ICM and distributor all check okay, the CTS, MAT or MAP sensor could be at fault.
The coolant temperature sensor (CTS) threads into the intake manifold’s coolant port. CTS signals affect spark timing and cold-start performance. This device sends a voltage signal to the ECU that helps determine the injector pulse width (fuel flow volume), cold/warm-up idle speed, spark advance when coolant is cold plus the exhaust gas recirculation (EGR) valve function. If the cold-start system is quirky, check the wire integrity and ohms resistance of the CTS. Resistance across the CTS wires should be less than 1000 ohms with a warm engine.
Note—In the photo above, the wires are bare at the switch. If ohms check okay and the wires are still strong, consider coatings of Liquid Electrical Tape to re-insulate and seal these wires. This product can restore costly electrical devices that have damaged insulation.
The manifold air temperature (MAT) sensor threads into the intake manifold. This signal indicates the air/fuel temperature in the intake manifold. Nissan tiida workshop manual free download. The resistance should read less than 1000 ohms with the engine warmed to normal operating temperature. Check resistance between the two MAT sensor plug contacts. Though not as accurate as a mass-air flow sensor, the MAT signal proves valuable in helping the ECU set proper fuel flow and spark timing under various engine and atmospheric conditions.
The MAP sensor mounts against the firewall and reads manifold pressure. At connector terminal ‘B,’ with the ignition switch ON and engine not running, voltage should read 4-5 volts. This reading should drop 1.5-2.1 volts on a hot engine idling without a load in neutral or Park. Supply voltage from the ECU harness, read at terminal ‘C’ of the MAP sensor, should be 5 volts plus-or-minus 0.5-volts with the ignition ON. If out of range on voltage readings, replace the MAP sensor.
The throttle body has fewer parts than a carburetor and is easy to disassemble and rebuild. Little trouble occurs unless fuel is contaminated or air and fuel filtration is poor. Routine service is simply installing new OE-type filters. If there is a pressure regulator problem, the pressure regulator fits within the bowl beneath the fuel inlet. When servicing the pressure regulator, you check pressure at the test port. A running TBI engine will have 14-15 psi.
Note—Excessively high pressure readings indicate a possible pinched fuel return line. Pressure regulator adjustments are usually minute and only to correct minor changes in the regulator and system over time. When there is not enough pressure, even after attempts to increase pressure at the regulator’s adjuster, there is either a restricted fuel supply system or a low output electric fuel pump in the fuel tank.
This is the fuel injector. Before removing the injector, check its spray pattern. If okay, leave the injector alone. To remove the injector, release its wiring leads and connector as an assembly. Grip the center collar of the injector with small channel lock pliers and rock the unit sideways; the injector pulls straight upward. A lock tab secures the base of the injector. Never attempt to twist the injector loose, which would damage the unit. Replace worn centering and O-type rings with fuel-rated new rings.
Years ago, I performed a good deal of work on TBI truck engines. A neat trick for testing injector performance is to hook your induction timing light to a spark plug lead. Run the engine with the light aimed at the injector and down the throttle body throat. A clean injector with normal pulse widths shows a uniform, conical fuel spray pattern. This is a quick check for poor flowing or clogged TBI injectors.
Note—If you cannot get a pattern at a given spark lead, try each of the four leads. A poor or absent fuel spray pattern is easy to discover this way. Be aware that a flooded engine will not flow fuel once the oxygen sensor signals the presence of raw, unburned fuel. Let the engine stand for a while before testing for fuel flow.
The throttle position sensor (TPS) sends the ECU constant data about the throttle opening and driver’s demands. A correct TPS setting puts the output/input voltage ratio in the 0.925-0.935 range. This is calculated by dividing the input voltage to the TPS into the output voltage reading. Output voltage should be 93% of input voltage. For this test, the ISA plunger must retract away from the throttle arm. The throttle should be in its idle stop position (fully retracted).
This is the Idle Speed Actuator (ISA) for the 2.5L TBI engine. A special exerciser tool is used to fully extend the ISA plunger. Fully extended, the plunger should bring an unloaded engine to 3500 rpm. This is a high rpm for a stationary engine, and I advise removal of the fan belt(s) for this brief test and adjustments. Before performing this test, the A/C should be off, the throttle body intake bonnet removed and the engine fully warmed. Use an accurate tachometer to pinpoint 3,500 (crankshaft) rpm.
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Note—During the 2.5L TBI era, the “Ele. AB.99” tool was a Jeep dealership service device for exercising these ISA units. Make sure the plunger extends fully when performing this test. Set speed only with the ISA plunger fully extended. Do not run an unloaded engine at this speed for long—simply confirm the rpm.
Testing and Calculating ‘TPS’ Voltage
The voltage input for the TPS is typically in the 5-volt range. Output voltage to meet the idle-stop ratio of 0.93:1 or 93% is checked and adjusted with the ignition switch in the ON position and the 2.5L TBI engine not running:
1) Determine input voltage by first setting your voltmeter for 12-volt DC readings. At the TPS terminals A, B and C, insert the negative (-) lead into the backside of terminal B. Insert the positive (+) lead into the backside of the C terminal. You should get a reading around 5-volts. Use the hundredths of a volt scale.
2) Now move the positive (+) voltmeter lead to the A terminal. Read the output voltage.
3) Divide the input voltage reading into the output voltage. A figure of 0.925-0.935 should result. 0.930 is optimal for a TPS switch with the throttle against its stop position and the ISA plunger tip not contacting the throttle arm.
4) You can adjust the TPS switch carefully to obtain the correct output voltage. If the specification is not attainable, replace the switch.
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Note—The ISA motor can be retracted by use of a special exerciser tool. TPS voltage adjustments can be made using a special tester, the dealership recommended DRB-II® or DRB-III®. If you do not have these devices, the ISA motor is removable for this test; an accurate voltmeter test, as described above, provides a reasonable alternative. Reinstall the ISA motor in its original position after setting the TPS.
The EGR canister purge valve is a solenoid controlled by the ECU. The valve applies and shuts off vacuum to the EGR valve and the Evaporative Canister. The solenoid prevents the EGR and canister from operating during the engine warm-up mode, at an idle, during wide open throttle and during quick acceleration and deceleration. If you disconnect this solenoid, the EGR and evaporative canister will operate at all times, causing rough running and hazardous vapor conditions.
The wide-open throttle (WOT) switch should look familiar. A similar device was used on BBD carburetors. WOT switch activation will cause the ECU to ground the EGR/Evaporative Canister solenoid, cutting off vacuum to these devices to prevent their operation during full-throttle mode. Activation of the WOT switch also signals the ECU to ignore the oxygen sensor and allow the TBI injector to flow a pre-set amount of extra fuel.
This is the oxygen (O2) sensor (at right) used with the 2.5L TBI engine. It is an electrically heated unit located at the base of the cast exhaust manifold near the header pipe. The benefit of a heated O2 sensor is quicker closed-loop functions during engine warm-up and stable performance during extended periods of idling. By reading the oxygen content in the exhaust, the O2 sensor provides the ECU with vital, continually changing information about the air-fuel ratio. The ECU adjusts fuel flow to provide optimal performance and low tailpipe emissions.
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Do not attempt to disconnect fuel lines without these tools! Pipes will separate quickly and easily with the right tool. This is a Lisle product purchased at a Sears retail store. Various sizes fit fuel and common A/C couplers. Whether you are servicing the fuel filter, removing the engine or changing fuel lines, these spring release devices can prove essential. Coupler repair kits are available from Mopar/Jeep.
The EGR valve has been popular since the mid-1970s. Exhaust gas recirculation under specific conditions will reduce oxides of nitrogen, the main cause of visible pollution. As a certified emissions mechanic, I learned the value of the EGR and some of its ancillary benefits—mainly its ability to lower the upper cylinder temperatures to below 2500-degrees F. The EGR is lifesaving for engines and valuable for the environment. Always make certain the EGR valve functions properly. You can test this valve with a vacuum hand pump.
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The positive crankcase ventilation valve (PCV) is a routine service item. This simple device helps purge the crankcase of toxic and damaging fumes. While part of a closed crankcase emissions system, the PCV valve does require replacement at normal intervals. If stuck open, the PCV will create a nuisance vacuum leak. If clogged or stuck closed, the PCV can allow excessive crankcase pressure and even create crankshaft seal or engine gasket leaks. I replace the PCV valve at 30,000 mile intervals.