Engine Controls - System/component Tests - 2.5L: Diagnosis Jeep Cherokee II

CLOSED THROTTLE (IDLE) SWITCH TEST

Note. Testing must be done with Idle Speed Actuator (ISA) motor plunger in fully extended position as after normal engine shutdown. See IDLE SPEED under FUEL SYSTEM in this article.

Scheme 255

1. Shut off engine and note if ISA motor plunger extends. If necessary to extend plunger for test, an ISA motor failure can be suspected. Adjust ISA motor if necessary. With ignition switch in ON position, test switch voltage at diagnostic connectors D2-13 and D2-7 (ground). (Scheme 255)
2. Voltage should be close to zero at closed throttle and greater than 2 volts when throttle is not closed. If no voltage is present in either position, test for short circuit to ground in wire harness or switch. Test for open circuit between ECU connector terminal No. 25 and switch.
3. If voltage is always more than 2 volts, test for open circuit in wire harness between ECU and switch connector, and between switch connector and ground. Repair or replace wire harness as necessary.

Scheme 256

Scheme 257

Scheme 258

RESISTANCE TEST

1. Disconnect wire harness connector from CTS. Test resistance of sensor with DVOM. Resistance should be less than 1000 ohms with engine warm. Replace sensor if not within range of resistance specified in chart. See «TEMPERATURE-TO-RESISTANCE VALUES»(ref-24457-S17249988252001010500000) table.
2. Test resistance of wire harness between ECU harness connector terminal No. 15 and sensor connector terminal, and terminal No. 32 to sensor connector terminal. see scheme 1and see scheme 2. Repair wire harness if open circuit is indicated.

Disconnect speed sensor connector from harness. Place ohmmeter across terminals "A" and "B" (marked on connector). Reading should be 125-275 ohms (hot engine). Replace sensor if readings are not within specification.

FUNCTIONAL TEST

1. Connect DRB-II to vehicle and proceed to state display mode. Start engine and observe knock unit value. Using tip of screwdriver, gently tap cylinder block near knock sensor and observe knock value. Knock value should increase while tapping on cylinder block.
2. If knock value does not increase while tapping on the cylinder block near knock sensor, check knock sensor for proper connection. If connection is good, replace knock sensor.

1. Inspect Manifold Absolute Pressure (MAP) sensor vacuum hose connections at throttle body and sensor. Repair as necessary. Test MAP sensor output voltage at MAP sensor connector terminal "B" (as marked on sensor body) with ignition on and engine off. Output voltage should be 4-5 volts. Voltage should drop to 1.5-2.1 volts with a hot, neutral idle condition.
2. Test ECU terminal No. 33 for the same voltage as above to verify wire harness condition. Repair as necessary. Test MAP sensor supply voltage at sensor connector terminal "C" with ignition on. The voltage should be 4.5-5.5 volts. Same voltage should also be at terminal No. 16 of ECU wire harness connector. Repair or replace wire harness as necessary.
3. Test MAP sensor ground circuit at sensor connector terminal "A" and ECU connector terminal No. 17. see scheme 1or see scheme 2. Repair wire harness as necessary. Test MAP sensor ground circuit at ECU connector between terminal No. 17 and terminal No. 2 with ohmmeter.
4. If ohmmeter indicates an open circuit, inspect for defective sensor ground connection on flywheel/drive plate housing near starter motor. If ground connection is good, replace ECU. If terminal No. 17 has a short circuit to 12 volts, correct condition before replacing ECU.

1. Disconnect wire harness connector from Manifold Air/Fuel Temperature (MAT) sensor. Test resistance of sensor with DVOM. Resistance should be less than 1000 ohms with engine warm. Replace sensor if not within range of resistance specified in chart. See the «TEMPERATURE-TO-RESISTANCE VALUES»(ref-24457-S17249988252001010500000) table.
2. Test resistance of wire harness between ECU harness connector terminal No. 32 and sensor connector terminal, and terminal No. 14 to sensor connector terminal. see scheme 1or see scheme 2. Repair wire harness as necessary if resistance is greater than one ohm.

TEMPERATURE-TO-RESISTANCE VALUES

RESISTANCE TEST (CHEROKEE & COMANCHE)

Disconnect O2 sensor connector. Connect ohmmeter test leads to connector terminals "A" and "C" of sensor connector. Resistance should be 5-7 ohms. Replace sensor if ohmmeter displays an infinity reading.

RESISTANCE TEST (WRANGLER)

Disconnect O2 sensor connector. Connect ohmmeter test leads to connector terminals "A" and "B" of sensor connector. Resistance should be 5-7 ohms. Replace sensor if ohmmeter displays an infinity reading.

1. Disconnect wire connector at TPS. Check voltage at TPS connector pins "B" (ground) and "C" (5 volt supply) with key on. If there is not approximately 5 volts, turn key off. Check for continuity between ECU connector pin No. 16 and TPS connector terminal "C".
2. If there is an open circuit, repair TPS wire harness power supply circuit between ECU and TPS and retest. If there is no open circuit, check for continuity between ECU connector pin No. 13 and pin "B" of TPS connector. If there is an open circuit, repair TPS wire harness ground circuit between ECU and TPS and retest.
3. If there is no open circuit, check for continuity between ECU connector pin No. 31 and TPS connector pin "A". If there is an open circuit, repair TPS wire harness between ECU and TPS and retest. If there is no open circuit, replace ECU and retest. NOTE: DO NOT disconnect sensor wire harness connector. Insert voltmeter test leads through back of wire harness connector to make contact with sensor terminals. On some models, it may be necessary to remove throttle body from intake manifold to gain access to sensor wire.
4. With wire connector still disconnected at TPS. Check voltage at TPS connector pins "B" (ground) and "C" (5 volt supply) with key on. If there is approximately 5 volts, connect TPS wire connector to TPS. Check voltage at TPS connector terminals "A" (+) and "B" (ground) with key on and throttle plate wide open.
5. If output voltage is 4.6-4.7 volts, TPS switch and adjustment are okay. If voltage is not correct, adjust voltage to specification. If voltage can be adjusted to 4.6-4.7 volts at WOT, TPS and wiring are okay. If voltage cannot be adjusted to specification, replace TPS and adjust voltage.

FUNCTIONAL TEST (WRANGLER)

1. Disconnect wire harness connector from WOT switch. Test on-off function of WOT switch with DVOM several times while manually opening and closing throttle valve. Resistance should be infinite with throttle closed and have a low resistance when wide open. Replace switch if defective.
2. Connect wire harness connector. With ignition on and engine not running, connect voltmeter across diagnostic connectors D2-6 and D2-7 (ground). (Scheme 255) There should be no voltage reading when throttle valve is at WOT position. Voltage should be greater than 2 volts when throttle is not at WOT position.
3. If no voltage is present in either position, test for a short circuit to ground in wire harness or switch. Check for open circuit between ECU connector terminal No. 8 and switch connector. Repair or replace wire harness as necessary. If voltage is always greater than 2 volts, test for open circuit in wire or connector between switch and ground. Repair as necessary.

IDLE SPEED TEST

Note. The following test must be performed using ISA Exerciser (7088). If ISA motor is tested off vehicle, ISA motor shaft must be lightly preloaded to avoid jamming during test. Use light finger pressure to preload ISA motor shaft and simulate throttle return pressure.

IDLE SPEED ACTUATOR (ISA) MOTOR TEST

1. Ensure rubber boot is correctly positioned in its groove on ISA motor shaft. If boot is not correctly positioned, correct its position and recheck vehicle for proper idle. If boot is correctly positioned, continue diagnosis procedure. Open throttle and attempt to extend and retract ISA motor by pulling and pushing axially (in and out) on the ISA shaft. CAUTION: If shaft axial movement is more than 3/8" (9.53 mm), do not continue. Replace ISA motor.
2. Ensure ignition is off. Connect ISA Exerciser (7088) power leads to vehicle battery (red to positive, black to negative). Disconnect ISA motor connector. Connect ISA Exerciser (7008) 4-pin connector to ISA motor connector. It may be necessary to slot casing of one of the exerciser pins to connect exerciser to ISA motor.
3. Examine motor shaft tip position. Tip should be in contact with throttle lever and throttle should be partially open. If tip is not in contact with throttle lever and throttle lever is closed, ISA motor is fully retracted and jammed. Go to step 4) to unjam motor. If desired results were obtained, skip step 4) and go to step 5).
4. Apply parking brake. Start engine. With engine running, open throttle to 1500 RPM and move exerciser switch in EXTEND direction several times to unjam ISA. Motor tip should be in contact with throttle lever. Throttle should be partially open. If motor shaft tip is not in contact with throttle lever and throttle is still closed, motor is permanently jammed. Stop procedure and replace ISA motor. If desired results were obtained, ISA motor is unjammed. Go to step 5).
5. Move exerciser switch in EXTEND direction for 5 seconds. Watch ISA motor action. ISA motor should ratchet (click) several times when it reaches fully extended position. If motor does not ratchet, replace ISA motor. If motor ratchets, ISA motor is okay. Go to next step.
6. Move exerciser switch to RETRACT direction for 5 seconds. Watch ISA motor action. ISA motor should close throttle and stop automatically in three seconds. Closed throttle switch light on exerciser will go out when ISA motor reaches closed throttle position. Tip of actuator should be in contact with, or be no more than 0.20" (0.50mm) away from, throttle lever when ISA motor has stopped movement. Throttle lever should also be in contact with throttle stop screw on main body of throttle body when ISA motor movement has stopped.
7. If ISA motor does not move, stop procedure and replace ISA motor. If motor closed throttle, but retracted away from throttle lever and was no longer in contact with lever, ISA motor is defective. Stop procedure and replace ISA motor. If ISA motor moved throttle, but throttle was not in contact with closed throttle stop screw on TBI main body when ISA motor stopped movement, go to step 8). If desired results were obtained, skip step 8) and go to step 9).
8. Push throttle in closed direction while pressing exerciser switch in RETRACT direction for 5 seconds. ISA motor should continue to retract until throttle lever contacts with closed throttle stop screw on throttle body main body. If desired results were obtained, ISA motor is okay. Check throttle control system for freedom and smoothness of movement. Inspect throttle return springs. Repair as necessary. After repair, go to step 9). If ISA motor did not move, stop procedure and replace ISA motor.
9. With exerciser, move ISA motor in EXTEND and RETRACT direction 2 or 3 times. When stopping, always leave ISA motor extended. ISA motor should operate smoothly and ratchet at end of EXTEND travel. It should stop automatically at end of RETRACT travel. If movement is intermittent, slow, or "gritty" sounding, replace ISA motor. If desired results are obtained, ISA motor is okay. If an idle problem still exists, refer to BASIC TESTING article. Remove Exerciser Tool (7008) and reconnect ISA motor.

1. Insert positive voltmeter lead into Blue wire at distributor connector. Install negative lead into Gray wire with tracer at distributor connector. Set voltmeter on 15 Volt A/C scale. Turn ignition on.
2. Voltmeter should show approximately 5.0 volts. If there is no voltage, check leads for good connection. If there is still no voltage, remove ECU and check for voltage at pin C-16 with harness connected.
3. If there is still no voltage, perform vehicle test using DRB-II. If voltage is present, check continuity between Blue wire at distributor connector and pin C-16 at ECU. If there is no continuity, repair harness as necessary. Check for continuity between Gray wire with tracer at distributor connector and pin C-5 at ECU. If there is no continuity, repair harness as necessary. Check continuity between Black wire at distributor connector and ground. If there is no continuity, repair harness as necessary.
4. Set voltmeter to low AC scale. While observing voltmeter, crank engine. Voltmeter needle should fluctuate back and forth while engine is cranking. This verifies that stator in distributor is operating properly and a sync pulse (signal) is being generated. If there is no sync pulse, replace stator.

EGR SOLENOID VACUUM TEST

1. Bring engine to normal operating temperature and curb idle. Check vacuum at solenoid vacuum source hose. Disconnect line and attach vacuum gauge. Vacuum should be minimum 15 in. Hg. If vacuum is low, check line for kinks, twists, or loose connections. If vacuum lines are okay, remove gauge and reconnect vacuum line.
2. Check vacuum at solenoid output port. Disconnect line and attach vacuum gauge to output port. Reading should be zero (no vacuum) this side of solenoid. If reading is zero, leave gauge connected and go to step 3). If vacuum is present, check solenoid and ECU operation with DRB-II and repair as necessary.
3. Disconnect electrical connector at solenoid and note vacuum at solenoid output port. Vacuum should now be present at output port. If vacuum is present, proceed to «EGR VALVE VACUUM TEST»(ref-24457-S23055897162001010500000) . If vacuum is not present, replace solenoid.

EGR VALVE VACUUM TEST

1. Disconnect solenoid electrical connector, if not already disconnected. By-pass vacuum transducer and connect EGR valve solenoid output hose directly to nipple on EGR valve and note engine idle. Engine should idle roughly or stall. If this occurs, valve is okay. Proceed to «EGR TRANSDUCER VACUUM TEST»(ref-24457-S42588260212001010500000) . If idle does not change, go to next step.
2. Disconnect hose from EGR valve and connect hand vacuum pump to EGR valve nipple. Apply minimum of 12 in. Hg vacuum to valve and note engine idle. If engine now idles roughly, inspect vacuum lines between vacuum connector on intake manifold and EGR valve, and backpressure hose from EGR base to transducer for leaks.
3. If no leaks are found, proceed to «EGR TRANSDUCER VACUUM TEST»(ref-24457-S42588260212001010500000) . If idle did not change, remove EGR valve and inspect exhaust passage in manifold for blockage, repair as necessary. If no blockage is present replace EGR valve.

EGR VALVE OPENING TEST

With engine at normal operating temperature and curb idle speed, quickly open and close throttle. Throttle should open sufficiently to allow engine speed to reach 1500 RPM. A distinct movement should be noticed in EGR control diaphragm. If diaphragm does not move, check for a faulty or leaking vacuum hoses, defective EGR valve diaphragm, or a defective backpressure sensor diaphragm.

EGR VALVE CLOSING TEST

1. With engine at normal operating temperature and curb idle speed, manually depress EGR valve diaphragm. There should be an immediate drop in engine RPM (indicating that EGR valve has been properly preventing flow of exhaust gas to the intake manifold at idle speed). If there is no change in RPM and engine is idling properly, exhaust gases are not reaching combustion chamber. Check for a restricted passage between EGR valve and intake manifold.
2. If engine idles improperly and RPM is not greatly affected by depressing EGR valve diaphragm, EGR valve is not preventing flow of exhaust gases to intake manifold. There is either a fault in the vacuum hoses, improper hose connection or valve is defective.

EGR TRANSDUCER VACUUM TEST

Disconnect transducer vacuum lines and backpressure line. Remove transducer. Plug transducer output port. Apply 1-2 pounds air pressure with a hand pump or regulated compressed air to the exhaust backpressure signal port of transducer. Apply minimum of 12 in. Hg to vacuum input port. Replace transducer if it will not hold vacuum.

SYSTEM TEST

1. Start engine and allow it to reach normal operating temperature. Ensure engine is at normal curb idle. Remove PCV valve from grommet. If valve is okay, hissing will be heard as air passes through it. Strong vacuum should be felt over inlet valve.
2. With finger over valve inlet, check for vacuum leaks at all connections. Reinstall PCV valve and remove crankcase air inlet hose at air cleaner.
3. Loosely hold piece of stiff paper over opening at end of inlet hose. After about a minute, paper should be sucked against hose opening with noticeable force. Remove and shake PCV valve. Ensure metallic clicking can be heard, indicating valve is free.
4. If system passes both engine running and stopped tests, it is functioning properly. If it fails either test, replace defective components and retest. If it does not pass on second try, clean system.

AIR VALVE VACUUM MOTOR TEST

1. With engine off, detach ambient air duct at air cleaner and observe position air valve. It should be fully open to incoming ambient air (heat in OFF position). Use extreme caution when engine is operating.
2. Start engine and observe position of air valve. It should be fully closed to incoming ambient air (heat-on position).
3. Depress throttle rapidly (1/2-3/4 position) and release. Air valve should briefly remain stationary and then move toward heat-off position and back to heat-on position. Loosely attach ambient air duct to air cleaner and warm engine to normal operating temperature.
4. Remove ambient air duct and observe air valve. It should be either fully open to ambient air or at a mixture position that provides the correct inlet air temperature to carburetor. Stop engine and connect ambient air duct to air cleaner.
5. If air valve does not function as described, inspect for mechanical binds in snorkel, disconnected vacuum hoses, or air leaks either at vacuum motor, thermal switch, reverse delay valve, intake manifold or vacuum hoses.
6. If valve manually operates freely and no hose disconnections or air leaks are detected, connect a hose from intake manifold vacuum source directly to vacuum motor and start engine. If air valve closes, either thermal switch, reverse delay or check valve is defective and must be replaced. If air valve does not close, replace vacuum motor.

See also:
• TITANIA OXYGEN SENSOR TESTING