Mechanics

GRAND CHEROKEE SPORADICALLY DIES WHILE DRIVING

1995 Jeep Laredo

Engine Mechanical problem
1995 Jeep Laredo 6 cyl Four Wheel Drive Automatic 224000 miles

Okay, this one is stumping my feeble mechanical abilities.

It all started with a bad idle. ZJ 4.0 would run fine for days and days then while sitting at a light, the idle would dip to 250 and go back up. Only to not do it again for a day or so.

Then, one day, I was at a Mall, got in the Jeep to start it and it wouldn't start. Turned over fine, but wouldn't fire. I put it in neutral, tried again and it started.

Then, it happened again, this time neutral didn't work. I played with the relays and it started.

Then it happened again, this time the relays made no difference. I just had to wait and try it periodically. Then it started.

Still thinking it was the relays, I replaced the fuel pump relay and the ASD relay. I also replaced the Throttle Positioning Sensor just for kicks.

But, it happened again. And again. And again.

Then I started noticing that while driving, it would jerk like it was going to die.

And then, tonight, driving home. It happened. On the freeway, a section with no shoulder, the RPMs went to zero, I kept on the gas pedal and the RPMs jumped to 2000 then fell back to zero, I pumped the gas and nothing, but I kept on it and it fired again but then back to zero, this happened a couple more times before completely dieing. I managed to coast long enough with the hazards on to make it to a safe shoulder.

I checked the relays. I checked the fuses. I used my iphone to search the forums. I checked the spark plugs to see if they were firing. Nothing seemed wrong.

And then she started again. I drove her home and the rig died three more times, each time I would have to wait and little bit, try it again and start it up.

I also replaced the plugs, wires and the cap & rotor.

So that's my story. Your insight is most appreciated!
Avatar
Pseudojeeper
January 29, 2010.



Is your check engine light on? If yes turn the key from off to on three times, on the fourth one leave it in the on position, count the flasshes...22 would flash as 2 blinks, then a short puase, then 2 more blinks...if several codes are stored, the pause is longer between codes, code 55 will be the last code...do this and post all codes found...
Could be a fauly connection to the crank or cam sensor, or PCM. Or a fulty crank, cam, or PCM...Crank sensor is on the bell housing left side and cam sensor is inside the distributor.


http://www.2carpros.com/forum/automotive_pictures/62217_4_17.jpg


Merlin2021
Jan 29, 2010.
No, the check engine light is not on.

Tiny
Pseudojeeper
Jan 29, 2010.
When it wont start you need to see what's missing, spark, gas, or compression(not Likley). Eliminate the working and tell us what's missing.
Start with the basics, and work your way up, Last tune up was? Wires plugs ALL filters? If all that is ok, check for a stuck EGR, then test fuel pump pressure, If it won't restart, determine what's missing, the engine needs three things to run, Spark at all plugs, gas to all cylinders, and compression in all cylinders, tho an engine may run lacking one in one cylinder, it won't run very well!
http://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm
Go here and checkout our video.
http://www.2carpros.com/car_repair_video/test_engine_ignition_system.htm
and this one!

Merlin2021
Jan 29, 2010.
Thank you for the feedback. Spark is fine, plugs having recently been replaced and checked when it died on the freeway.

Compression is good.

The mystery is why the fuel is shutting off.

Tiny
Pseudojeeper
Jan 29, 2010.
FUEL SYSTEM FUEL DELIVERY Fuel System Pressure Release Procedure 1. Disconnect negative battery cable. Slowly open fuel tank cap to release fuel tank pressure. Remove protective cap from pressure test port on fuel rail. 2. Using Fuel Pressure Gauge Tool Set (5069), obtain fuel pressure gauge and hose assembly. Remove gauge from hose. Place gauge end of hose in approved gasoline container. Place shop towel under test port. Screw other end of hose onto fuel pressure test port. Release fuel pressure. After pressure is released, remove hose from test port. Install protective cap on pressure test port. 3. If gauge tool set is not available, perform step 1). Using a small screwdriver, wrapped in shop towels, push test port valve in to relieve fuel pressure. Absorb spilled fuel with shop towels. Remove shop towels and dispose properly. Install protective cap on pressure test port. Fuel System Pressure Test 1. Remove cap from pressure fitting in fuel rail. See Fig. 1 . Using a shop towel to absorb any spilled fuel, connect a 0-60 psi (0-4.22 kg/cm 2 ) fuel pressure gauge to pressure fitting on fuel rail. Disconnect vacuum hose from fuel pressure regulator. Start engine. Fig. 1: Testing Fuel System Pressure Courtesy of CHRYSLER CORP. 2. Pressure should be approximately 39 psi (2.74 kg/cm 2 ) with vacuum hose disconnected and 31 psi (2.18 kg/cm 2 ) with vacuum hose connected to fuel pressure regulator. 3. If fuel pressure is not 8-10 psi (.56-.70 kg/cm 2 ) higher with vacuum hose disconnected from fuel pressure regulator, inspect vacuum hose for blockage, leaks, kinks or other damage. If vacuum hose is okay, replace fuel pressure regulator. 4. If fuel pressure exceeds 45 psi (3.1 kg/cm 2 ), check fuel return line for kinks or blockage. If fuel pressure is low, release fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE PROCEDURE heading above. Disconnect fuel return line on fuel rail near fuel pressure regulator. Connect 5/16" fuel hose between disconnected fuel return line and fuel rail. NOTE: Always relieve fuel pressure before disconnecting any fuel injection- related component. Also see appropriate fuel delivery system or fuel injector control circuit tests in G - 2.5L & 4.0L TESTS W/ CODES article in this section. CAUTION: Fuel pressure will rise as high as 100 psi (6.9 kg/cm 2 ) when fuel return line is pinched off. Ensure connections are properly secured. DO NOT pinch off hose for longer than 5 5. Restart vehicle and let engine idle. Momentarily pinch off hose connected to fuel return line. Note fuel gauge pressure reading. Pressure should rise to approximately 75 psi (5.2 kg/cm 2 ) within 2 seconds. 6. If fuel pressure rises as specified, pressure is operating at maximum capacity and is correct. If fuel pressure does not rise as specified, turn engine off. Release fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE PROCEDURE heading above. Raise and support vehicle. Disconnect fuel supply line at inlet (fuel tank side) of fuel filter. Connect 3/8" fuel hose between fuel filter and fuel supply line. 7. Restart vehicle and let engine idle. Momentarily pinch off hose connected to fuel supply line. Note fuel pressure gauge reading. Pressure should rise to approximately 75 psi (5.2 kg/cm 2 ) within 2 seconds. If fuel pressure rises as specified, but pressure is not same at fuel rail, check for plugged or restricted fuel filter. Also check fuel supply line between fuel filter and fuel rail for kinks or blockage. Fuel Pressure Leak-Down Test 1. Remove cap from pressure fitting on fuel rail. See Fig. 1 . Connect a 0-100 psi (0-6.9 kg/cm 2 ) fuel pressure gauge to pressure fitting on fuel rail. Start and run engine at idle. 2. Turn engine off and note fuel pressure gauge reading. Leave fuel pressure gauge connected. Allow 30 minutes to elapse and then compare fuel pressure gauge reading to reading taken when engine was turned off. 3. A pressure drop up to 20 psi (1.4 kg/cm 2 ) within 30 minutes is within specification. If pressure drop is not within specification, go to next step. If pressure drop is within specification, the fuel pump outlet check valve and fuel pressure regulator are operating correctly. 4. Release fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE PROCEDURE heading above. Disconnect both fuel lines at fuel rail near fuel pressure regulator. Connect 3/8" fuel hose between disconnected fuel supply line and fuel rail. Connect 5/16" fuel hose between disconnected fuel return line and fuel rail. 5. Start engine and record fuel pressure gauge reading. Turn engine off. Pinch off hose connected to fuel return line. Allow 30 minutes to elapse. If pressure drop is within specification, go to next step. A pressure drop of more than 20 psi (1.4 kg/cm 2 ) within 30 minutes indicates pressure is bleeding past fuel pump outlet check valve. Replace fuel pump assembly, located in fuel tank. 6. Pinch off hose connected to fuel supply line. Allow 30 minutes to elapse. A pressure drop of more than 20 psi (1.4 kg/cm 2 ) within 30 minutes indicates pressure is bleeding past fuel pressure regulator. Replace fuel pressure regulator. Fuel Pump Capacity Test 1. Release fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE PROCEDURE heading above. Disconnect fuel supply line at fuel rail near fuel pressure regulator. Connect 3/8" fuel hose to disconnected fuel supply line. Insert other end of hose into approved gasoline container. Start engine. Check fuel pump flow rate (capacity). 2. A good fuel pump will deliver at least 1.05 qts. (1.0L) of fuel per minute with return line hose seconds. pinched off. If fuel pump capacity is incorrect, inspect fuel supply system for a plugged filter or plugged fuel pump inlet filter. Fuel Pump Relay Some relays have battery voltage connected to terminal No. 30. Others have battery voltage connected to terminals No. 87 or 87A. See Fig. 3 . In de-energized position, relay should have continuity between terminals No. 87A and No. 30. Resistance value between terminals No. 85 and No. 86 should be 70-80 ohms for resistor type relays, or 81-91 ohms for diode type relays. FUEL CONTROL Fuel Injectors Disconnect injector from wiring harness. Connect ohmmeter on injector terminals. Resistance should be about 13.3-15.7 ohms at 68 °F (20 °C).
1/30/2010 ...


http://www.2carpros.com/forum/automotive_pictures/62217_FPG_1.jpg



http://www.2carpros.com/forum/automotive_pictures/62217_Relay_10.jpg



http://www.2carpros.com/forum/automotive_pictures/62217_PNS_1.jpg


Cam sensor and ignition switch need testing too, cam sensor controls injector timing. Ignition supplies power!

Merlin2021
Jan 30, 2010.
Try this for pulling codes, if anything other than 55 flashes, write it down and post here. Test these cicuits.
MODULES Theft Alarm Module (Cherokee & Grand Cherokee) 1. Turn ignition switch to ACC position 3 times and leave in ACC position to activate Security Alarm Module (SAM) self-diagnostics. If headlights do not flash, go to step 3). 2. If horn does not sound twice, go to step 9). If exterior lights do not flash, go to step 10). If parking lights and taillights do not flash, go to step 11). If horn sounds twice and headlights, parking lights and taillights flash, go to step 12). 3. Check for battery voltage at terminal No. 1 of security alarm module relay (located in relay center under glove box). If less than battery voltage is present, repair open to fuse No. 7 (15- amp) and retest. If system does not operate properly, go to next step. If battery voltage is present, go to step 5). If system operates properly, stop test procedure. 4. Using an ohmmeter, check continuity between security alarm module relay terminal No. 2 and headlight feed wires. If continuity exists, replace security alarm module relay and retest. If continuity does not exist, repair open in wiring circuit as necessary and retest. 5. Check for battery voltage at security alarm module relay terminal No. 3. If battery voltage is not present, repair open in wiring circuit as necessary. If battery voltage is present, go to step 7). If less than battery voltage is present, turn ignition switch to RUN position, then turn ignition off. 6. Check continuity between security alarm module relay pins No. 3 and 5. If continuity does not exist, replace security alarm module relay and retest. If continuity exist, check continuity between security alarm module terminal No. 7 (located behind center cluster bezel on instrument panel) and security alarm module relay pin No. 5. If continuity exists, replace security alarm module and retest. If continuity does not exist, repair open in wiring circuit as necessary and retest. 7. Turn ignition switch to RUN position, then turn ignition off. Check continuity between security alarm module relay pin No. 3 and ground. If continuity does not exist, repair open in wiring circuit as necessary and retest. If continuity exists, replace security alarm module relay with known good relay. If system does not operate properly, go to next step. If system operates properly, stop test procedure. 8. Using an ohmmeter, check continuity between security alarm module relay terminal No. 2 and headlights. If continuity exists, replace security alarm module relay and retest. If continuity does not exist, repair open in wiring circuit as necessary and retest. 9. Turn ignition switch to RUN position, then turn ignition off. If horn does not operate properly, NOTE: For identifying circuits referred to in testing, see appropriate wiring diagram in WIRING DIAGRAMS article in this section. NOTE: If SECURITY light comes and remains on with ignition on, the Chrysler Collision Detection (CCD) bus communication with the PCM has been lost. After servicing vehicle ensure that system operates properly. A malfunctioning anti-theft system may keep engine from starting. Check horn system for malfunction. Repair as necessary and retest. If horn operates properly, check continuity between security alarm module terminal No. 12 and horn relay connector. If continuity exists, replace security alarm module. If continuity does not exist, repair open in wiring circuit and retest. 10. Turn ignition switch to RUN position, then turn ignition off. If flash-to-pass does not operate, check and repair fuse No. 7 (15-amp) as necessary and retest. If flash-to-pass operates, check for battery voltage at security alarm module pin No. 21. If battery voltage is present, replace security alarm module. If voltage is less than battery voltage, repair open in wiring circuit to fuse and retest. 11. Check for battery voltage at lamp outage module pin No. 6. If battery voltage is present, repair open in light system. If voltage is less than battery voltage, check for battery voltage at security alarm module pin No. 14. If battery voltage is present, repair open in wiring circuit between security alarm module and rear lights. If less than battery voltage is present, replace security alarm module. 12. Ensure all doors and liftgate are closed. Verify that SECURITY light is flashing. If SECURITY light is not flashing, check bulb and wiring harness. Repair or replace as necessary. If bulb and wiring are okay, replace security alarm module and retest system. 13. If SECURITY light is flashing, turn ignition switch to OFF position. Remove illuminated entry relay from vehicle. Relay is located on a bracket behind instrument panel. 14. Check theft alarm switches by opening and closing doors and liftgate. Replace switch(es) or repair wiring harness as necessary. If switches are okay, check hood switch by opening and closing hood. 15. Replace hood switch or repair wiring harness as necessary. If hood switch is okay, unlock (with key) each front door and liftgate one at a time to test disarm switches. Replace switch(es) or repair wiring harness as necessary and retest system. 16. If disarm switches are okay, cycle power door locks to lock position and then unlock. If power door locks do not operate properly, replace door lock switch(es), lock/unlock relay(s) or repair wiring harness as necessary. Retest system. 17. If power door locks operate properly, lock and unlock vehicle with keyless entry transmitter. If power door locks do not operate properly, replace keyless entry transmitter, receiver or repair wiring harness as necessary and retest system. 18. If keyless entry system operates properly, turn ignition switch to ON position and wait 30 seconds. If SECURITY light comes on and stays on, repair or replace CCD bus and wiring as necessary and retest system. If SECURITY light remains off, theft alarm system is operating properly. NOTE: A functional PCM that has been used in a vehicle equipped with theft alarm system CANNOT be used in another vehicle that is NOT equipped with theft alarm system.
1/30/2010 . CRANKSHAFT POSITION SENSOR 1. Disconnect crankshaft position sensor. Connect ohmmeter across sensor terminal No. 2 (Black/Light Blue wire) and terminal No. 1 (Gray/Black wire on Cherokee and Wrangler; Red/Light Green wire on Grand Cherokee). 2. Ohmmeter should indicate an open circuit. Replace sensor if reading is not as specified. Also see appropriate crankshaft position sensor tests in G - 2.5L & 4.0L TESTS W/ CODES article in this section. MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR 1. Inspect MAP sensor vacuum hose connections at throttle body and sensor. Replace or repair vacuum hose if necessary. 2. Turn ignition on with engine off. Using DVOM, check MAP sensor output voltage. Connect DVOM to MAP sensor terminal " B" (Dark Green/Red wire on Cherokee and Wrangler; Red/White wire on Grand Cherokee) and ground. Terminal identification letters are marked on sensor body. 3. Output voltage should be 4-5 volts. Voltage should drop to 1.5-2.1 volts with a hot engine operating in Neutral and at idle speed. Also check for output voltage at PCM wiring harness terminal No. 1 on Cherokee and Wrangler or terminal No. 5 on Grand Cherokee. If voltage is not as previously specified, repair wiring harness as necessary. 4. With ignition on, check MAP sensor supply voltage at sensor connector terminal " C" (Violet/White wire). Supply voltage should be 4.5-5.5 volts. Also check for supply voltage at PCM wiring harness terminal No. 6. If supply voltage is not as specified, repair wiring harness if necessary. 5. Check continuity of MAP sensor ground circuit at sensor connector terminal " A" (Black/Light Blue wire) and PCM wiring harness terminal No. 4. Check continuity of MAP sensor ground circuit at sensor connector terminal No. 1 (Black/Light Blue wire) and PCM wiring harness terminal No. 4. Repair wiring harness if necessary. 6. Check continuity of MAP sensor ground circuit between PCM wiring harness terminals No. 4 and 11. If ohmmeter indicates an open circuit, go to next step. If ground connection is okay, replace PCM. 7. Check for defective sensor ground connection. Connection is located on right side of engine block, at oil dipstick tube mounting block. Repair connection as necessary. NOTE: If terminal No. 4 has a short circuit to 12 volts, correct this condition before replacing PCM. If necessary, perform appropriate MAP sensor tests in G - 2.5L & 4.0L TESTS W/ CODES article in this section. CAMSHAFT POSITION SENSOR 1. Use an analog voltmeter. DO NOT remove distributor connector from distributor. Insert voltmeter leads into backside of distributor wiring harness connector to make contact with terminals. Ensure connector is not damaged when inserting test probes. 2. Insert positive voltmeter lead into camshaft position sensor signal output circuit (Tan/Yellow wire on Cherokee and Wrangler; Gray/Black wire on Grand Cherokee) at distributor wiring harness connector. Insert negative voltmeter lead into ground circuit (Black/Light Blue wire) at distributor wiring harness connector. Set voltmeter to 15-volt DC scale. 3. With distributor cap removed, manually rotate engine until pulse ring enters sync signal generator on camshaft position sensor. Distributor rotor should be at 9 o'clock position. Turn ignition switch to ON position. With pulse ring positioned in the sync signal generator, reading should be approximately 5 volts. 4. If no voltage is present, check voltmeter leads for good connections. If connections are okay and there is still no voltage, check for voltage at supply circuit (Orange wire on Cherokee and Wrangler; White/Black wire on Grand Cherokee). 5. If no voltage is present at supply wire, remove PCM connector. Check voltage at PCM pin No. 7 and ground with wiring harness connected. PCM is located on left side of engine compartment. If there is no voltage at PCM, see appropriate camshaft position sensor circuit tests in G - 2.5L & 4.0L TESTS W/ CODES article in this section. 6. If voltage is present at supply wire, replace camshaft position sensor. If voltage is present at PCM pin No. 7, but not at supply wire, check continuity of supply wire between the distributor connector and the PCM. If no continuity exists, repair wiring harness as necessary. 7. If supply wire is okay, check continuity between camshaft position sensor signal output wire at the distributor connector and PCM pin No. 44. If no continuity exists, repair wiring harness as necessary. 8. If camshaft position sensor signal output wire is okay, check continuity between ground circuit wire at the distributor connector and ground. If no continuity exists, repair wiring harness as necessary. If ground wire is okay, go to next step. 9. While observing voltmeter, crank engine. Voltmeter needle should fluctuate from 0-5 volts while the engine is cranking. This verifies that camshaft position sensor in distributor is operating properly and that a sync pulse signal is being generated. If voltmeter does not fluctuate, replace camshaft position sensor.
1/30/2010 .

Merlin2021
Jan 30, 2010.
The codes are: 12 & 11

Tiny
Pseudojeeper
Feb 1, 2010.
11= No reference signal from Crank sensor
12= Battery power lost/disconnected within last 50 starts. Start with the crank sensor, mounted on the tranny bellhousing. Check Battery/ and cables, possibly the ignition switch.

Merlin2021
Feb 1, 2010.
Your jeep might have an alarm function that prevents the engine from starting. If that is the case you need to disable alarm.

Tiny
Ernesto123
Jul 4, 2011.
Instead of disable the alarm I meant to say disarm the alarm. Sorry for the mistake

Tiny
Ernesto123
Jul 4, 2011.
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