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Unread 09-11-2013, 02:59 PM   #1
tapalmer99
Registered User
1995 XJ Cherokee 
 
Join Date: Jul 2008
Location: Stamford, CT
Posts: 9
95 5.2 GC won't start

I have a 1995 Grand Cherokee with 160k.

I got home and turned off engine, 30 minutes later it wouldn't start. It just turns over but won't fire.

I get a spark when I put a wire near ground. I shot starting fluid down the throttle body, but didn't catch even once (I ruled out fuel pump due to that).

I was looking to replace the timing chain, as I thought it had jumped a tooth, but a mechanic said that was unlikely.

I am thinking Crank Position Sensor, or Cam Position Sensor - but didn't get any engine light warnings. Since I disconnected the battery to do work, I was told that any codes would have been lost.

Any help is appreciated. This is my primary vehicle.

Thank you!

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Unread 09-11-2013, 04:31 PM   #2
flash2225
Registered User
1993 ZJ 
 
Join Date: Jul 2013
Location: tumwater, wa
Posts: 44
Check out Zeejay1997's dirty dozen. Great read on how to diagnose a lot of problems.

http://www.jeepforum.com/forum/f13/1...talls-1407423/

If you suspect the Crank positions sensor this is a write that was put on my problem post by DELLIS.

Critical voltage tests
(1) While cranking your engine, do you have 12V present on the electrical connector of any fuel injector? Disconnect the electrical connector, and put a meter between the dark green/orange and a ground point (the engine block).
(2) While cranking your engine, test for spark through any of your spark plug wires.

Test 1 passes, Test 2 fails. You likely have a bad coil. Test the coil and replace if bad.
Test 1 fails, Test 2 fails. In this case, critical voltage is not being supplied to start your engine. Either the PCM is not activating critical circuits to start the car, or the ASD relay is defective. Go to test (3).
Test 1 passes, Test 2 passes. In this case, you need to go back and check fuel pressure because you most likely have a fuel problem.


ASD Relay Test
(3) Switch your ASD relay with a known good relay, say the horn relay. Attempt to start again.

Jeep starts. Your ASD relay was bad (or terminals corroded) and you have finished diagnosis.
Jeep does not start. The PCM is not activating critical circuits to start. Go to test (4)


CKPS Tests
(4) With the electrical connector disconnected and key in the "on" position, verify voltage to the CKPS from the PCM. It should be 8.0 volts for 1995 and earlier vehicles. Test between the white/black (voltage) and the black/light blue (ground) wires. If it is not 8.0 volts, then there may be a short on the 8volt line, or the PCM is having problems.

8.0 volts not present. You either have a short on your 8.0 Volt line, or your PCM is not generating 8.0 Volts. Go to test (7)
8.0 volts present. Your voltage supply to the CKPS is good, and you do not have a short. Go to test (5).


(5) Next check for damage to the CKPS ... place an ohmmeter across terminals B and C of the CKPS connector. The meter reading should be very high or open (infinite resistance).

Test fails. If you notice low measurable resistance, then the sensor is bad. Replace the CKPS.
Test passes. If the resistance was very high, typically above 10,000 ohms, then the CKPS may still be bad so we will need to do another test. Go to test (6)




(6) Reconnect the sensor and put a scope or meter on the signal line. Remove the plugs and attach a breaker bar and socket to the crankshaft pulley center bolt. Turn the key to the "on" position and slowly rotate the engine a full rotation while watching the meter. On a 5.2, it should dip from 8.0 volts down to ground every 45 degrees as it hits the notch on the flywheel.

Test passes. If tests (4), (5), and (6) have all passed, then your CKPS is good. At this point, additional testing would need to be done with the PCM, its connectors and wires to be certain ... but, probably, you have a bad PCM.
Test fails. If it is giving you other readings, then you have a bad CKPS. Replace it.




8 Volt Supply Testing
(7) If you are at this test, then you are not seeing 8 Volts being supplied to your CKPS. Disconnect the electrical connectors to your MAP, TPS, and Camshaft Position Sensor (CMPS, connector to your distributor). Repeat the procedure in test (4) above.

Test fails. If 8.0 volts is not being supplied to the CKPS after disconnecting these other components, then your PCM, its connectors or critical wiring is bad. Most likely, your PCM is damaged.
Test passes. If 8.0 volts is now present to the CKPS, begin connecting the MAP, TPS and CMPS one at a time ... if, after connecting one of these components you notice that the 8.0 volts disappears, then that sensor is causing a short and needs to be replaced.

Jeep starts. Your ASD relay was bad (or terminals corroded) and you have finished diagnosis.
Jeep does not start. The PCM is not activating critical circuits to start. Go to test (4)


CKPS Tests
(4) With the electrical connector disconnected and key in the "on" position, verify voltage to the CKPS from the PCM. It should be 8.0 volts for 1995 and earlier vehicles. Test between the white/black (voltage) and the black/light blue (ground) wires. If it is not 8.0 volts, then there may be a short on the 8volt line, or the PCM is having problems.

8.0 volts not present. You either have a short on your 8.0 Volt line, or your PCM is not generating 8.0 Volts. Go to test (7)
8.0 volts present. Your voltage supply to the CKPS is good, and you do not have a short. Go to test (5).


(5) Next check for damage to the CKPS ... place an ohmmeter across terminals B and C of the CKPS connector. The meter reading should be very high or open (infinite resistance).

Test fails. If you notice low measurable resistance, then the sensor is bad. Replace the CKPS.
Test passes. If the resistance was very high, typically above 10,000 ohms, then the CKPS may still be bad so we will need to do another test. Go to test (6)




(6) Reconnect the sensor and put a scope or meter on the signal line. Remove the plugs and attach a breaker bar and socket to the crankshaft pulley center bolt. Turn the key to the "on" position and slowly rotate the engine a full rotation while watching the meter. On a 5.2, it should dip from 8.0 volts down to ground every 45 degrees as it hits the notch on the flywheel.

Test passes. If tests (4), (5), and (6) have all passed, then your CKPS is good. At this point, additional testing would need to be done with the PCM, its connectors and wires to be certain ... but, probably, you have a bad PCM.
Test fails. If it is giving you other readings, then you have a bad CKPS. Replace it.
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Unread 09-12-2013, 01:42 PM   #3
tapalmer99
Registered User
1995 XJ Cherokee 
 
Join Date: Jul 2008
Location: Stamford, CT
Posts: 9
WOW!
Great ideas.
I also went to the original post.
This is all better than standing around with my thumb up my ***.
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