post #1 of Old 10-08-2010, 09:35 AM Thread Starter
stormtj
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Cleveland Ohio Mechanics

Any mechanics or people with jeep ignition/electrical experience interested in offering a helping hand. My 98 TJ is getting no spark and I am having major problems tracking down the problem. Willing to pay to help also just need my jeep back on the road asap...

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post #2 of Old 10-08-2010, 09:55 AM
rivalarrival
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Originally Posted by stormtj View Post
Any mechanics or people with jeep ignition/electrical experience interested in offering a helping hand. My 98 TJ is getting no spark and I am having major problems tracking down the problem. Willing to pay to help also just need my jeep back on the road asap...
I had a problem with these symptoms myself. When you turn on the key, does the check engine light illuminate for a moment? It should - this is part of the computer's self-test when it's switched on. If the CEL doesn't illuminate, the computer isn't coming on. Usual cause for that is a short circuit in an engine sensor, and the most likely culprits are the crankshaft position sensor and the camshaft position sensor.

Unplug them at their connections, one at a time, then both and check for the CEL to come on when you turn on the ignition. (Don't try to start - without the CKP and CMP, the engine will turn over but never fire) When the CEL comes on, whatever is disconnected is shorted.

I'm not sure where exactly the connections are on the 4.0. On the 2.5, the CKP connector is in the middle of the firewall, near the exhaust manifold. The CMP sensor itself is on the side of the bellhousing, near the top, up by the flywheel - trace the lead from it back to the proper connector. The CMP connector is on the wire leading to the underside of the distributor, with the sensor itself inside and integral to the distributor.

Of course, if you're having a different problem, none of this will help you... But this is a common enough problem that you should rule it out first, save yourself a few bucks.

I had BOTH the CKP and the CMP fail simultaneously. Make sure you check with both disconnected.

Good luck!

He that would make his own liberty secure, must guard even his enemy from oppression; for if he violates this duty, he establishes a precedent that will reach to himself. --Thomas Paine

We work together every damn day. --Jon Stewart

Any gas can be a knockout gas, when you wrap a steel cylinder around it and beat someone with it.

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post #3 of Old 10-08-2010, 02:10 PM Thread Starter
stormtj
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so far i have replaced the ckp and cmp coil, all relays, all fuses, and rotor, distributor is spinning when cranking, cap is in good condition. my instrument cluster randomly stopped working yesterday same symptoms as before it stopped working only now i really dont know if my cel is on. before i hooked a reader up and it said unable to communicate with computer.
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post #4 of Old 10-08-2010, 02:33 PM
rivalarrival
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so far i have replaced the ckp and cmp coil, all relays, all fuses, and rotor, distributor is spinning when cranking, cap is in good condition. my instrument cluster randomly stopped working yesterday same symptoms as before it stopped working only now i really dont know if my cel is on. before i hooked a reader up and it said unable to communicate with computer.
"New part" doesn't mean "good part". If the reader can't communicate with the computer, the computer is NOT coming on. It's possible (but unlikely) that the computer itself is bad, but it's more likely that a shorted sensor or melted and shorted wire is causing the problems.

Do what I suggested in my last post, even though you replaced the parts. If you've got a code reader, plug it in each time too. If it says it can't communicate with the computer, the computer is offline.

Disconnect each and every sensor on the motor if you have to. CKP, CMP, TPS, IAC, Oxygen, Temperature, Oil pressure... The computer contains a 5-volt regulated power supply inside the computer that powers a number of sensors. When that 5-volt bus is shorted out, the computer doesn't turn on.

When it happened to me, I put together this spreadsheet with the computer pinout. It may be useful to help you diagnose a problem. I developed it from the schematics in the YJ/TJ Haynes manual.

https://spreadsheets.google.com/ccc?...3aUVQcWc&hl=en



PM me with your location. Cleveland-proper is a bit of a haul for me, but if you're in one of the more southern suburbs, I might be able to stop by sometime this weekend.

He that would make his own liberty secure, must guard even his enemy from oppression; for if he violates this duty, he establishes a precedent that will reach to himself. --Thomas Paine

We work together every damn day. --Jon Stewart

Any gas can be a knockout gas, when you wrap a steel cylinder around it and beat someone with it.

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post #5 of Old 10-08-2010, 02:38 PM Thread Starter
stormtj
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this is using the pinouts in the connectors attaching to the computer correct? using that spread sheet?
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post #6 of Old 10-08-2010, 03:18 PM
rivalarrival
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this is using the pinouts in the connectors attaching to the computer correct? using that spread sheet?
Yeah, the spreadsheet shows the pinout for the three large connectors on the computer itself. I used it to supplement a Haynes manual, which never includes a raw pinout like that. If it's useful to you, great; if it's not, ignore it.

He that would make his own liberty secure, must guard even his enemy from oppression; for if he violates this duty, he establishes a precedent that will reach to himself. --Thomas Paine

We work together every damn day. --Jon Stewart

Any gas can be a knockout gas, when you wrap a steel cylinder around it and beat someone with it.

Low Output 4 Cylinder Jeep Club member #188
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