Originally Posted by stormtj
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.