cherokee513

I am getting this code (1391)on a 98 Jeep Cherokee 4L straight 6. The problem is a miss/hesitation/shudder when near 2000rpm under load. If you stomp on the gas and get above 3000rpm it will run like hell and not miss at all.

I have replaced the CKP (crankshaft sensor) and CMP (distributor pickup sensor ). I have also replaced the plugs, plug wires, coil, distributor cap and button.

I have also recently replaced the rear or downstream OS sensor do to a high voltage code. Both OS sensors seem to be operation in the 250-800mv range currently.

I have 3 main questions: Can anyone tell me or have documentation on how to check the wire harness to trouble shoot a possible intermittent signal? I have inspected the harness and noticed no obvious breaks or whatnot. The sensor harness connectors are getting 5v but I need more information on how to trouble shoot back to the computer.

Second: Would a worn distributor gear cause this problem. If I remove the cap the button will turn slightly in either direction.

The third question is about fuel trim. My test tool show long term and short term fuel trim on what is labeled as bank 1 and 3. (why not 2 and 4?).
the fuel trim on bank 1 is within 7% + or -. The bank 3 is always in the -38% range which I suspect is way out of range. What exactly is a bank? Does this represent a group of injectors? Is this directly controlled by the upstream OS2 sensor? Could this sensor be bad even when it is running a correct voltage fluctuation?

Any thoughts would be appreciated.

James

cherokee513

UPDATE 3-28-10

After a week of troubleshooting the wiring harness and finding only that the voltage returning to the computer from the NEW Crankshaft Sensor was not exactly what it should be I decided to pull it for a closer look. I carefully examined the old sensor compared to the new one to find that the new sensor was about a 1/32 of an inch shorter and the mounting holes in the bracket were drill just off center. I believe this small difference in distance from the flywheel was effecting the voltage output to the computer causing it to be just out of spec and throwing a 1391 code. In this case I should have just bought a more expensive "dealer" part and save myself some time. Always check the aftermarket parts carefully is the lesson I learned. Luckily the manager at Reilly's Autoparts was a stand up guy and refunded my money after showing him the difference and the problem it was causing.

Runs like a dream now.