mikjensen

I have a 98 XJ with 4.0. While under the Jeep last summer I noticed the wiring for the rear O2 sensor was resting on the drive shaft and that the insulation was stripped off one of the wires. I used zip ties to keep it up off the drive shaft and forgot about is until this spring. By then I had a constant check engine light. I bought a cheap code reader and it said the Rear O2 sensor was bad, so I replaced it. The light went away and I thought everything was good. A few weeks later the check engine light was back and this time it was for the heating element on the front O2 sensor. I replaced that one also. Now I will get the check engine light for a few days, always the front O2 sensor heating element and when the light is on, the Jeep runs well. When the light goes off, I get rough idles, but not constantly, usually after it warms up and I am waiting at a light. I also get an occasional backfire, usually when taking off from a stop. Yesterday, the Jeep would crank but not start on the first try, but if I stopped cranking and tried again, it started right up. I purchased 2 different O2 sensors, the rear is a Bosch and the front is a OEM. I have read some posts that say you have to go with OEM on these, but it seems strange that the Front sensor, the OEM, is the one throwing codes. Any ideas in this would be greatly appreciated.

CCKen

Check the O2S Heaters fuse in the PDC. Pic.



Inspect all the O2S wiring for chafing, breaks, etc., Look closely at the upstream O2S harness wire loom as it passes over the intake manifold for chafing.

Do not mix O2S brands - Bosch/NTK. Stay with NTK for all O2S'.