97 XJ, P0171

I've read some of the threads, enough to go check the exhaust manifold for cracks, check to see if the upstream O2 sensor fuse was good, if it was plugged in. All was nominal. This is the same 97 XJ, 163K, AW-4, 4.0, from last summer that I couldn't get to run, and replaced plugs, wires, IAC twice, CPS, TPS, TPS harness, IAT, coil, both O2 sensors, distributor, computer, checked continuity on leads, checked resistance on grounds, probably more.

Recently, just before COfest like last year, it started wanting to die when the brake was pressed. I replace the brake booster to no avail. It had an aftermarket cruise control. Since I removed that today, it is better, but now has the 171 code. No vacuum leaks that I can discern. Every vacuum lead I disconnect causes an increase in idle speed. Haven't done any spray testing. Nor have I tested the fuel pressure, or tried fuel system cleaner, though I did a can of the Chevron stuff last year.

I have a Turbogauge, a knockoff of the Scan guage. The FTZ reported is always for the NSS, which I already replaced, and in the opinion of a trans shop has nothing to do with it. I've been reading about STFT and LTFT, but I can't say it has completely sunk in yet.

I'm taking it to the recommended shop for electrical problem tomorrow, but I'd still like your input.

Thanks,

Fred

Do you what caused the lean condition? This is a good story, and I'm glad I went to the guy I did. Highland Auto, talk to Dave.

A little while ago, the kid backed the jeep into a tree, and took out the hatch and partially the drivers side taillight lense. Monsoon started and some corrosion started in the taillight. Apparently, whoever salvaged this jeep, neglected to attach the ground wires in the harness from the ECM and the TCM. The system was using the taillight ground to the body, and when it got dirty, the voltage drop was too much when the brake was pressed. Simple as that. If I ever meet that idiot, well, never mind. But it was the missing grounds that caused the problem. It helps to have schematics from Mitchell. Now I need to add the grounds to the harness.
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