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Mechanic has thrown in the towel. HELP!

Hello all,
I know brevity is the soul of wit, so I’ll try and keep it short, although I could write a 2 pg paper on my car.
I have a 96 Jeep Cherokee Country, straight 6, 4.0 L engine, about 160,000 miles, with a remanufactured engine installed at 138,978 mi. The problem I am having is that when my car is in idle, it runs horribly. It kind of jumps and rumbles and you can smell gas. Also, I can hear a clacking sound, but only with the windows rolled up. My mechanic has tried to figure out what is wrong on two separate occasions, each for a week at a time and has thrown in the towel. He has even worked on it with a mechanic from another shop and that mechanic said he gives up also. He said the engine is running fine and the timing is fine, but the computer is saying my car is running lean and sending more gas, hence the rumbling while in idle. He reprogrammed the computer and it is still doing this. My Jeep has also gone from getting about 220 mi on one tank of gas to about 100 mi. Since it has been in his care I will give the list of things he has worked on.
5/30/13–Crank shaft sensor. 7/2/13–Ignition pick up coil. 7/9/13–Crank shaft pulley and serpentine belt. 8/17/13–Catalytic converter.
Any advice would be greatly appreciated!!!

Why did he put a new catalytic converter in it before fixing the root problem? A new catalytic converter can be ruined if too much raw gas gets into it, which may happen if the engine is running so rich.

First thing I’d do is find another mechanic. This one evidently is stumped.

My catalytic converter was going out. Rattling a lot.

If a remanufactured engine was installed this means that the intake/exhaust manifolds were removed and reinstalled. The intake/exhaust manifolds share a common gasket and are installed on the engine at the same time.

If leak developes in this common gasket, the air coming into the intake manifold can be scavanged by the exhaust gasses. This extra air in the exhaust gasses then comes in contact with O2 sensor which causes the O2 sensor to read a constant lean mixture. So the computer tries to compensate for this by dumping more fuel into the engine.


A lazy O2 sensor would also cause a rich condition. So would a bad fuel pressure regulator. The fuel pressure is not monitored by the PCM, so this has to be checked with a gauge, not a scan tool.

Looking at that list, it sounds like this mechanic is throwing parts at the problem at your expense.