'98 XJ p0171 code

mbalbritton

mbalbritton

#@$%!
Joined
Mar 22, 2005
Location
Lakeland, FL
On the drive home today the check engine came on. Started watching and listening to everything. Engine running fine off idle. Little rough at idle. Then I saw the temp gauge drop from 210 to about 105. Then go back up and back down

Stopped at the store and scanned it. p0171 code. Fuel bank 1

Looked under the hood and there is a crack in the header at the split. Typical of the I-6.

While sitting there running at the store, noticed that the idle was up and down and you could smell it running rich. Parts store guy said O2 sensor. He also pointed out the header crack.

Question before ordering O2 sensor. Could it be just the cracked header giving a false reading at the O2 and the computer dumping extra fuel?

But that still doesn't explain to me the fluctuation from the temp gauge. Obviously my temp is actually changing by 100* in a matter of a two minutes.

Anyone have experience with this?
 
Any exhaust leak will cause O2 to read lean, and as you thought, make computer add fuel. Fix your manifold, don't throw a sensor at it.
I can't see an engine being capable of 210-105 in two minutes, I think it would crack the block. I do think you may have low coolant, or a problem with the sender,gauge or circuit.
 
Low coolant & no visible leaks, suspect the head. Will also make it lean out and enrichen to compensate.. leak down test will tell. Usually unless the crack is open enough to hear it, it won't cause it to lean enough to set the code because it requires ltft or stft to exceed 25% (maybe 20) for some duration of time. Rough at idle is also symptom of a cracked head. I've got at least 3 good heads here if that's the case. But like I said, a leak down test will prove a cracked head/blown gasket leaking into combustion chamber. Take time to diagnose it and save money by not throwing parts at it. If you have a scanner capable of graphing data, graph the upstream o2. It should fluctuate fairly rapidly(once per second at least). If it doesn't, it is more probably the sensor than the leak. Typically failed o2 sensors trip the oxygen sensor monitor and will throw a o2 sensor code (slow to switch, sensor performance, etc).. my 50 cents.. increased from 2 cents to compensate for inflation.
 
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