Hi jag community, new here. Car specs: 1997 XJ6 (base model).

About a month ago my jag began to stall out on me when coming to a stop, however it would start back up and drive ok until the next stop light.

Scanning the car reveled an issue with the o2 sensor (p0138), so i quickly ordered a new one and had our mechanic install it. After that, the car ran exceptionally well for about 2 weeks, until it began stalling again.

Scanned it again, and now its showing that two o2 sensors are bad (p0138 again, plus p0158). I thought maybe, by chance, i had purchased a faulty sensor, so i ordered two more OEM sensors (both downstream) and had them installed.

Car ran great for a few days and started stalling out again. Same two codes came back (p0138, p0158) and now i am starting to think that maybe the o2 sensors are being fouled by something, perhaps oil.

The reason i think its oil related is because the first o2 sensor i replaced (the one that lasted two weeks) had black soot on the sensor after i got it back from the mechanic.

My question is: Do you think this recurring o2 sensor problem could be caused by some type of oil leak fouling the o2 sensors? And if so, which hoses/valves/etc might cause such a problem.

Sorry for the semi-long writeup. Thanks for reading. Any suggestions would be greatly appreciated.

 

It's possible, yes, but my experience is that it takes quite a fair amount of oil burning to do so. How much oil are you using?

Cheers
DD

 

I am with Doug. If it is oil contamination, it would be a bunch and you would see a cloud, I suspect.
It MIGHT be that the problem is there, then after the code sets, the car holds in open loop control. Before I replaced the O2s again, I would reset the codes and see if the car changed performance right away. Then i would have a look at the LTFT and STFT numbers and see what the pre and post cat lambdas were indicating in relationship to each other. And I would check the lambda heater circuit with a voltmeter (at teh sensor).

 

Thanks for the feedback, guys.

@Doug: The car doesn't seem to be using anymore oil than normal (1 quart/1000ish). Had the oil changed about 700 miles ago and haven't had to add anymore just yet.

@sparkenzap: No excess smoke or cloud coming from the exhaust. So maybe its not oil contamination after all.

I failed to mention this before, but i did clear the codes and the car actually ran fine for a short period of time (10-15 mins) before it began stalling again.

I'm not familiar with the LTFT, STFT numbers you mentioned, nor do i have a voltmeter handy. And after pondering the idea for awhile, i think my next step is to swallow my pride, forget about self-diagnosing the problem, and take it to another mechanic (the one my go-to mechanic actually recommended that i take it to.)

Rest assure, i will report back here after i get the problem fixed!

 

Well, you needn't swallow anyhting, if you do not have the equipment. The STFT and LTFT refer to the long and short term fuel trims. They are indications of what the oxygen sensors are reading and how the sensors are affecting (or "trimming") the engine. Many OBDII scanners will display or chart these paramaters.
One more thing based on your last info... Are yiou SURE the sensor connectors are not swapped?

 

IMHO that's not enough to cause a problem.

Sounds a bit high for an AJ16 engine (they usually don't use much oil.... mine uses 1qt every 3000-4000 miles, for example) but I don't think it would cause an O2 sensor problem.

Cheers
DD