Oil on an O2

[jeepfiend]

So my '97 just threw a P1193, which is of course and O2 problem, specifically a downstream O2 problem. I replaced the upstreams a few months ago, so I figure no big deal, the downstream sensors have gone bad. I change the right side first, everything looks fine. I pull out the left side, and the sensor has oil on it . I am guessing this is the reason that it is throwing a code. I did get one other code, a high voltage on the same downstream sensor. Am I correct to assume that the oil will kill an O2?? I don't want to put in the other new sensor if there is oil in the exhaust (at $100/sensor I really don't want to take chances). Here is the strange thing, no code on the upstream sensor?!! If there is enough oil getting through the cat to soak the downstream sensor, wouldn't the upstream be dead too?? Aside from a very annoying yellow CE light, the rig is running just fine. No missing, no hesitation, no noticeable power loss, no hit on the mileage. So now, the $64k question, where is the oil coming from?? I am now at 135k on the odo, and new heads were installed at 75k, could I already have a bad valve? It seems to me that this oil could really only be from a bad valve guide seal. I guess I get to pull the heads. The valve cover gaskets needed to be replaced anyway. And the kick in the crotch, I just sold my diesel Series III to get my wife off my back, and I had enough money to get the tube bender I have been wanting, and the Disco does this. I guess the Disco is pissed that it has to be alone in the garage again. The old crusty Series must have been good company!

 

[Andrew Homan]

How much oil you using? also it seems hard to believe that much oil could get through without causing cat problems or at least a shit load of smoke. Is the oil actually on the end probe of the o2 sensor? Just asking. Let me know what you find its interesting

 

[jeepfiend]

My thoughts exactly! How on earth could oil be on the downstream sensor and not cause all sorts of trouble! The oil was right on the probe, inside the pipe. No smoke, no other symptoms besides a P1193, and a P0138 code. I have heard that any moisture, oil or anything like that will kill O2's, but this has me baffled. I suppose that a certain amount of moisture is inevitable, from condensation. Maybe what I saw on the sensor was a littl fuel condensation mix?? The other odd thing, the right side sensor looked like I thought it should, it had a little buildup, and some gunk, but it was dry, what I expected being downstream from a cat, but the left side was washed clean. Running as well as it is, and with no other symptoms, I am baffled. I will have to check the sensors electrically and see what I get. I suppose there is a nominal impedance that should be seen across the sensors, I will have to do some searching and see if I can find those values. Would moisture cause a high voltage fault on a sensor? Plus the 1193 code is an open short in the heater circuit, also consistent with a dead probe. But why no problems with the upstream sensor, that is what has me confused? And why no other symptoms?? I would think that if there was that much oil in the cats I would be leaving a smoke screen every where I go, and the upstream sensor would also be dead!

 

[Andrew Homan]

It would be interesting to look inside the cat or at least the pipe leading up to the o2 sensor. I would think water would affect the sensor causing faulty readings but not sure. an o2 sensor works with mili volts so I would think water would F%$#K it up. Wow weird problem!!!!

 

[jeepfiend]

As far as oil consumption, less than a quart per thousand miles, still well within LR's acceptable range. I was going to do the transmission filter soon, so that might be a good opportunity to look into the cats and the y-pipe. I might just take the $110 gamble and put in the new sensor and see what happens. I just can't imagine there is that much oil going through the cat, at least without there being a significant amount of smoke from the tailpipe. And no other codes, it really seems odd. I think I will take the old sensor from the right side and put it in the left and see if the code returns. If it does not come back in a thousand miles or so, I will put the new one in. My only hesitation is that the threads on the old sensor are a little chewed up, and I don't want to strip the sensor bung.

 

[Andrew Homan]

Maybe you can get a thread file or tap to chase the the threads so they don't get worse.

 

[jeepfiend]

Anybody know what the threads are on the O2 sensors? I am more and more thinking I will just take the $100 gamble and install the new sensor. None of this makes much sense. Maybe the fluid was just water, and combined with the gunk in the exhaust it just seemed like oil. I just can't imagine that oil can get past the cats without there being a lot of smoke.