I bought a 140,000 mile 2001 TJ a few weeks back and have been picking away at the few issues it has. I had a '98 for about a decade so I was pretty familiar with the TJ and just wanted another with my daughter starting to drive. I used to be a regular on the Jeep Journal forums back in the day but it seems that's long gone.
Anyway, I started getting P0432 shortly after buying and starting to drive it. I'd clear it and it would sometimes stay gone for 50-75 miles but other times it would come back in a matter of just 8-10 miles. It appears to have new O2 sensors and I looked up some of the part numbers and they appear to be the legit NTK sensors. So, I was figuring I likely just needed to bite the bullet and replace the pre-cats... but, what I've found out is that if I keep the fuel tank topped off (above 2/3 tank) it'll never throw a code. It only throws the code if I let it drop below 2/3 tank. Once it's below 2/3 tank it'll throw the code and it'll come back pretty quickly if cleared (usually within about 8-10 miles of driving). I've now been driving for hundreds of miles over the course of over a week without the code being thrown by topping the tank off whenever it hits about 3/4. Previously I'd have gotten a check engine light several times over by now based on the rate I was getting it when I was using a more "normal" re-fueling interval. I'm going to continue this experiment for a few more days before letting the fuel level drop below 2/3... but, at this point it's pretty definitive that I will not get a P0432 unless it's below about 2/3 tank.
So, this seems like it's got to be an evaporative emissions leak issue that somehow doesn't introduce enough oxygen to alert the sensor until the fuel level drops. Maybe due to the amount of airspace in the tank? Pretty much all of the vacuum fittings look dry rotten and bad but I've tried pumping propane over all of the relevant gear and fittings and I never can detect a leak. I was able to rev the engine perceptibly by putting my un-lit torch against the air intake so I know I'm providing sufficient propane volume. I've not done a smoke test yet. The strange thing however is that I don't get any kind of definitive evap leak code. If the evap system is leaking bad enough for the downstream O2 sensor to detect it I'd expect to also see a code for at least a minor evap leak and I'm not getting that, just the P0432. Maybe the leaks are minor enough that when it checks the evap system at startup it is within limits but at higher vacuum levels it introduces enough O2 to throw the catalyst inefficiency error without ever showing an evap leak?
Any other ideas? Also, is there just a parts list to order to replace all of the vacuum fittings in the evap system? I'm not sure it's even worth trying to chase down leaks until I've got all fresh elbows and what not as they're pretty much all dry rotten and cracked. I probably should start with replacing all of the visibly bad pieces (some I can flex and then visibly see a leak) before trying to find leaks I can't see.
Anyway, I started getting P0432 shortly after buying and starting to drive it. I'd clear it and it would sometimes stay gone for 50-75 miles but other times it would come back in a matter of just 8-10 miles. It appears to have new O2 sensors and I looked up some of the part numbers and they appear to be the legit NTK sensors. So, I was figuring I likely just needed to bite the bullet and replace the pre-cats... but, what I've found out is that if I keep the fuel tank topped off (above 2/3 tank) it'll never throw a code. It only throws the code if I let it drop below 2/3 tank. Once it's below 2/3 tank it'll throw the code and it'll come back pretty quickly if cleared (usually within about 8-10 miles of driving). I've now been driving for hundreds of miles over the course of over a week without the code being thrown by topping the tank off whenever it hits about 3/4. Previously I'd have gotten a check engine light several times over by now based on the rate I was getting it when I was using a more "normal" re-fueling interval. I'm going to continue this experiment for a few more days before letting the fuel level drop below 2/3... but, at this point it's pretty definitive that I will not get a P0432 unless it's below about 2/3 tank.
So, this seems like it's got to be an evaporative emissions leak issue that somehow doesn't introduce enough oxygen to alert the sensor until the fuel level drops. Maybe due to the amount of airspace in the tank? Pretty much all of the vacuum fittings look dry rotten and bad but I've tried pumping propane over all of the relevant gear and fittings and I never can detect a leak. I was able to rev the engine perceptibly by putting my un-lit torch against the air intake so I know I'm providing sufficient propane volume. I've not done a smoke test yet. The strange thing however is that I don't get any kind of definitive evap leak code. If the evap system is leaking bad enough for the downstream O2 sensor to detect it I'd expect to also see a code for at least a minor evap leak and I'm not getting that, just the P0432. Maybe the leaks are minor enough that when it checks the evap system at startup it is within limits but at higher vacuum levels it introduces enough O2 to throw the catalyst inefficiency error without ever showing an evap leak?
Any other ideas? Also, is there just a parts list to order to replace all of the vacuum fittings in the evap system? I'm not sure it's even worth trying to chase down leaks until I've got all fresh elbows and what not as they're pretty much all dry rotten and cracked. I probably should start with replacing all of the visibly bad pieces (some I can flex and then visibly see a leak) before trying to find leaks I can't see.
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