Lean idle in closed loop
Thread Starter
Staging Lane
Joined: Feb 2014
Posts: 68
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Lean idle in closed loop My 96 LT1 M6 has starts and drives well in any weather but has always run extremely rich in open loop anywhere from 12.1 in warm weather down to 10.4 in colder weather. In the past once it went into closed loop the AEM wideband would show 14.3-14.9.
Two summers ago the car was all of a sudden running rich all the time. I replaced the drivers side header gasket and the rich condition went away but ever since it runs lean in closed loop at 15.3-15.9 but the scanner shows the narrow bands at 14.7.
I wondered if perhaps the AEM O2 was no longer reading correctly after being subjected to a prolonged rich exhaust stream but the smell of exhaust indicates a problem beyond simply instrumentation.
The fuel trims are even for both banks pulling fuel from the base tables at 124ish or -1%. Seems reasonable. It also seems that would rule out other exhaust leaks or unmetered air? I haven't been able to find any.
Once possible piece of the puzzle is that after my passenger side cat self destructed for the third time I gutted the drivers side cat as well and installed a single metal core cat further down in the system. It's so far back that it does take longer to heat enough to do it's job but the smell of the exhaust is different when compared with or without it in place. So, it is doing something.
The impact here is that the downstream O2s are now ahead of the cat. But so what? Conventional wisdom says that the downstream O2s do not aftect fueling. The worst case should be an engine code for a malfunctioning cat right? Hmm, actually I don't have any codes at all..shouldn't I though?
Add in that the B2 downstream O2 has always been lazy. I've changed it twice over the years but it doesn't switch like the others. So, I'm wondering now if the downstream O2s do offer some correction in fueling after all. Assuming that the wiring to the lazy O2 isn't damaged (it's not a damaged PCM input. I've swapped it out and everything is exactly the same.) I wonder if O2 simulators might make any sort of a difference.
I'm expecting that I'll get a response along the lines of "you're totally over thinking this and haven't ruled out the basics. You need to go back and make sure that X..". Not sure what X is though..
Any Ideas?
Thanks,
Jon
Two summers ago the car was all of a sudden running rich all the time. I replaced the drivers side header gasket and the rich condition went away but ever since it runs lean in closed loop at 15.3-15.9 but the scanner shows the narrow bands at 14.7.
I wondered if perhaps the AEM O2 was no longer reading correctly after being subjected to a prolonged rich exhaust stream but the smell of exhaust indicates a problem beyond simply instrumentation.
The fuel trims are even for both banks pulling fuel from the base tables at 124ish or -1%. Seems reasonable. It also seems that would rule out other exhaust leaks or unmetered air? I haven't been able to find any.
Once possible piece of the puzzle is that after my passenger side cat self destructed for the third time I gutted the drivers side cat as well and installed a single metal core cat further down in the system. It's so far back that it does take longer to heat enough to do it's job but the smell of the exhaust is different when compared with or without it in place. So, it is doing something.
The impact here is that the downstream O2s are now ahead of the cat. But so what? Conventional wisdom says that the downstream O2s do not aftect fueling. The worst case should be an engine code for a malfunctioning cat right? Hmm, actually I don't have any codes at all..shouldn't I though?
Add in that the B2 downstream O2 has always been lazy. I've changed it twice over the years but it doesn't switch like the others. So, I'm wondering now if the downstream O2s do offer some correction in fueling after all. Assuming that the wiring to the lazy O2 isn't damaged (it's not a damaged PCM input. I've swapped it out and everything is exactly the same.) I wonder if O2 simulators might make any sort of a difference.
I'm expecting that I'll get a response along the lines of "you're totally over thinking this and haven't ruled out the basics. You need to go back and make sure that X..". Not sure what X is though..
Any Ideas?
Thanks,
Jon
