Rich condition even after O2 sensor change

[87SC/SS]

Hey All,

I've got a baffeling situation here. My 3.4L 94 Camaro runs rich only when it goes it closed loop. It runs great on start up, after about 5 minutes of running the idle drops as it should and then it runs ok for about a minute at low idle. After that minute it starts dumping fuel in to the point where it'll make your eyes water if you walk behind the car. Tons of smoke from the tailpipes. I changed the O2 sensor with a brand new set of AC Delco replacements - the numbers on the old sensors match the new ones (the old ones are original). It's still doing it and for the life of me I can't think of what else would be causing it other than a bad ECM.

The motor is rebuilt, it has an aftermarket cam, p&p heads, lower intake and plenum, headers, full exhaust, 19lb injectors. When upgraded the injectors to 19lb, the car ran fine for quite some time. When this problem started I swapped in the 17lb injectors and it still ran way rich, then I had the ECM flashed, same problem. I put the 19lb injectors in (which the ECM is now programmed for), and same problem. I cannot think of any other sensor that could be causing this. Any thoughts?

Thanks,
Brian

[87SC/SS]

Re: Rich condition even after O2 sensor change

Nothin'!?!?

[bigbrian442]

Re: Rich condition even after O2 sensor change

Check the MAP sensor.

[thebeewantsboost]

Re: Rich condition even after O2 sensor change

unplug the maf it should still go into open loop and run off map. i don't believe map readings are used unless the maf fails.

[87SC/SS]

Re: Rich condition even after O2 sensor change

Thanks for the replies guys,

@bigbrian - I changed the MAP and it didn't help.

@thebeewantsboost - It's a 3.4L so it's speed density and doesn't have a MAF.

I even tried another PCM and it made no difference. I had a buddy hook it up to his Tech 2, and it showed the injector pulses at 9ms at idle - which he said is what you would expect at WOT. Also it's not actually making it to closed loop - it's staying in open loop, but it doesn't start dumping the fuel in until it's been running for about 3-4 mins. I can't figure out for the life of me what's causing this.

[bigbrian442]

Re: Rich condition even after O2 sensor change

Have you looked at the ECT sensor reading though the tech 2?

[Skinny]

Re: Rich condition even after O2 sensor change

Look for intake/vacuum leaks as well as exhaust leaks. An exhaust leak anywhere upstream of the o2 sensors (like at the head) or within about 12 inches downstream of the o2 sensors WILL cause the o2 sensors to read lean, which will in turn cause the pcm to continue adding fuel, even if it's already running rich.

[bigbrian442]

Re: Rich condition even after O2 sensor change

An exhaust leak anywhere upstream of the o2 sensors (like at the head) or within about 12 inches downstream of the o2 sensors WILL cause the o2 sensors to read lean, which will in turn cause the pcm to continue adding fuel, even if it's already running rich.

Not running in open loop. O2's don't affect fueling until the PCM goes into closed loop.