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My '94 3.4l with 190k miles can not pass emissions test because it is running way too rich. The engine is putting out "gross polluter" amounts of carbon monoxide and hydrocarbons. You don’t need emissions testing equipment to tell the engine is running rich, you can just smell it
After the first failure I did a tune-up (spark plugs & wires), that made a 20% improvement. I then took it to my mechanic. He "looked" at it and suggested I replace the catalyst. I replaced it Sunday. But the emissions test Monday was no different. It still runs rich. I just checked the O2 sensors. They bounced between 0 and 0.8 V like they should. I believe my mechanic checked them as well, so I’d assume they're good? My mechanic said the EGR is working and fuel pressure checked out as well. I just pulled the vacuum line off the fuel pressure regulator, it has good vacuum.
My engine has another problem on cold starts where the idle bounces around between 2000 RPM and just above stalling that I would like to believe is related to the richness problem. My guess is there is something wrong with the PCM. The way it runs on start-up is similar to how it runs after disconnecting the battery. Start-up is really no different between disconnecting the battery and running for weeks. Am I correct in saying after losing power the engine has to “learn” how to run again? It’s like it never learns. Power seems to be normal. It doesn’t back-fire. Under heavy loads it will hesitate, but that was before the tune-up and new cat. The engine runs much stronger since the new cat and tune-up, that’s what’s had me frustrated and my mechanic baffled.
Maybe the computer just needs reflashing? Maybe it’s malfunctioning. My mechanic found no codes. I'm really getting desperate here. Please help!
After the first failure I did a tune-up (spark plugs & wires), that made a 20% improvement. I then took it to my mechanic. He "looked" at it and suggested I replace the catalyst. I replaced it Sunday. But the emissions test Monday was no different. It still runs rich. I just checked the O2 sensors. They bounced between 0 and 0.8 V like they should. I believe my mechanic checked them as well, so I’d assume they're good? My mechanic said the EGR is working and fuel pressure checked out as well. I just pulled the vacuum line off the fuel pressure regulator, it has good vacuum.
My engine has another problem on cold starts where the idle bounces around between 2000 RPM and just above stalling that I would like to believe is related to the richness problem. My guess is there is something wrong with the PCM. The way it runs on start-up is similar to how it runs after disconnecting the battery. Start-up is really no different between disconnecting the battery and running for weeks. Am I correct in saying after losing power the engine has to “learn” how to run again? It’s like it never learns. Power seems to be normal. It doesn’t back-fire. Under heavy loads it will hesitate, but that was before the tune-up and new cat. The engine runs much stronger since the new cat and tune-up, that’s what’s had me frustrated and my mechanic baffled.
Maybe the computer just needs reflashing? Maybe it’s malfunctioning. My mechanic found no codes. I'm really getting desperate here. Please help!
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