A/F Ratio Help

Synchros shot? Weird noises while shifting? Not sure what needs to be replaced?
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eaglecatcher
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A/F Ratio Help

Post by eaglecatcher »

Ok, so I got a CEL the other day. Had it a few times but it's gone away by itself. Took it to a shop and they said they weren't sure what it was, and to drive it around for a while and bring it back if it comes on again and they'll start replacing things. He thought O2 Sensor. Same thing as what I've thought for a while.

My question. The code says engine is running lean, and that neither bank can switch it or something to that effect. However, smelling the fumes, it DEFINITELY smells rich. I mean, sitting still with it running, it smells like gasoline for sure. My theory: O2 sensors are malfunctioning (the pre cat ones) and they tell the engine it's running lean, so it dumps more fuel in, but since they're malfuntioning, they don't realize when it's running normal A/F, and so it's dumping in tons of fuel, but can't correct itself.

Is this plausible? I'll probably replace the O2 sensors myself, just gotta find time to do so.
I mean the fumes are almost nauseating they smell so much like gas.
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Re: A/F Ratio Help

Post by Rope-Pusher »

Many times, a vehicle will go into limp-in mode if there is something wrong. Extra fuel isn't the best for the catalyst, but the engine will run more reliably when rich than when lean. Less likely to stall, hesitate, knock, backfire, etc.
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theholycow
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Re: A/F Ratio Help

Post by theholycow »

Sounds like O2 sensor too, but unless they're cheap I wouldn't recommend haphazardly throwing parts at it...I'd say try to troubleshoot more first.
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Re: A/F Ratio Help

Post by permabanned »

CEL coming on and shutting off is o2 sensor 99% of the time. other codes light up and stay on.
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Re: A/F Ratio Help

Post by watkins »

A misfire can sometimes cause a flickering CEL, but only an idiot wouldnt notice the other symptoms as something severely messed up.

O2 sensor is definitely a very likely culprit, and theres no way to confuse that with a misfire
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kamesama980
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Re: A/F Ratio Help

Post by kamesama980 »

what car/kind of engine is this btw?

any exhaust leaks? a leak before the o2 sensor can cause it to read more o2 which is then read as lean so the engine richens up but that won't balance out the o2 level so it keeps going.

vacuum leaks depending on the air measurement method. extra unmetered air going in. after a point it won't be able to adapt.

hows it running overall? I was working on a friends 1jz the other day and with a coilpack wired wrong not getting spark to a cylinder, the wideband read quite lean in spite of rich smell and black (rich) smoke. again, unused o2 going through a cylinder and out the exhaust being read by the sensor. If you have a cylinder not firing or barely firing, it'll do it.
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