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What year/model?
Posted by Bill S. [Email] (more from Bill S.) on Thu, 7 Oct 2004 18:52:13
In Reply to: What are the typical woes for failing a smog test......, 3pinFever, Thu, 7 Oct 2004 17:53:37
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Or, more to the point, which fuel injection does it have: CIS (79-84 + 85 N/A) or EFI (85 Turbo + 86-on N/A)?
There are lots of things that could cause a lean mixture (which is what it sounds like it has). Both systems are closed-loop feedback type - the O2 sensor monitors the exhaust, and the fuel injection is supposed to try to compensate accordingly. Seems to me your problem lies in one of two areas: either your fuel injection thinks it's mixing the fuel right (feedback regulation problem) or the initial mixture is so far off that the the feedback system can't compensate (e.g. large vacuum leak).
I saw lean mixture symptoms on an '86 900S (EFI) once. I checked the signal out of the O2 sensor, and it indicated a rich mixture (causing the ECU to lean the mixture). Turned out the O2 sensor was contaminated cuz Power Steering fluid had leaked all over it. Replaced the O2 sensor (and fixed the PS Leak) and all was well.
Not to suggest this is necessarily your problem, but you might try measuring the signal voltage coming out of the O2 sensor, to see what it says is going on. Under normal circumstances (correct mixture, all ok) the voltage should fluctuate around .5V for EFI cars. Lower voltage (nearer 0V) indicates a lean mixture (as reported by the O2 sensor), higher voltage (up to 1V) indicates rich.
posted by 24.18.226...
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