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Positive fuel trim, evap, o2,cat monitors not ready

693 Views 2 Replies 2 Participants Last post by  Moe0798
Need an experience tech!!! 09 Civic Si k20z3

No matter what I do, short fuel trim is high at idle, goes down to 0% under load.

I’ve replaced spark plugs(denso, just for routine maintenance ), upstream sensor(denso, it was running rich), maf sensor(denso).

Car is stock, only think is a typhoon CAI, but it had the same readings before adding the intake.

I already sprayed carb cleaner on all the lines around the injectors, throttle body, intake, brake booster . No change in rpms, what lines did I miss?

I put royal purple on an empty tank, filled it up, used up all the fuel(this was because i wanted to make sure my injectors weren’t clogged). Still nothing.

Other issue I’m having is my evap and o2 sensor monitors aren’t ready, not sure if they’re all related(I’ve tried drive cycle procedures multiple times, nothing).

The vehicle doesn’t have any idling or power issues, I only found out about the fuel trim when my vehicle didn’t pass inspection. And then it through a P0171(only one code) after inspection, it never through that code before then. The only code it was throwing before was too rich, o2 sensor upstream, and I replaced that. So how is it that it went from too rich to too lean?

I know it could also be a fuel issue, but I always use 93 and every where I read says that fuel trim going down under load means vacuum leak 99% of the time

I just want this vehicle to pass inspection 😖
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It sounds like you have done all the common things. It is possible the O2 sensor was giving a bad reading and it was compensating by pulling fuel. Now with the new one reading correctly it is lean.

Have you tried cleaning the MAF yet? Any dirt or contaminants on it can give bad readings which could be the cause.
Yes cleaned it twice and this is a new one too. I’m seeing it could be a bad purge vavle maybe?
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