Hey guys 2000 camaro 3.8 cars running very rich like long term -25 short term negative -15. It fluctuation all the way down to the to 5 sometimes but short and long term always stay negative. No codes. Took to dealer they had for a day the mechanic said the car runs better then some the newer cars they have and can’t find anything wrong but if you unplug the PUrge valve fuel trims come back down to a normal range so ani replaced that and still running very rich unless you unplug that. Any ideas ???

 

Do you have any other symptoms besides the fuel trim? How do the plugs look? With a MAF sensor a vacuum leak can cause the trim to read high, also coolant/air temp sensors. Heck it can be the MAF itself. Even bad 02's can cause it or a weak fuel pump could be the issue.

If you are not getting terrible gas mileage or fouled plugs or failing a sniffer then you not really running rich. The trim thinks its putting to much gas in the engine. Example, with a weak fuel pump the PCM has to cycle the injector longer to get the O2's to read right. The PCM thinks it dumping too much gas but its really fine. If the system is out of what the factory thinks is ok it will set a rich code.

 

No the car runs great the mechanic at the dealership said no misses nothing. All sensors work great. This just started couple months ago I’ve done a lot work to the car myself. New throttle body maf sensor EGr all the gaskets. I don’t think it’s a fuel problem could be wrong. No starting issues hot or cold. No stumbling up hill or hesitation. Just my gas mileage is **** maybe 15 mpg well should be upper or 20. Has car almost two years and fuel trims where always around 0. And if it was vacuum leak the car would run lean not rich. Cuz I have taken a vaccume line off and the fuel trims immediately jump positive.

 

You keep saying its running rich but it is not running rich. The PCM thinks its adding more fuel then the engine should need. This is not a problem it is designed to do this, stop looking at the fuel trim. This could be resistance in a wire/connector or even a weak driver in the PCM. If it get bad enough the PCM can not compensate it will tell you. If its not setting a code and has no symptoms you are within factory specs, We would not even try to "fix" this if the car was under factory warranty.

If you get a symptom rough idle, bad fuel mileage or a check engine light then worry about it. You have an 18 year old wiring harness that was designed to last 10-12 years the last thing you need to do is poke around trying to fix a non-issue and cause a real issue.

 

check brakes to make sure they are not dragging. check 02 sensors to make sure they are not fouled. check evap canister to make sure its not full of gas an messing things up. while there check evap hoses. test fuel pressure. thats all i got.