Thread: Very lean but only sometimes...

Hello, everybody! I just started piecing together some light mods on my 1997 GTP, but every once in a while, the SES light will come on. The code is for a system lean condition, but it clears its self after a few days. I checked the fuel trims at WOT and they are right around 0, but when I'm cruising they go to 16. Is this supposed to happen, or should I get a smoke test done?

Have you cleaned the MAF lately?

Negative trims like -16 means it's overally rich, a smoke test won't show you something there. a Postive fuel trim of +16 would mean it's trying to add fuel because it's lean.

I'd suspect a dirty MAF sensor or leaking fuel injector if the trims are always negative on a factory calibration.

Originally Posted by SgtMarshal

usually there is a vacuum leak when the fuel trims to positive. a misfire will make the fuel trims go lean as well.

I'd second that. Sounds like vacuum leak unless you are running e85 without a tune.

Check vacuum lines.

With it being a 97, I'm sure literally everything is dry rotted.

Replace all of those and do the intake gaskets as well. Could be those, too.