Short Term and Long Term Fuel Trims
 

This is pretty much aimed at the tuner-gurus but I'm always pleased to hear any feedback.

Recently my car has been experiencing some power loss. Seems fairly intermittent and is likely caused by a bad batch of gas from Sam's Club. Time will tell in a week or so when I can run all that crap out of my car.

Still, while troubleshooting this issue I noticed that the short term and even long term fuel trims were all over the place. For example, I could be sitting stationary and slowly bring the engine rpms up to about 2000 where the engine would run the roughest. My fuel trims would vary between -20 and +15 and would change very rapidly. This struck me as pretty odd.

So what I'm asking is have you all noticed this same behavior with your (or customer's) cars? I'm looking to get a tune next week (FA20's) and do you all think I should get this sorted out before I get the tune? My instincts say yes but I thought I would get some other opinions.

Scott

Hey Scott,

Last time I had a look a 100% stock car's fuel trims are normally with-in 10%.

Having a large fuel trim especially one that swings positive and negative will cause drive ability issues and loss of power.

Is your car 100% stock?

-John

Thanks for responding John!

I have an Injen intake but the car had been running perfectly with it for a month prior to this. I put the stock intake back on it and reset the ECU but no change.

Scott

I would check for small leaks