Sup,
So I have been having a little trouble with my car lately, not really to do with my question but got me thinking. I'm new to tuning so yeah might be a dumb question haha.
So say you have your car tuned and all is good, then you start developing problems. In my case I'm getting bad mpg.
I was looking at my fuel trims on the interceptor gauge and in closed loop to trims are - double digits where in open in open loop they were pretty close to 0.
Would I be right in thinking because it's adding the correct air fuel in open loop, rather than a tuning problem it would more than likely be a mechanical problem (sensor etc)?

 

When is the last time your up stream O2 was replaced?
Is your coolant temp reading correctly?
Do you have a MIL for a bad MAP sensor?

Your tune will not just change itself so if everything was fine and now it is not, you have a mechanical or electrical issue that you need to trace down. I would start with the up stream O2.

 

yep^

also, trims go to 0 in open loop no matter how good or bad your afr is. so that is not an indication of anything

 

Aah that's a good point.