Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
If a vehicle has large fuel trim corrections, (not maxed out, but large) and it runs poorly, would that be a sign that the fuel trim corrections were false, (not needed)? And if a vehicle had large fuel trim corrections but ran well, would that be a sign that the fuel trim corrections were correct, (actually needed)?
I have a 1.8L Pontiac Vibe that has large lean corrections when first started on really cold days. Once it warms up, fuel trims are great, around 5% total. On non-cold days, fuel trims are great. I noticed this 40° morning that while idling, the engine was kind of surging. That made me wonder if the engine was struggling because it really didn't need all the added fuel from the 35% positive fuel trim correction.
By the time I got to the next traffic light, the engine had fully warmed up and fuel trims corrected back down to normal.
Maybe I could have shortened my question down to just this, if the vehicle has a lambda of one, then it really did need whatever fuel trim corrections were happening. But if the lambda was not one, would that be a sign that it's a false lean or false rich if the fuel trim correction percentages are high, but not maxed out?
Big fuel trim corrections on a MAF engine at cold start could be cause by leaking seals that get tight with higher temperatures, especially rubber seal at the intake.
Though being maxed out the fuel trim corrections may still be to less to achieve lambda of 1. In this case you would have to look at the trim and lambda directions.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
The following user(s) said Thank You: timothy.spencer, Lupe
Topic Author
