My fuel trim insanity continues.

[Dirtman]

Yea yea your sick of it... but new findings

Start the engine cold and the short term fuel trim is off (negative) and within 30 seconds brings the long term fuel trim to a place I'm happy with. +10%. And then short term is zero.

All good, drive around even under extreme load long term hits +6% so not a huge difference. Im super happy with 10% idle and 6% load.

Now here's what Ive found. After the engine runs for an hour or so and everything is heat soaked, when I stop and idle the idle long term fuel trim will jack up to 17%. (Short term zero).

Let the truck cool overnight same thing, starts high, corrects quickly down. Why does my idle fuel trim go so high after the engine is hot?

 

[scotts90ranger]

Probably correcting for air temperature, if the intake temperature is still reading high like you were talking about the engine will pull fuel correcting for that but then probably add it in with the closed loop system...

If the fuel mileage is reasonable I'd probably not worry about it, it has checks and balances, but then again I'm somewhat curious like you are, but I give up easy... my '00 Explorer reads idle load higher than expected but I think the engine is just worn out...

 

[adsm08]

Is it setting a code? If it isn't setting a code for rich or lean your perception of the fuel trims is just that, your perception. The software on the computer is the final arbiter of if anything in the fuel trims is actually a problem or not, so until it says there is a problem (sets a code) there is no problem, except with your perceptions.

 

[sgtsandman]

Is it setting a code? If it isn't setting a code for rich or lean your perception of the fuel trims is just that, your perception. The software on the computer is the final arbiter of if anything in the fuel trims is actually a problem or not, so until it says there is a problem (sets a code) there is no problem, except with your perceptions.