Premium Fuel Tune - Long term fuel trims

[Leigh_bullitt]

Hi All
Quick question if I have a premium fuel tune and I add fuel which may either be slightly contaminated or less octane. Will this affect my Long term Fuel trims into negative 12%?.
also it’s 36 degrees centigrade here at the moment and the IAT temps are through the roof.

I asked because sometimes after refueling I can see the LTFTs taking a dive and a month later after fueling somewhere else or so they are back around -4%

thanks

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[EFI]

Octane difference shouldn't matter for LTFTs, but ethanol content would.

Something else is causing them to go that far off. Hence their name, they take a long time to adjust so something big is happening for a long time for them to go from -4 to -12. Have you looked at your STFTs or lambda?

 

[Leigh_bullitt]

Yeh
At idle lambda is 1.00 and Stfts 1.00. Using the sctx4 and these should be perfect.

I have to admit I did a Kam reset and the LTFTs plummeted. I’m guessing they may need time to come back up with a few drive cycles.

maybe the ecu doesn’t trust the O2 signals until the rediness is totally completed ?

 

[EFI]

At idle lambda is 1.00 and Stfts 1.00. Using the sctx4 and these should be perfect.

Then your fueling is spot on.

I have to admit I did a Kam reset and the LTFTs plummeted. I’m guessing they may need time to come back up with a few drive cycles.

maybe the ecu doesn’t trust the O2 signals until the rediness is totally completed ?

So yes, a hard reset like that will most certainly adjust the learned values and start off new so you might see funky LTFTs. And those take a while to be learned, so if they eventually settle at -4 then once again your fueling is pretty good. It's not so much that it doesn't trust the signals at first, but the long term fuel trims take a while of "learning" before they settle on something. STFTs and lambda tell you exactly what is happening at that moment with your fueling so if those are near 1 at idle or driving then you're fine.

 

[Leigh_bullitt]

Thanks for your help.
Looks like I was trying to solve a problem that I never had.

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