Idle fuel trim always goes to -12.5%
#1
Idle fuel trim always goes to -12.5%
I'm running into a strange issue during my tuning of 3dman1's built Evo 10. We've had three different sets of injectors in that car. I meticulously dial in the fuel trims, he takes the car home for the night, and when I check the trims the next day, the idle trim is at or near -12.5%. Anyone who has dialed in injectors knows that its very obvious when the idle trim is off by that much, and yet when I was tuning the injector settings, I had the STFT perfect at idle, and the idle trim would typically hold near 0% for 30 minutes of stop-and-go driving. All tuning was done with Access Tuner Race.
I have no idea of the cause, but I keep getting a gut feeling that its something some sort of error in engine control algorithm that reports the fuel trims. Curious if anyone else has seen this.
I have no idea of the cause, but I keep getting a gut feeling that its something some sort of error in engine control algorithm that reports the fuel trims. Curious if anyone else has seen this.
#7
Now on FIC1100s. Cruise trim is stable as a rock. Only other issue is the infamous radiator fan-induced unstable idle (to solved as soon as 3dman1 makes a shield that looks as good as the rest of his new English Racing 2.0L motor).
Last edited by mrfred; Jul 22, 2011 at 12:29 PM.
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#10
I don't think its unmetered air. The motor assembly is first rate, and I've looked everything over.
Thanks for the thoughts. It it coming if you have any others.
Last edited by mrfred; Jul 22, 2011 at 02:03 PM.
#11
EvoM Guru
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Perhaps could be the lack of "air shield", but I don't imagine that there are many people running a shield right now. I've got the MAF scaling set at 1.4x in the idle voltage range. Any more than that and I have to use unreasonably low latency values for the FIC1100s to get the STFT to fluctuate around 0%. The car feels good during off-idle transition. Thanks for the thoughts. It it coming if you have any others.
You can also try a non-linear approach to scaling the MAF in the lower Hz on the Primo. I've found I've had to do that on some of the Evos running the Primo. That's kind of what I meant when I said the Primo was a little "odd" there.
You said "any more then that" as far as scaling. I wouldn't add more, I would take out since the trims are negative.
I can't remember off the top of my head what Hz values represent what Trim cells (idle/cruise) but I would work in that idle Hz area, and even in transition to moving. That *might* be were the negative trims are coming from.
#12
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I'm running into a strange issue during my tuning of 3dman1's built Evo 10. We've had three different sets of injectors in that car. I meticulously dial in the fuel trims, he takes the car home for the night, and when I check the trims the next day, the idle trim is at or near -12.5%. Anyone who has dialed in injectors knows that its very obvious when the idle trim is off by that much, and yet when I was tuning the injector settings, I had the STFT perfect at idle, and the idle trim would typically hold near 0% for 30 minutes of stop-and-go driving. All tuning was done with Access Tuner Race.
I have no idea of the cause, but I keep getting a gut feeling that its something some sort of error in engine control algorithm that reports the fuel trims. Curious if anyone else has seen this.
I have no idea of the cause, but I keep getting a gut feeling that its something some sort of error in engine control algorithm that reports the fuel trims. Curious if anyone else has seen this.
-Matt
#14
I'm going to have 3dman1 double check for intake leaks.
#15
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whats going on with the battery voltage under long idle? Does he have a mini battery? If the voltage is dropping off, or.... going up after he drives the car a bit and the battery gets back to full juice........ Saw this on a megasquirt e30 i tuned for a friend of mine who had a "racing" alternator that only charged under higher rpm usage.