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.

 

Are you using the new BETA version of ATR?

 

Yes, but I saw it in all previous versions of ATR that I used as well.

 

OEM MAF housing or other?

Open Filter?

 

its a primo intake with 3.5 maf

 

Are you still using the infamous FIC 1680's as well? Any apparent issues like others are having?

 

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).

 

It might be MAF scaling issue.

If not there is unmeter air getting and the ECU is dumping fuel and then trying to over correct it. I would look over the MAF scaling.

 

Could be that.

I'd also look at the MAF scaling in the idle and lower HZ. I've noticed the primo intake is a little "odd" in that area and on transition.

 

MAF scaling is good. 1.4x in the idle voltage cells and transitioning to 1.5x from cruise on up to full throttle. Nice smooth transition from 1.4x - 1.5x. Injector latency and scaling values are exactly where they should be for FIC1100s.

I don't think its unmetered air. The motor assembly is first rate, and I've looked everything over.

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.

 

Yea I have trim swings on warmer days, running an AEM intake currently without the airbox. Nothing as extreme as this, but the primo size might be more sensitive to it.

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.

 

Check his coupler from the intake pipe to the turbo and make sure its clamped securely. Car had the same injectors and was baffled as it was giving us the same exact issue that your describing. Hope this helps!

-Matt

 

what if you let the car idle for an extended period of time (ie 5 mins after start) what does the STFT do?

 

I'll have to look again, but recollection is that sometimes the idle trim will hold steady, and other times the same issue will appear and the idle trim will start going negative even though the STFT is where it should be.

I'm going to have 3dman1 double check for intake leaks.

 

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.