Closed Loop Fuel Trims at idle & low rpms

Smogrunner · Apr 28, 2006, 12:15 PM

If the stock ecu is making significant adjustments to the long term fuel trims (pulling fuel due to larger injectors, for example) but is still within its adjustment range, is drivability affected in any way? At what level of fuel trim adjustment does a car start running poorly?

trinydex · Apr 30, 2006, 12:50 AM

the ecu's closed loop adjustments are afr targeted (you prolly know this already), the ecu aims for stoich at low throttle/closed loop operation. just becuase it aims for it doesn't mean it hits it however, in fact it's ALWAYS cycling AROUND it.

now with that said the closed loop adjustments are VERY adapting and are only outdone by injectors that are too large. i think something in the vicinity of 780 even WITH corrections from an afc will run rather ruff. some people with maftpro, xede and ecu+ have had _minor_ injector scaling issues. i do realize that injector scaling is just an overall % reduction of fueling but it does not hide the fact that if you go to big... you will have problems, even with our industry's best piggybacks.

with that said it's nice to add that dynoflash had problems scaling 780s with a flash. if that's the case... then it truly is a limitation of the ecu!

TURBODAWG · May 2, 2006, 07:57 AM

Someone I know has NO problem scaling injectors up to 880 cc with the stock ECU. It helps if you know how to adjust the dead time in the stock ECU as well.

Brian

trinydex · May 2, 2006, 07:24 PM

mm in that case which injector size do you feel is the limit? cuz the problem is i haven not heard of too may people running above 780

TURBODAWG · May 2, 2006, 07:39 PM

The reason why you havent heard of many people running larger injectors is because only one tuner has the ability to change the needed parameters in the ECU. I was told that 880's are about the limit. 1000 cc injectors are untested with the stock ECU on an Evo. They might be possible, depending on the quality of the injectors.

Brian

jj_008 · May 2, 2006, 09:53 PM

Shiv can scale 880cc injectors so I am sure others can do the same (if they know how).

trinydex · May 3, 2006, 01:11 AM

who's that?

8URVTEC · May 3, 2006, 02:56 AM

Richard Garcia at Dynocomp (Scottsdale) scaled my 1000cc AMS when I had them with Ecutek program.

trinydex · May 3, 2006, 07:07 AM

hey so can someone give me an overview of how the ecutek or techtom softwares deal with rescaling. i'm under the impression there is actually a function in the software specifically to address this. so how does it work? is it the same as a global open loop reduction in fueling? because on the other hand it really doesn't _sound_ that simple.

TURBODAWG · May 3, 2006, 07:43 AM

Quote:

Originally Posted by jj_008

Shiv can scale 880cc injectors so I am sure others can do the same (if they know how).

Can Shiv scale the injectors in the ECU itself or throught the XEDE piggyback? If he has the ability to scale the 880cc injectors with the XEDEflash itself, then he is another tuner that can do that. I am not talking about globally going in a reducing all the fuel maps, but fixing ONE variable that accounts for the larger injectors. But the key to doing it correctly, is being able to adjust the dead time in the stock ECU as well, which is also a variable.

Brian

Smogrunner · May 3, 2006, 07:48 AM

Shiv uses the the ecu to rescale injectors. How exactly he does it I'm not sure, but he did a great job on my 880s.

l2r99gst · May 3, 2006, 08:49 AM

Quote:

Originally Posted by Smogrunner

Shiv uses the the ecu to rescale injectors. How exactly he does it I'm not sure, but he did a great job on my 880s.

Any tuner should know how to do this. In fact, I believe the offsets are posted in the EvoFlash thread or on the openecu forums.

Anyway, to answer the first question, I will give you my expriences with the DSM ECU. Until I jump into the Evo ECU, I can't answer this specifically for the Evo, but I would imagine this area to be similar if not exactly the same.

For the DSM ECU, fuel trims had an adjustment range of -12.5 to +12.5 %. Obviously you wanted the LTFTs as close to zero as possible so that the ECU could use it's adjustment range, but as long as you were within that range, your closed loop drivability would not be affected. The short term fuel trim (STFT) would compensate for any immediate changes that were necessary to cycle around the narrowband O2 .5V reading (stoich).

The issue where you may have some drivability comes in the transition area of closed loop to open loop. Fuel trims are not applied to open-loop fueling. These are where the internal fuel maps are used in the ECU. So, if you had close loop fuel trims that were near or at either extreme of adjustability, then when you transition to open-loop fueling, you won't have a smooth transition of AFRs as you might want.

It's a bit hard to explain, but I hope that made sense. Basically, fuel trims do matter, even though they aren't applied during WOT (open-loop) fueling.

Eric

trinydex · May 3, 2006, 01:32 PM

how much range does the stft have?

l2r99gst · May 3, 2006, 02:00 PM

Quote:

Originally Posted by trinydex

how much range does the stft have?

You know, I don't remember off the top of my head. But, the range of the STFT really doesn't matter too much. Whatever the STFT is doing, that will eventualyl be translated into the LTFT.

For example, if you just reset your battery, your LTFT would reset back to 0. Well, let's say that before you reset your batter your idle LTFT was at -5%. After the reset, the idle LTFT would be at 0% and the STFT would be jumping around -5%, until this change was pushed over to the LTFT. Eventually (usually about 10-15 minutes of a constant idle) the idle LTFT would then change to -5% and the STFT would be bouncing around 0.

The STFT is just there to do immediate adjustments based off the o2 sensor, to keep the O2 voltage bouncing around .5V (stoich).

Eric

SuperHatch · Jun 5, 2006, 09:12 AM

Here's a question for you all...

My current settings for my 780cc injectors are a dead time of 300 and a global reduction in fueling of -40%...

They were originally 315 and -40%, but the idle fuel trims were lower than my cruise fuel trims. I know that reducing the dead time will help bring the two fuel trims closer together. I reduced the dead time to 300 and the trims are closer but still not the same. I am going to continue to log and alter the dead time until the trims match.

However, I am getting the trims to match at +8%. Does that mean that I then have to change my global fuel adjustment to -48% or -32%???

I understand that altering my global adjustment will then require a retune of the WOT fueling, but I want to get the base fueling right before I mess with anything else.

- Steve