I recently installed my VT engines built motor (as well as many other parts) last week (pictures are to follow soon) and everything is running perfectly. I am just curious as to what are good LTFT values. What type of values should I aim for with my datalogger? Here is my current set up:

Accel 36 lb injectors

Vortech SFMU - Hard Spring, 2.62 disk, Idle Pressure 18 lbs

STFT at idle - Hangs around 0 for a majority (90%) of the time. Every once in a while it will go to -4 to +3 for a short period of time which I believe is fine as the car is adjusting the amount of fuel.

LTFT at idle - Hangs around 17 (I can't remember if it was positive or negative...need to datalog again as my batteries died).


Please let me know what I should be seeing for the LTFT. I believe my STFT is very good as it should be as close to zero as possible to allow for maximum adjustment.


Thanks,
Kurt

Here's a quote from Corbins website...I hope this is what you looking for:

"You want it to be well below 25%. Lets say 15% or less. If it ever reaches 25%, the short term trim will have to start compensating for the maxed out long term trim. In addition, the fuel map for the stock ECU tops out around 0 psi boost. When you go beyond the range of the stock ECU fuel map, it will stop adjusting long term fuel trim. For example: If you were at -17% long term trim around 0 psi boost, the long term trim will stay at -17% as long as you are above 0 psi boost, NO MATTER WHAT your fuel needs are. If your long term trim is maxed out and locked, the short term trim may have to compensate for this, ruining its ability to react to changing engine conditions. Short term trim will continue to adjust even if you go beyond the range of the stock ECU fuel map. Once you verify that your long term trim is acceptable at 0 psi boost, you can continue."

getty up

-kent-




'98 Talon...gone, but not forgotten

Don't be too concerned with LTFT,its basically a byproduct of STFT. Your STFT is what you should concentrate on. You have 25% of instantaneous fuel correction, +25% means the ECU is richening out, 25% of the injector duty cycle, and -25% means its leaning out 25%. In a perfect world, you want your STFT to stay around 0, but you do have 25% correction BOTH ways for ECU fuel compensation. Just because you may see your STFT at -15%, doesnt mean your are running rich. Its just saying the ECU is trying to cut fuel by that much. The only time you will actally run rich, is when your STFT is pegged at -25%. The downfall to that, is the ECU cannot adjust fuel anymore to lean out, and you will throw a too rich CEL, and you will indeed run rich. The closer you keep the STFT to 0, the more room you give the ECU to adjust fuel. If you can only keep your STFT to -20% and no lower, that is ok, but it really means you are running on the edge of ECU fuel adjustability, but you still dont run "rich". LTFT is the effect of where the STFT is, over a longer time frame. When you run larger than stock injectors, it becomes hard to get your LTFT close to 0. In order to do this, you need to get your STFT to go into the positive numbers, frequently, as that will start to drive down your LTFT, The longer you STFT stays in the negative, the higher your LTFT will be. Make sense? If you say your STFT goes from low positives to low negatives, then you are right on the money

LTFT is basically telling you how long your STFT has either been cutting fuel, or adding fuel. (-numbers/+numbers). If your STFT goes into the negatives more frequently than it does the positives,then that will raise up your LTFT into the negatives, and vice versa.

13.5 @108 MPH-2.2 60ft(stupid FWD!)
S16G @ 18 PSI/FMIC/Running on MegaSquirt II (Now with sequential
fuel injection)
My webpage: http://eclipsed4evr.home.comcast.net
-1998 Mitsubishi Eclipse RS-T- "Toy"
-1992 Plymouth Laser Turbo AWD(SOLD)
-2000 Honda CR-V(daily)

Thanks guys. I thought I read posts before where it said to only concentrate on your STFT and ignore the LTFT. I was pretty sure that you are to set up your STFT for instant ECU adjustment/correction which would be keeping the STFT as close to 0 as possible or within the -5/+5 range. I just wanted to double check before I mess something up as all this equipment isn't cheap and I don't want to be doing it again in a short period of time. Now all I need to do is get used to the CM Stage 4 clutch and I'll be set. I appreciate all the help and will be posting some pictures soon.

Thanks again,
Kurt

One last question. I went outside to start my car this morning and it was the coldest it has been outside so far this year - 36 degrees. The car started fine but during it's initial warmup the engine sputtered (dropped to real low rpms and almost stalled). I slightly depressed the gas to save it from stalling. Once the car warmed up, it idled perfectly. I was datalogging during this and I saw the STFT jump to -11 and then came back down to -5. Once the car warmed up, it settled back down to hovering around 0. I double checked the STFT after getting to work - about a 20 min drive - and it was right at zero. Are these type of starts a characteristic of the larger injectors? I would assume it is as the engine is designed to run a little richer on a cold start. Am I correct?

Thanks,
Kurt

yeah...warm up is open loop. I believe that once the coolant temp reaches certain a temp the ECU switches to closed loop. When I'm warming up my car I always wait at least until the car goes into closed loop before I take off...then I'm real gentle with her until the temp gauge gets up to normal operating temp. DOn't want to take any chances. But it's never almost stalled on me...it rolls over once or twice more then it used to on start up but I don't notice any change in idle over stock.

getty up

-kent-




'98 Talon...gone, but not forgotten

Yeah, my car will so the same thing when cold. I have noticed, that the ECU will go into closed loop, when the o2 sensor heats up, which looking at my EGT gauge, happens around 800-900 degrees. Coolant temp has a role in this too, as stated by Kent.

13.5 @108 MPH-2.2 60ft(stupid FWD!)
S16G @ 18 PSI/FMIC/Running on MegaSquirt II (Now with sequential
fuel injection)
My webpage: http://eclipsed4evr.home.comcast.net
-1998 Mitsubishi Eclipse RS-T- "Toy"
-1992 Plymouth Laser Turbo AWD(SOLD)
-2000 Honda CR-V(daily)

Thanks for all the info. I just wanted to see if this was *normal* for those who run larger injectors. I think I am just paranoid that I did something wrong during the swap as everything went so perfect. It was also something that the car never did in the past but as soon as the car warmed up and fought through the first few seconds of closed loop mode it idled perfectly.

Thanks,
Kurt