AlwaysinBoost

iTrader: (17)

Now I have no clue what is happening. I haven't changed anything since last night. This morning when i drove to work the fuel trims were in check as far as I could tell. However after work I started the car up and my STFT went to -25% and the A/F gauge was showing 11.x:1!

It seems to drive fine, the STFTs at part throttle are between -3% & 3%. Its only while I'm @ idle does things get screwy.

Why would the car run fine this morning, after sitting all night, and on my lunch break, but when I go to drive home the idle is all screwed up...

AlwaysinBoost

iTrader: (17)

to confuse things even further... with the same settings which I haven't changed since Sunday I'm now getting readings of 15-18% for the STFT @ idle. My LTFT are between -9 & -11%.

the 15-18% STFT at idle now is telling me I need to ADD fuel, but why the sudden change from what it was reading yesterday??

Does anyone have an explaniation or answers? I'll take even an educated guess at this point... I just don't want to make any changes until I know where to look for problems.

l2r99gst

iTrader: (2)

I haven't really followed all of your threads, but I'll throw in a few comments:

Don't worry too much about the STFT....that will jump around a lot and the STFT will be eventually merged into the LTFT.

Your LTFT will tell you your state of tune in regards to the fuel trims. So, pay more attention to your LTFT. Your STFT is just there to compensate for varying conditions, etc, on a short term basis. If these conditions occur over a wide enough period of time, they get moved into the LTFT.


Eric

AlwaysinBoost

iTrader: (17)

Thanks Eric, that makes me feel a little better. I felt like I was a cat running after its tail.

My LTFT's are between -8% & -11%, so how should i remove fuel to conpensate? Injector voltage latency, injector scaling, or via the high octain map.

I should point out that my stft while crusing are pretty good still, between -3% & 3% or close to around there...

thanks.

l2r99gst

iTrader: (2)

Well, that sort of matters if your LTFT is the same at idle and cruise. Is your between -8 and -11 at both idle and cruise, or is it one or the other. If it is one or the other, what is your LTFT at idle and what is your LTFT at cruise.

Some people don't realize that the ECU uses a different LTFT at idle and cruise. And to tell you the truth I haven't even looked at how EvoScan has them setup for logging.

If they are both the same, I would personally use your injector scaling to compensate. That would increase both trims, but this would also affect the rest of your fueling map. In my opinion, this is the correct way, but it takes the most time.

You can try injector latencies, too, but if these latencies work like the deadtime value, changing these will affect your idle LTFT twice as much as your cruise LTFT, since the IPW at cruise is roughly twice that at idle.

So, to sum it all up, check what your LTFT is at cruise after a nice long steady cruise, like 15 minutes of same RPM on the highway. Then idle for 10-15 minutes. Record what each LTFT is. If they are both the same, use the injector scaling and fix your map, too, based on your correction. If they are not the same, you can use the injector latencies to match them up, then you can use the injector scaling to get them to 0.

I can try to help out some more after you post the numbers. I will try to explain what I mean a little more, too. I think I may have explained this in a post about fuel trims in this forum before. Maybe we can search for what I wrote, so I don't have to type this again.


Eric

MalibuJack

iTrader: (5)

Evoscan has them the same way my logger is (only I use scaling that is identical to a regular OBD-II which means 0% is perfect, and it can range from -25 to +25%

Anyway..

There is the O2 Feedback (That is your short term fuel trim)
FuelTrim Low
FuelTrim Mid
FuelTrim High

THe low is your Idle long term fuel trim
Mid is your cruise long term fuel trim

High doesnt ever seem to change, it might have something to do with high load conditions such as A/C and whatnot.. but I haven't done enough to verify that..

This is where graphing becomes really useful, since you can take a long drive in stop and go traffic, and a cruise on the highway, and a few WOT pulls, and watch things as your fuel trims, O2 feedback, Knock count, Load, etc..

BTW If you need to figure out what load cells to tune use the 1C value for load, not the calculated load, since calculated load will always hover around 20% in closed loop fueling..

AlwaysinBoost

iTrader: (17)

I believe I have read your posts about fueling before, but I'm the type of person who can only learn by doing, not reading, so it didn't make sense to me then.

The LTFT #'s I quoted (-8% thru -11%) were at idle, my STFT @ idle is 15-18% when my A/F is at 14.7:1. I'm not 100% sure what my LTFT while crusing are because I was focusing more on my STFT number which were between -3% & 3%. I want to say the LTFT while crusing was around -6% but I'm not 100% sure...

MalibuJack

iTrader: (5)

I decided to do some quick analysis to see a few things..

You can log data while driving, and get a much better indication by looking at the different trims and see how they change, that might give you an indication..

On my car, ECULoad and Calculated load are different, that leads me to believe that my MAF calibration needs to be adjusted a little more (as a side note)

FWIW, this is where the real tuning is.. Anyone can make peak numbers on a dyno in a clean pass with no knock.. But building a map that has very little knock, and works well under varying load and driving conditions is where the magic is..

AlwaysinBoost

iTrader: (17)

thats exactly what I have been doing, but I don't use EVOScan during the day just because I don't want to leave the laptop in my car, I use pocketlogger & a PDA to monitor my fuel trims.

evoteddy111

iTrader: (5)

bump

AlwaysinBoost

iTrader: (17)

ok, I hope this helps diagnose my problem. I took a nice long drive and my trims were pretty consistant...

idle:
STFT: 17%-18% when A/F is @ 14.7:1
LTFT: between -9% & -11%

light driving/crusing:
STFT: -3% to 3% (roughy)
LTFT: -6%

l2r99gst

iTrader: (2)

First off, something that concerns me a little is that you mention that your STFT at idle is +17-18%. Do you mean that when you idle for 10 minutes or so, the STFT just stays at around +17-18%? I wouldn't think so, since this number should be pushed into the LTFT. If you idle long enough, your STFT should go to bouncing around 0. Then you look at what your LTFT is. The STFT may be bouncing around a lot though, especially when the fan kicks on, etc. That's fine....just wait til they look like they average about 0, then look at the LTFT. Same for crusie, but it looks like you are there already.

OK, now, for the sake of discussion, I will explain how to scale your injectors and fuel map to get both LTFT to zero, assuming that your idle STFT was averaging about 0%. This will not apply if your idle STFT really is averaging about +17-18% at this time. But, the advice below will still hold true for a new idle LTFT. Just adjust for the new numbers accordingly or post again.

OK, the LTFTs at idle an cruise are close enough that I don't think you have to mess around with the latencies. You can if you want to fine tune a bit more, but I would do this:

Rescale your injector to be 8% bigger than what you have them at now. That will cause the ECU to shorten the IPW by 8% so in effect you are taking out 8% fuel, which is what your trims are doing right now. That should bring your LTFT for idle to about -2% and your LTFT for cruise to about +2%. That would OK in my book, as you have plenty of adjustment in either direction for both trims.

But, since you're scaling your injectors bigger, this will also lean out the your open loop fueling maps by about 8%, too. So, to get all of your A:F ratios back to what they are now at WOT, you would have to edit your open loop fuel maps so the values are also 8% richer. For example, if you have a a value of 14.0 in a certain cell, you would have to change that to be .92(14)=12.88.

Out of curiosity, do your wideband values currently show richer than what are in your open loop fuel map cells? For example, does your wideband read like 12 when your cells are 13?

Again, let me know what your ltft is at idle when your stfts are bouncing around 0 and I can give you a more definitive answer on exactly what needs to be done.

Eric


Note: Never rescale your injectors bigger or mess with the open loop fueling map without the use of a wideband. I am assuming that you have one.

AlwaysinBoost

iTrader: (17)

Great post Eric. I'm going to let me car idle again for a good 10-15 minutes and use those LTFT #'s, then go for a 10-15min cruise on the highway to get some good LTFT #'s and adjust the scaling accordingly

EVOtagger

iTrader: (33)

great info in here

MalibuJack

iTrader: (5)

Short term fuel trims are really just "additions or subtractions" from the long term fuel trims.. Which means if your running really rich, or running really lean, then both your short term and long term values might be pegged because there is no longer any adjustment the ECU can make. Then it resets, and starts over, and you see the symptoms of what your describing.. If the car wants to always be at 14.7 and it cant.. then all of the trims will be maxed or nearly maxed..

Just like said before..

The short term trims should always swing back and forth around 3-5% (+/-) occasionally at part throttle driving and throttle inputs, it may go more.. If it does, then the long term trims will adjust accordingly to try to reduce that.