Fuel trims - CamaroZ28.Com Message Board


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Old 10-03-2017, 07:59 PM   #1
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Fuel trims

What would cause STFT on bank one to be much higher (positive 20 to 30%) than on bank two?
Bank two will be negatives about 10% but go away under throttle.
Bank one will continuously show positive fuel (lean) on bank 1 and doesn't get much better just kinda hangs there.

Activated the LTFT I'm going to log tomorrow.

Things I've changed.
02 sensor bank 1
Compression good all around
Injectors tested good.

I do have low vacuum, I'm unsure what the vac for a cam with 110 lsa should be 234/244

Lt1 car with 24x ...

I'm gonna change the oxygen sensor extension also. Sometimes my trim on bank one tends to be slow and it likes to hang low in the milivolts . Then start acting "normal."

But what would cause side specific issues.
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Old 10-03-2017, 11:34 PM   #2
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Re: Fuel trims

When you look at fuel trims, you need to know which "fuel trim cell" the PCM is operating in (16 cells in a rectangular grid defined by RPM and engine load, represented by MAP]. Couple more cells (17 and 18) for accel, decel under various conditions. For each cell, there is a stored LTFT (left and right) and dynamic (constantly moving up and down) values for STFT (left and right). So your log needs a continuous record of cell, LTFT-L, LTFT-R, STFT-L, and STFT-R. Other data needed includes O2-L, O2-R, MAP, and throttle position percent.

Looking at the STFT's without the other data is meaningless. And looking at a single frame of data makes it even less useful if that is possible. The system is updating about 9 times per second. The PCM is constantly toggling the STFT's between rich and lean in closed loop, because that's what allows the cats to work (still works that way whether you have cats or not). Most data loggers don't seem to record more than 6 or 7 per second, but a continuous log over a period of minutes is very useful.

And the 16 cells are for the LT1 PCM. The LSx PCM used w/ 24X just adds even more cells and complication.

Last edited by Injuneer; 10-03-2017 at 11:37 PM.
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Old 10-06-2017, 03:14 PM   #3
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Re: Fuel trims

Injuneer what other data do u need.

I actually figured out that bc of the ls1 pcm the .67idle voltage was to high. So I adjusted it. The STFT seem to have leveled out for the most part.
I did manage to get a minute ot LTFT data and pass is good driver side is about 20% adding.
When I blip the throttle at the LTFT will level out but when it gets back to idle it's back to 20% adding.
Ideas?
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Old 10-06-2017, 03:18 PM   #4
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Re: Fuel trims

Injuneer what other data do u need.

I actually figured out that bc of the ls1 pcm the .67idle voltage was to high. So I adjusted it. The STFT seem to have leveled out for the most part.
I did manage to get a minute ot LTFT data and pass is good driver side is about 20% adding.
When I blip the throttle at the LTFT will level out but when it gets back to idle it's back to 20% adding.

also got a cps code now but I think it's due to a misfire. Not thesensor itself
Ideas?
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Old 10-06-2017, 05:03 PM   #5
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Re: Fuel trims

LTFT's and STFT's change when you move the throttle, because there is a grid of "cells" based on RPM and MAP (as explained above) with stored LTFT's. Move away from idle, and the numbers change. How much have you driven the car since the last PCM reset? Step on the throttle at idle, RPM increases, MAP show "no load" so you are in a cell you would very seldom actually drive in. LTFT could be near 0 at higher RPM, then as you let off the throttle, when RPM returns to the idle value, you go back to the idle cell with the very high LTFT. If the PCM can't add enough fuel using the LTFT, it starts using the STFT to eliminate the perceived lean condition. That's what appears to be happening on the driver side only. Again, based on the very limited data you have posted, which really makes it difficult to pin anything down, other than there is a problem.

You indicate you have a CPS code (which one?). Do you also actually have a misfire code? Because a misfire would explain the huge fuel corrections being made on the driver side. If on the driver side you have a +20% LTFT (1.2X multiplier) and a +30% STFT (1.3X multiplier) the PCM is reacting to lean O2 sensor readings by adding more than 55% extra fuel on that side (1.20 x 1.30 = 1.56) - Misfire on driver side, plugged injector on driver side, huge vacuum leak SPECIFIC to the driver side (not one that could affect both banks), faulty O2 sensor or sensor wiring.

Apparently the passenger side has no problem, given the fact you didn't point to a large + LTFT, and the fact the STFT is near 0%.

Vacuum will be low with that cam. Overlap goes up, vacuum at idle goes down. I would guess (assuming your location is near sea level) that you are seeing 10-12"Hg vacuum, or MAP in the range of 50-60 kPa. That can cause mixture problems at idle, with high blowthrough of A/F mixture when both valves are open, making the O2 sensor read lean with the unused air.

If you can produce a data log in either .csv or .xls format, I can look at it. I mentioned the minimum requirement in the CZ28.com post. The more items logged, the more you can learn. What software are you using?
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Old 10-06-2017, 05:35 PM   #6
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Re: Fuel trims

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Originally Posted by Injuneer View Post
LTFT's and STFT's change when you move the throttle, because there is a grid of "cells" based on RPM and MAP (as explained above) with stored LTFT's. Move away from idle, and the numbers change. How much have you driven the car since the last PCM reset? Step on the throttle at idle, RPM increases, MAP show "no load" so you are in a cell you would very seldom actually drive in. LTFT could be near 0 at higher RPM, then as you let off the throttle, when RPM returns to the idle value, you go back to the idle cell with the very high LTFT. If the PCM can't add enough fuel using the LTFT, it starts using the STFT to eliminate the perceived lean condition. That's what appears to be happening on the driver side only. Again, based on the very limited data you have posted, which really makes it difficult to pin anything down, other than there is a problem.

You indicate you have a CPS code (which one?). Do you also actually have a misfire code? Because a misfire would explain the huge fuel corrections being made on the driver side. If on the driver side you have a +20% LTFT (1.2X multiplier) and a +30% STFT (1.3X multiplier) the PCM is reacting to lean O2 sensor readings by adding more than 55% extra fuel on that side (1.20 x 1.30 = 1.56) - Misfire on driver side, plugged injector on driver side, huge vacuum leak SPECIFIC to the driver side (not one that could affect both banks), faulty O2 sensor or sensor wiring.

Apparently the passenger side has no problem, given the fact you didn't point to a large + LTFT, and the fact the STFT is near 0%.

Vacuum will be low with that cam. Overlap goes up, vacuum at idle goes down. I would guess (assuming your location is near sea level) that you are seeing 10-12"Hg vacuum, or MAP in the range of 50-60 kPa. That can cause mixture problems at idle, with high blowthrough of A/F mixture when both valves are open, making the O2 sensor read lean with the unused air.

If you can produce a data log in either .csv or .xls format, I can look at it. I mentioned the minimum requirement in the CZ28.com post. The more items logged, the more you can learn. What software are you using?
ok I just needed to know what you needed to help me get a better understanding of what's going on here.
Injectors were tested and good. Compression was good. New plugs and wires.
I use Hptuners and I have some logs and the tune if you would like.
I'm still trying to get an understanding on tuning also. Tho I have not tuned my own yet. It's been tuned tho by a local.

Forgot your questions l, the code is P0336 no misfire code, bunch of popping in the exhaust when at idle every so often.
I haven't driven it much. I adjusted the tps. Should I reset th r pcm?

Last edited by CamaroSS30thAnn; 10-06-2017 at 05:49 PM. Reason: Questions
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Old 10-06-2017, 05:39 PM   #7
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Re: Fuel trims

How do i link a file to here
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Old 10-06-2017, 08:32 PM   #8
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Re: Fuel trims

Quote:
Injectors were tested and good.
How were they tested... flow test?

To attach a file:

- click on "Go Advanced" button

- scroll down and click on "Manage Attachments"

- screen will open with "Choose File" buttons

- click one and browse to file location

You can attach .csv and .xls files as large as 5 MB

I'm not a tuner, at least not beyond my own car. So no need to send me the tune.
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Old 10-06-2017, 09:00 PM   #9
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Re: Fuel trims

  1. Quote:
    Originally Posted by CamaroSS30thAnn View Post
    How do i link a file to here

Quote:
Originally Posted by Injuneer View Post
How were they tested... flow test?

To attach a file:

- click on "Go Advanced" button

- scroll down and click on "Manage Attachments"

- screen will open with "Choose File" buttons

- click one and browse to file location

You can attach .csv and .xls files as large as 5 MB

I'm not a tuner, at least not beyond my own car. So no need to send me the tune.

Ic. I couldn't find it using the mobile app But I got it. And yes flow tested
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Old 10-06-2017, 09:10 PM   #10
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Re: Fuel trims

Quote:
Originally Posted by Injuneer View Post
How were they tested... flow test?

To attach a file:

- click on "Go Advanced" button

- scroll down and click on "Manage Attachments"

- screen will open with "Choose File" buttons

- click one and browse to file location

You can attach .csv and .xls files as large as 5 MB

I'm not a tuner, at least not beyond my own car. So no need to send me the tune.
Camaro16 was an older file I can get another of need be
Camaro21 was today..
Attached Files
File Type: hpl camaro16(1).hpl (703.7 KB, 6 views)
File Type: hpl CAMAro21(1).hpl (69.1 KB, 4 views)
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Old 10-07-2017, 11:20 AM   #11
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Re: Fuel trims

Have no idea how to open HPTuner files. Most scan programs offer the option of exporting in .csv or .xls format. Tried opening it with Excel, but just ended up with a bunch of jibberish.
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Old 10-07-2017, 12:12 PM   #12
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Re: Fuel trims

15 was some driving around and idle.
21 was a weird one after I changed back to stock throttle body couldn't get it to idle.
22 was back to the holley but switched to .55 idle tps
I got a crank code on 22 . Mostly idle time
Attached Files
File Type: csv camaro21.csv (3.53 MB, 4 views)
File Type: csv camaro22.csv (307.8 KB, 4 views)
File Type: csv camaro15.csv (3.25 MB, 5 views)
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Old 10-07-2017, 04:47 PM   #13
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Re: Fuel trims

I downloaded all three and opened them. Definitely different than what you see in an LT1 log. All three go into closed loop, but two of them only use STFT for the entire log. All LTFT's are 0. In places, there are huge STFT numbers like +25 (driver) and -20% (passenger). Net difference in fuel trims is above 30% for a huge part of the time. The differences do disappear as engine load/RPM increase.

I'll see if I can identify a cause for the weird numbers. I didn't see a "cell" number in any of them. Should be available, it's listed in the parameters in the 2000 factory manual for the LS1 PCM. Not sure how that compares to the PCM you are using.
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Old 10-07-2017, 07:55 PM   #14
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Re: Fuel trims

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Originally Posted by Injuneer View Post
I downloaded all three and opened them. Definitely different than what you see in an LT1 log. All three go into closed loop, but two of them only use STFT for the entire log. All LTFT's are 0. In places, there are huge STFT numbers like +25 (driver) and -20% (passenger). Net difference in fuel trims is above 30% for a huge part of the time. The differences do disappear as engine load/RPM increase.

I'll see if I can identify a cause for the weird numbers. I didn't see a "cell" number in any of them. Should be available, it's listed in the parameters in the 2000 factory manual for the LS1 PCM. Not sure how that compares to the PCM you are using.
Yeah the first two i didn't have the LTFT active which is annoying bc they are needed in this case.
The last one had LTFT but it was only for a minute and mostly idle time.
The last log I adjusted the tps to .55 and the stft seemed to be better but I didn't get much log time in closed loop bc at idle The exhaust would pop from I'm assuming unburnt fuel and I was worried the neighbours would call cops on me again.
The LTFT on that one was also at 20% positive but would go away under small blips of the throttle
I didn't see a change in the stft which were mostly 0 which was odd bc they usually changw real fast.
The pcm I'm using is your base 0411 pcm just modified by torqhead to use the stock lt1 harness.
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Old 10-07-2017, 08:03 PM   #15
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Re: Fuel trims

Are u thinking this is on the tune?
It's also throwing a p0336. But unsure was to y yet
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