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Thread: no fuel trims at WOT? newbie needs help

  1. #1
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    no fuel trims at WOT? newbie needs help

    Hello,
    I have a 2000 5.3 swapped into a 1971 C10 with an SM465 manual trans. Engine is stock except for a CAI and shorty headers. My neighbor and i got it running on our own.

    I have been struggling with a stumbling under load issue. It will throw a P0507(idle higher than expected) and multiple misfire code. I have been chasing fuel, sensors, etc but i guess i just don't know enough to figure out what is going on. It ran great for 2 days in the midst of my troubleshooting but has since returned to it's troubled ways.

    Attached is my tune and a log of me hitting it at WOT. We noticed that the STFT and LTFT both go to 0.0 at WOT. Is this normal? Does anyone see anything else that i should be aware of?

    I really appreciate any help.
    Attached Files Attached Files

  2. #2
    Tuning Addict 5FDP's Avatar
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    GM runs narrowband sensors in these vehicles, the fuel trims generally only work in closed loop. Going wide open throttle enters open loop power enrichment and the fuel trims stop working. In some applications there is a STFT open loop function but does not work when the fuel system status goes to OpenLoop/Acceleration.


    Something I want to point out and this is very important. You say you bought a 2000 5.3 engine, so I want to assume that is correct and that everything else from a 2000 model year as well. Like sensors, injectors etc etc.

    The problem is that you are running a 1999 calibration file. There is a different between 1999 and 2000 for various airflow model settings, timing settings and injector information. 1999 trucks run smaller injectors than 2000+ model year trucks. So that is a issue and could cause you minor problems because the calibration information is wrong for the parts the truck is actually running.

    If that above information is true you will want to find a 2000 model year calibration file from the tune repository on your customer page. Make sure it's another stock 5.3 file like yours. Then copy over the stock information and see how much better it gets.

    Once you have the other stock file open it using the compare feature in the editor. Once you have both files open in the compare feature, click compare again. Then click view comparison log. In the new mini window collapse all the boxes, right click the engine icon and click copy over all difference. That will now have copied the information into your 1999 computer to make it run like a 2000 calibration.

    Other things to verify with swaps is vacuum leaks and fuel pressure. You need 58psi.


    Add knock retard, cylinder airmass, commanded AFR, injector pulse width avg and anything else you think you need to log in the main channels list on the left.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  3. #3
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    Quote Originally Posted by 5FDP View Post
    GM runs narrowband sensors in these vehicles, the fuel trims generally only work in closed loop. Going wide open throttle enters open loop power enrichment and the fuel trims stop working. In some applications there is a STFT open loop function but does not work when the fuel system status goes to OpenLoop/Acceleration.


    Something I want to point out and this is very important. You say you bought a 2000 5.3 engine, so I want to assume that is correct and that everything else from a 2000 model year as well. Like sensors, injectors etc etc.

    The problem is that you are running a 1999 calibration file. There is a different between 1999 and 2000 for various airflow model settings, timing settings and injector information. 1999 trucks run smaller injectors than 2000+ model year trucks. So that is a issue and could cause you minor problems because the calibration information is wrong for the parts the truck is actually running.

    If that above information is true you will want to find a 2000 model year calibration file from the tune repository on your customer page. Make sure it's another stock 5.3 file like yours. Then copy over the stock information and see how much better it gets.

    Once you have the other stock file open it using the compare feature in the editor. Once you have both files open in the compare feature, click compare again. Then click view comparison log. In the new mini window collapse all the boxes, right click the engine icon and click copy over all difference. That will now have copied the information into your 1999 computer to make it run like a 2000 calibration.

    Other things to verify with swaps is vacuum leaks and fuel pressure. You need 58psi.


    Add knock retard, cylinder airmass, commanded AFR, injector pulse width avg and anything else you think you need to log in the main channels list on the left.
    Thank you for all of this information. Knowing this information about the 99-2000 issue i can further tell you this:
    the harness, injectors, throttle body, 02 sensors, etc are all from a 2000 GMC sierra with a 6.0 That motor wouldnt work with the crank it had, so i traded the engine with a buddy for the 5.3. We kept the ECUs with the motors.

    so i am running all 2000 6.0 sensors, harness and such with a 5.3 motor and ecu.

    If what youre saying is true then i have a mess on my hands. I will follow your advice and work on changing the tune accordingly.

    I will reply back with my findings.

    All that said i intend to try to find a 2000 6.0 tune since that is what all of my sensors and wiring is for. Sound right?

  4. #4
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    here are my changes and results. It ran poorly and threw a bunch of misfire codes pretty quick.
    Attached Files Attached Files

  5. #5
    Tuning Addict 5FDP's Avatar
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    The 5.3's and 6.0 from 2000 run the same sensors and injectors. Changing the calibration information to a 5.3 from 2000 will still work fine.

    If you have misfires, you'll have to do real world checks then. Verify you have no vacuum leaks, make sure fuel pressure is not dropping. There can be zero exhaust leaks pre-o2 sensor and or directly after the sensor either. Check the spark plugs and wires. Use the scanner to pull up exactly what cylinders are misfiring and see what you can do. If that means swapping plugs with another cylinder to see if it follows, or swapping a coil pack side to side.

    Worst case is that a cylinder has low compression if it kept misfiring.

    Based on the log something is up with drivers side bank one, at idle the long term fuel trims creep up to 11 and later on in the log it went all the way to the max of +25 where as bank 2 does not go that high. I'm sure the more its run the more the long term fuel trims would learn and you'd see where they really end up.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  6. #6
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    I agree that real world work is needed. It 'miraculously' ran great for 2 days recently then faded back to poop. So I will re do my due diligence. Thank you again.