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Thread: 4l80e TCC problem

  1. #1
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    Default 4l80e TCC problem

    I have been having terrible detonation at low RPM recently and found the culprit. My TC is locking as soon as the trans hits 2nd gear and remaining locked despite my attempts to keep it unlocked by setting the apply MPH tables to 255mph in every gear. I also set the TPS unlock tables to 5% across the board and the converter will not unlock even with 40% TPS. I ran into similar problems in another truck with the converter not responding to any input from the flash. The vehicle is a 2005 GMC 2500 (4l80e) truck. I have logs available and a calibration file if it will be useful.
    Thanks in advance,
    Henry

  2. #2
    Joe (Moderator) joecar's Avatar
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    Stoichiometric/Henry, welcome to the forum...

    Post your tune file if that's ok.

  3. #3
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    Sorry joecar, but I jumped the gun on this one. I was misreading the 'enabled' thinking it said 'locked' on the scan. I made some changes to get the converter to actually lock and could see 'locked' and feel the difference.

    I still get knock at low RPM with the converter unlocked. I have a few log files and a tune that it was running on. If I should post this in another section since it is not trans related let me know.

    Thank you and sorry for the mix-up.
    Attached Files Attached Files

  4. #4
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    Those two log files don't show the full amount of knock that I get. I was running the stock MAF for about 6 months before this happened with no problems. I recently changed to a 2bar SD custom OS and started logging for the VE when I started getting knock. I added fuel in the areas that I suspected were lean, but I still had knock when running ~2000rpm at 12:1 AFR on the WBO2 at 30-40% TPS. I have since been unable to tune out the knock after pulling 10* or more of timing out of the tune. I suspected bad gas, but re-filled with new 91 (highest at pump here) and the problem persisted. I checked the injectors, cats, plugs, wires and all were in perfect shape.

  5. #5
    Joe (Moderator) joecar's Avatar
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    Hmmm...

    Can you hear the knock when it happens...?

    Also check for oil being sucked thru PCV plumbing into intake manifold (this will lower the octane number of the fuel:air charge and may allow knock).

    91... you must be in Calif.

    Set A0001, A0002 to in-range values (set them to max-1, save file, exit tune tool, reopen tune tool and file, set them to max, save file).

  6. #6
    Joe (Moderator) joecar's Avatar
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    Let's move this thread to FI & NO2...

  7. #7
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    I'll fix the two values first thing.

    I do not have the PCV hooked to the intake manifold, no chance of oil getting in.

    The whole story behind this is, I recently made some changes to the truck (2005 GMC 6.0L with Magnacharger) including a 2bar map sensor. I scaled the map sensor and drove the truck for about a week without issues, still running on the MAF.

    I then removed the MAF and started tuning for SD. I started having problems with audible knock in different areas and I attributed it to the VE being inaccurate and having lean spots. I reduced the timing tables ~5 degrees across the board. I got the VE closer that where it was and still had trouble with knock, I pulled more timing. The knock continued and I began to log negative timing in areas due to the 8* being pulled by KR and the already low tables. I thought that I must have had a bad tank of gas. I re-filled the tank with 91, but the problem persisted.

    After posting the problem on a truck board, members suggested that I enrich the mixture before boost (from 14.6:1 to ~13:1) to help keep cylinder temperatures down. I tried that with no luck. I am getting bad knock around 2000RPM at 80-100kPa 10* advance and 11.5:1 fueling on my wideband.

    I pulled the injectors and had them flow checked, they are within 1% of each other. I changed spark plug wires, and checked the spark plugs which all looked good. I checked my cats to make sure they hadn't melted, no signs of any trouble.

    I am probably running 15* less timing in most areas then I was previously. I cannot seem to tune out this problem, or find a mechanical problem. My dad spoke with Andy from A&A Corvettes this afternoon about what was happening. Andy said that his 2004 C5 had similar problems when he was trying to run in SD, he said that he has had cars that have had the timing wildly vary between cylinders from what is being commanded on #1 while in SD. Is there a possibility that my pcm will not function correctly with the MAF disabled? Should I load the stock OS back in then re-load the 2bar OS? Could it be possible that my pcm has errors, is there a way to diagnose them?

    Thank you again for the help,
    Henry

  8. #8
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    I fixed the out of range tables and went for a drive. Here are some logs, the knock is still unaffected by any changes I make.
    Attached Files Attached Files

  9. #9
    Lifetime Member 5.7ute's Avatar
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    Your VE table needs a lot of work. I would start the auto ve again from an unmolested table & get it right before touching the timing. If you are having troubles removing the transients have a search on this forum under filters & you will find some good info. I also have a spreadsheet for applying only a percentage of the BEN factor if you want it. It can help when there is a few transients you cant remove skewing the data.

  10. #10
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    Thank you for the help. I began the auto VE with a new VE and had much better success. I am within .5 of my commanded AFR now, with no spikes. I paid attention to the shape and continuity of the new table. I still have problems with detonation. I have reduced the timing by 20* from stock across the board, I still get audible knock at 2000rpm with 10* of timing at 80kPa. I will have more logs and a copy of the newer tun I am working with tomorrow. Thank you again for the help.

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