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Thread: 01 Monte no codes 3800 N/A RPM limit at 3700?

  1. #1
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    01 Monte no codes 3800 N/A RPM limit at 3700?

    I've been trying to troubleshoot a friends 01 Monte Carlo with the 3800 N/A motor. I'm not new to HP Tuners but am new to this platform.

    The issue:
    At 50%+ throttle, won't rev past 4K and starts bucking wildly around 3700 RPM. From the scan logs, the computer looks to be pulling fuel (maybe cutting out cylinders) on purpose. Happens in all gears.

    What I've changed:
    Removed a ton of timing to fix the KR
    Ensured computer is seeing the gear selector so it does not think it is stuck in park/neutral
    Reset the rev limiters for P/N to 7K just incase
    Turned off all engine and trans torque management
    Checked for trouble codes

    Previously owner changed:
    O2 sensors
    CAT

    Attached the last tune, scan logs and configs
    In the scan log you will see the injector pulse width start dropping off at 3700 at WOT. If he backs off on the throttle to say 40ish %, it will rev out without issue. Symptoms match if trans/torque management/abuse mode was being triggered but that is now all turned off in the tune.

    At this point, I've run out of things to try. Any suggestions of additional PIDs to watch with the config?
    Attached Files Attached Files

  2. #2
    Tuning Addict 5FDP's Avatar
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    First off, I havent seen this problem yet with a 3800, so I am not sure what to say on that part.


    But I will say, its a really really bad idea to remove tons of timing from the spark tables, these NA cars knock when stock, you can't get around it. Its very common to see anywhere from 5-8ยบ of KR stock, taking away lots of timing to make that go away is not the correct way to fix the problem.

    The motor needs exhaust flow and 91+ octane fuel to better help it. The cast front manifold and the wimpy 2 1/4in downpipe with the u-bend make for a poor flowing exhaust. But thats another topic.

    I've also noticed that removing all of the TQ mgnt is not a good idea either, its okay to take away some but you still want some there.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
    Tuning Addict 5FDP's Avatar
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    Also the SES doesnt flash on and off quick does it?
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

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    Took the timing out just for testing. At first it appeared the computer was pulling timing and fuel but it's just fuel. SES light does not flash, tried same test with and without traction control on.

    When in open loop (before it fully warms up), WOT pulls right through to 6K.

    Good to know about the stock KR. When I get past this issue and do a real tune for him I'll keep that in mind.

  5. #5
    Advanced Tuner Dr. Nopps's Avatar
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    Sorry to just butt in here, but... The GM V6's running N/A are very sensitive to any AFR much richer (edit) than 13-1, once warmed up & at normal operating temperature. Their factory set O/L Fueling Tables are set up to dip richer than that, and Acceleration Enrichment is initially set to be allowed while at WOT, adding even more fuel than PE was set to. This horrible combination was usually good for at least 4-6 degrees of KR on a limited, casual, highway speed burst. I don't allow Acceleration Enrichment at WOT, and limited the most extreme areas of my O/L Fueling table never to go richer than 13-1. It was like a magic wand. No knock, even with 87 octane. Substantially more timing could even be used with 93 octane or higher rated fuel. I'll post my tune below. Check out the calibration details icon to see why I did everything in there.
    01 Malibu A-T 3.1L 93Rev..hpt
    Last edited by Dr. Nopps; 08-06-2013 at 10:49 AM. Reason: Writers error

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    QQ: Dr. Nopps, you said sensitive to any AFR much leaner than 13-1...you meant much richer right?

    Good info, I'll keep that in my back pocket once this bucking issue is resolved. Compared with the current tune and found a spot where I did not turn off the torque management correctly. I don't think it will make a difference with the current issue though.

  7. #7
    Advanced Tuner Dr. Nopps's Avatar
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    Yes. I apologize and thank you for catching that! I'm usually pretty good at proofing my text before posting, but I got caught slippin yesterday. LOL. I'll Edit.

  8. #8
    Advanced Tuner Dr. Nopps's Avatar
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    Might as well actually try to help too while I'm here right? Not too many mods, making things a "little" easier. Go back to the original factory tune for a couple of runs/scans. If it still has drivability issues, leave that stock tune in there and figure out what isn't mechanically sound with the engine. Could be anything from a bad sensor, to a bad injector, bad gasket somewhere, or even improper fitment of a part from the previous owner - potentially causing a leak, or damage from the wrong part, or hopefully someone just forgot to plug some harness or connector back in. Either way, start from the stock tune and fix the car from there, then put those credits you purchased and committed to good use. Your friend should actually be very pleased, if not downright impressed with the results, (of a nicely tuned 3800) once this is all ironed out.

  9. #9
    Senior Tuner Russ K's Avatar
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    You need to log Maf Hz. Looking at you log, the Maf g/sec is erratic by 3800 rpm and the O2 drops lean. I've had bad Mafs cause this before.

    Russ Kemp