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Thread: Need help with driveability problem.

  1. #1
    Potential Tuner swoop's Avatar
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    Need help with driveability problem.

    Hey guys, having a problem with my car after transmission replacement. I broke the input shaft at the track, engine hit the rev limiter when it broke. The trans shop removed the front o2 sensors during repair. The rear o2's are deleted the are some sort of

    Now the car runs very poorly at cruise-light throttle after it warms up it gets worse. The air fuel ratio swings from very lean to very rich. Car runs great at wot. The only dtc it was showing said Maf performance error (immature) (pending)

    I'm not sure if my config file attached correctly, if not how do you get it into a format that will work? Thanks,Brian
    Attached Files Attached Files

  2. #2
    How big is the cam? Could be bent valves, I would do a compression test to verify its ok mechanically

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    Potential Tuner swoop's Avatar
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    Quote Originally Posted by joshmith View Post
    How big is the cam? Could be bent valves, I would do a compression test to verify its ok mechanically

    Cam is a 228/235 .614/.621 111+2

    I ran it at the track yesterday ( I know dumb) and it ran it's best times ever by about a tenth. I was thinking a possible valve problem too until it ran such a good #. I'll probably still do a comp test though. I'm disabled so I'll have to get some help to be able to check compression, I'll report back when I can get a buddy over to help.


    Would swapping left and right o2's cause something like this?
    thanks, Brian
    Last edited by swoop; 06-30-2014 at 06:09 PM.

  4. #4
    If the symptoms get worse after the car is warmed up, and the car still runs well at WOT, most likely something is wrong with the primary o2s. Sounds like it gets bad once it gets into closed loop.

    while it's cold it uses open loop, and at wot it uses open loop.

    Check the o2s are connected properly and that no wiring got pinched where the trans meets the engine. Also, in VCM scanner while driving try disabling and enabling closed loop and see how it changes the way the car drives to help isolate the problem as well.

  5. #5
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    Quote Originally Posted by xrelapse13 View Post
    If the symptoms get worse after the car is warmed up, and the car still runs well at WOT, most likely something is wrong with the primary o2s. Sounds like it gets bad once it gets into closed loop.

    while it's cold it uses open loop, and at wot it uses open loop.

    Check the o2s are connected properly and that no wiring got pinched where the trans meets the engine. Also, in VCM scanner while driving try disabling and enabling closed loop and see how it changes the way the car drives to help isolate the problem as well.
    Looking at your log, it looks like while cruising, (around the 6min mark and even before), your short-term trims are swinging violently, upwards of -60 and even hits -70+ in places. That seems excessive to me but I'm still new to this as well.

  6. #6
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    Quote Originally Posted by xrelapse13 View Post
    If the symptoms get worse after the car is warmed up, and the car still runs well at WOT, most likely something is wrong with the primary o2s. Sounds like it gets bad once it gets into closed loop.

    while it's cold it uses open loop, and at wot it uses open loop.

    Check the o2s are connected properly and that no wiring got pinched where the trans meets the engine. Also, in VCM scanner while driving try disabling and enabling closed loop and see how it changes the way the car drives to help isolate the problem as well.
    I tried new o2's and still same problem. Maybe even slightly worse. How do I disable closed loop? Sorry for the newb questions.

    thanks, Brian

  7. #7
    fuel>open/closed loop>closed loop enable, set the temp to 285...Hope its not mechanical, 235 degrees and 621 lift on the exhaust side is quite a bit. The exhaust valve is usually the one that gets it because the piston is "chasing" it. The piston is moving away from the intake valve. The old gm v6's would strip the teeth on the nylon cam gear and touch the valves, they would run pretty good cold but as soon they were up to temp they would miss bad. Bent valves are a vacuum leak, this is why under full throttle you thought it felt ok, a vacuum leak is a non factor when the throttle blade is wide open. I hope its something else and very well could be, I just wish you didn't bounce it off the limiter. How high is the limiter set?

  8. #8
    Potential Tuner swoop's Avatar
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    Looks like it was already disabled in the tune. Limiter is set at 6700 if i'm reading this right. looks like a compression check is in order. thanks for the help guys.

    Does the MAP reading look funny to you guys? We are thinking maybe the map got cracked when they tipped the engine back.
    Last edited by swoop; 07-03-2014 at 09:27 PM.

  9. #9
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    That MAP sensor log data definitely doesn't look normal.
    2001 Pontiac Trans Am M6 "cam only"
    228/232 110 cam, 10° overlap @.050" lift
    Edelbrock stepped headers, ORY, hooker catback

  10. #10
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    Quote Originally Posted by david_viny View Post
    That MAP sensor log data definitely doesn't look normal.
    Ok that's what I thought. Thanks

  11. #11
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    MAP is flatlined at 85 Kpa most of the time. That's where your issue lies. I would check the wiring to it. Make sure it's fully plugged in. Make sure the sensor and/or wiring was not damaged during the trans swap.

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  12. #12
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    Quote Originally Posted by edcmat-l1 View Post
    MAP is flatlined at 85 Kpa most of the time. That's where your issue lies. I would check the wiring to it. Make sure it's fully plugged in. Make sure the sensor and/or wiring was not damaged during the trans swap.
    Ok cool, thanks a bunch. Have a friend going to help me tomorrow so hopefully we can get this thing fixed.

  13. #13
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    Looks like a vacuum cap got ripped during the trans replacement. Pulled the intake today and found it, car runs great again. Thanks again for the help guys.