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Thread: Need help with engine miss.

  1. #1
    Tuner in Training
    Join Date
    Dec 2013
    Posts
    14

    Need help with engine miss.

    I'll preface again that I am brand new to HP tuners so I may be asking the wrong/or stupid questions.

    This a 04 5.3L engine in a kit car that I built (Factory Five Daytona Coupe). It is controlled with a 02 F-body computer and stand alone harness. It is mostly a track car, but it gets driven on the street as well. It was initially tuned by an experienced tuner but has developed a under load high rpm stutter. It is really bad when you first start driving (but after ECT is above 180F) and is mostly gone after 10-20 mins of driving. So basicly I start the car and drive for a bit to get the engine temp up to normal, and then do a third gear WOT put. It Pulls good to about 4K rpm and then is stutters and misses so bad that it will barely rev past that point. I then drive for about 20 mins (or on the track it takes about two laps) and then do a pull again and for the most part will rev right to 6500 rpm without stuttering too much. It still does, but not nearly as bad. In all other driving relms it runs great wether it is warm or cold.

    My first thought was some sensor on the engine needed to get heat soaked before it started working properly, and I thought it was an ignition thing. But now looking at the data logs it appears to be a fuel problem.

    coldpull1: logging mostly sensor data and misfire data. Pull starts at frame 383.
    coldpull1.hpl

    coldpull2: logging the default data (I forgot to log my WBo2), pull starts at frame 128.
    coldpull2.hpl

    hotpull1:logging same as coldpull1. pull starts at frame 489
    hotpull1.hpl

    hotpull2: logging same as coldpull2. Pull starts at frame 126. I also did some steady state logging at the end of this log.
    hotpull2.hpl

    The thing that jumps out the most to me is the difference in the injector duty cycle and injector pulse width between coldpull2 and hotpull2. It is very eratic in the coldpull one compared to the hotpull one. What could be causing this?

    See next post for config and tune files.

    Thanks for any help
    JC
    Attached Files Attached Files
    Last edited by jkrueger; 01-11-2014 at 09:05 PM.

  2. #2
    Tuner in Training
    Join Date
    Dec 2013
    Posts
    14
    Here is the config file for coldpull1 and hotpull1.
    JCsensor testing1.cfg

    Here is the config file for coldpull2 and hotpull2.
    Default Imperial.cfg

    And here is the tune file.
    first changes2.hpt

    JC

  3. #3
    Tuner in Training
    Join Date
    Dec 2013
    Posts
    14
    From the research I've done it looks like the MAF and RPM is the only sensor the PCM uses to determine fuel (injector PW) during WOT. I posted the pictures below for easier viewing. The first one (coldpull2) is after a few minutes of driving after the engine warmed up. Pretty erractic MAF signal (is this normal?) and the a very erractic injector duty cycle and PW. This is what I think is causing my stuttering, even though the WBO2 doesn't show it (must not have a fast enough resolution) I think it is lean. The second picture (hotpull2) is after 20 mins of driving and the engine heat soaked now). Much better acceleration and only a little bit of stuttering.

    Think maybe I have a bad MAF?

    Coldpull2.jpghotpull2.jpg