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Thread: MPscan issue or bad VSS?

  1. #1
    Mitsu booster
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    MPscan issue or bad VSS?

    I got a SCI cable and MPscan setup and everything working (I think) but hadn't done any data logging until a couple days later when my car (87 Shelby Lancer) started idling extremely lean and miss firing, if moving and it builds boost it richens up and stops miss firing. Its not throwing any codes but the VSPD gauge in MPscan always shows 0 MPH and the AFR is stuck at 8.0:1 even though my wide band is reading correctly. Should I blame the VSS? Or is there something in MPscan I'm missing and I should continue looking for whats causing the extremely lean issue?


  2. #2
    Supporting Member Turbo Mopar Contributor
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    Re: MPscan issue or bad VSS?

    if this is an LM ecu then i don't think the wideband interface has been set up. send me your config file (ends with .mpc). i'll look at it. how did you get the AFR gauge on there? are you using the most current version of mpscan?
    89 Voyager LE, 2.5T2 - rest in peace
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  3. #3
    Slugmobile & MeanMini Caretaker Turbo Mopar Contributor wheming's Avatar
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    Re: MPscan issue or bad VSS?

    MPScan is a datalogging program with some other features, but it does not change any ecu programming. It is just a passive monitor.
    So, the hardware (engine, wiring, sensors, etc) issues you have first need to be resolved before you can troubleshoot MPScan unfortunately.

    Also you are on a logic module?
    I don't know if the WB2NB function works for LM cars. Morris or someone else would have to chime in on that.
    The AFR gauge that was in MPScan was a calculated gauge that I don't think ever worked accurately. The AFRwb gauge needs the WB2NB function, and you 0-5v wb output. There are more threads about that also.

    The VSS gauge should have some change while driving obviously. Does your speedo work? Do you have a speedometer cable or just a speed-distance sensor on your trans tailhousing?

    Your lean idle and misfiring is some issue you need to troubleshoot. Could be alot of things. Start with basics first, then see if it helps. Basic tune up items, fuel filter, verify fuel pressure, check HEP, and ignition/spark.

    It is best to only try setting up the mpscan gauges after your car is running well, so you can tell if the readings and setup of mpscan is correct.
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  4. #4
    Mitsu booster
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    Re: MPscan issue or bad VSS?

    Thanks for the replys!

    I should rephrase my question. Would a bad VSS cause a steady extreme lean condition, over 18:1 AFR, at idle?

    Quote Originally Posted by wowzer View Post
    if this is an LM ecu then i don't think the wideband interface has been set up. send me your config file (ends with .mpc). i'll look at it. how did you get the AFR gauge on there? are you using the most current version of mpscan?
    Yes. It's an 87 LM. AFR was one of the gauge options. I didn't have my thinking cap on and was thinking it would go off the narrow band haha. But at the time I was setting up gauges I was just playing, trying different things. It is the newest version.

    Quote Originally Posted by wheming View Post
    The VSS gauge should have some change while driving obviously. Does your speedo work? Do you have a speedometer cable or just a speed-distance sensor on your trans tailhousing?

    Your lean idle and misfiring is some issue you need to troubleshoot. Could be alot of things. Start with basics first, then see if it helps. Basic tune up items, fuel filter, verify fuel pressure, check HEP, and ignition/spark.

    It is best to only try setting up the mpscan gauges after your car is running well, so you can tell if the readings and setup of mpscan is correct.
    The speedometer works and has a cable along with the speed sensor. The speedometer in Mpscan did not move at all during a 15 minute log/drive I did. The car was running well and it was just a conincidence the cable arrived a few days before it started running poorly.

    Fuel pressure is good. I had thought about the fuel filter and will verify it's not getting plugged but I had assumed it would want to run leaner under boost and/or load if it was a fuel filter issue.

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