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Thread: Diagnosing Low Power, Low Idle Problem

  1. #1
    Garrett booster
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    Diagnosing Low Power, Low Idle Problem

    Hey y'all. My 1989 Dodge Spirit is running pretty poorly (a413, stock tune, Garrett T2, intercooler). It idles below 500rpm when warmed up. And she just seems...super slow...like TBI slow.

    I went through the minimopar trouble shooting guide and checked the TPS, replaced the speed sensor (but the speedo is still dancing), and replaced the AIS. I did try to reset the AIS, but it never jumped to 3000rpm when I introduced a large vacuum leak

    from minimopar
    If you do not have a scan tool, you can use this method (special thanks to Steve Calder for the vacuum leak idea):
    1. Induce a large vacuum leak by disconnecting the brake booster line. This will cause the engine speed to increase greatly (around 3000 RPM or more).
    2. The engine speed will drop as the computer tries to compensate by closing the AIS valve.
    3. When the engine speed stops going down (give it a minute or so), disconnect the connector on the AIS motor. With luck, the AIS valve is now closed. This will also set a fault code 25.
    4. Reconnect the brake booster vacuum line (the engine may stall, so open the throttle a bit).


    And these are the codes I was dealing with:
    12 caused by disconnecting my battery. I'm sure it'll go away
    24 (TPS) - checked TPS with MPScan...totally fine
    45 (turbo boost limit exceeded) - I did this setting the up the boost controller...should I still be worried?
    52 (bad O2 sensor) - replaced the O2 sensor
    55 - end of codes


    Is there something that I'm missing that would trigger all of these codes but be ONE problem?

  2. #2
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Diagnosing Low Power, Low Idle Problem

    I would check the cam timing, then I would do a compression test if the cam timing was spot on.

  3. #3
    Garrett booster
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    Re: Diagnosing Low Power, Low Idle Problem

    Distributor timing was off! I’m not sure how that happened. But I took everything apart and lined up the distributed key parallel to the block. I warmed up the car and set the timing at 12/14ish. I also figured out that my Cal was messed up. The default engine temp was set super low.

    Running good now! Btw, I used your YouTube video, Cordes. Thanks!


    I did end up testing the compression. 120psi all around :-)

  4. #4
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Diagnosing Low Power, Low Idle Problem

    Great to hear. Glad that it was relatively easy and that my video was of some help. It's always nice when something doesn't take money to fix.

  5. #5
    Garrett booster
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    Re: Diagnosing Low Power, Low Idle Problem

    Quote Originally Posted by cordes View Post
    Great to hear. Glad that it was relatively easy and that my video was of some help. It's always nice when something doesn't take money to fix.
    you scared me when you mentioned compression lol.

    Is there any advantage to advancing the cam one click? I came across this old Allpar article that recommended advancing 1 tooth for more low end torque…but I haven’t really seen that recommended here on this forum.
    Last edited by Fenderbass; 07-30-2021 at 09:14 PM.

  6. #6
    Supporting Member Turbo Mopar Contributor GLHS60's Avatar
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    Re: Diagnosing Low Power, Low Idle Problem

    Changing cam tuning by 1 tooth can change things but it's not beneficial.

    Advancing helps low end but you run out of steam around 3500 RPM.

    Retarding kills bottom end but can improve the top end.

    Still, 1 tooth is too much the vast majority of the time.

    Thanks
    Randy


    There is no logical reason to call an Engine a motor.

    Randy Hicks
    86 GLHS60
    86 GLHS 373 : SOLD, but never forgotten
    89 Turbo Minivan
    83 Turbo Rampage : SOLD
    Edmonton,Alberta,Canada

  7. #7
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Diagnosing Low Power, Low Idle Problem

    Quote Originally Posted by GLHS60 View Post
    Changing cam tuning by 1 tooth can change things but it's not beneficial.

    Advancing helps low end but you run out of steam around 3500 RPM.

    Retarding kills bottom end but can improve the top end.

    Still, 1 tooth is too much the vast majority of the time.

    Thanks
    Randy
    Randy nailed it. I believe that one tooth on the cam gear is about 9*. That's way too much. If you had an adjustable cam gear, you could play around with the settings to see what got you the best gains.

  8. #8
    Garrett booster
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    Re: Diagnosing Low Power, Low Idle Problem

    Thanks guys. I’ll keep the timing where it should be :-)

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