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Thread: HP shutting down with boost increase.

  1. #1

    Default HP shutting down with boost increase.

    Changed pulley size on Vortech YSi to increase boost, now shutting down due to rich condition. A/F Ratio going down to 9.9. Believe this is way over rich. As the boost increases it seems like somebody just shuts the key off. This problem started after pulley change to increase boost. Running at 8 psi never had an issue. Now at anywhere from 11 to 13.9 psi, I get this shutdown. No popping shutter or anything. After the issue car just goes about its merry way, with reduced throttle that is.

    Originally thought the Learn Table had never been in the higher boost areas, but subsequent tests show overly rich condition exists. Have learning enabled with Closed Loop. Most of the time this occurs with an accompanying rich condition, but even unburnt fuel will cause a rich A/F Ratio. I'm starting to think there's more to the picture than the tune.

    I'm running a MSD Digital 7 CDI box with MSD HVC II Coil (big red one) with MSD 351 Ford distributor. Going to rebuild Automotive regulator, but starting to think this is not the problem. Would appreciate another pair of eyes to see that there's nothing I'm doing wrong.
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  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    27,458

    Default

    Spark plug gap?

  3. #3

    Default

    Go back to 8 psi boost to see if the car runs fine there. Sometimes a problem happens at the same time a change is made and it's easy to confuse cause & effect. If you have the problem at 8 psi then something else has happened. If you can verify that it is boost related, then it's easier to solve.

  4. #4
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
    1,741

    Default

    Your boost drops out slightly before the RPM drops. Find out why it's losing boost.

  5. #5

    Default

    Quote Originally Posted by Danny Cabral View Post
    Spark plug gap?
    Worth a shot.Thanks Danny.

    Quote Originally Posted by AndyF View Post
    Go back to 8 psi boost to see if the car runs fine there.
    Makes sense, another problem could have popped up.

    Quote Originally Posted by 81 TransAm View Post
    Your boost drops out slightly before the RPM drops. Find out why it's losing boost.
    Going to take a closer look. Thanks for looking.

  6. #6

    Default

    I see that's a 10th of a second later, but I'll look into it further. Of course the AFR ratio is shot at that point, at 9.8. Thanks for the response and looking.
    Last edited by jdefina; 10-15-2020 at 09:43 AM.

  7. #7

    Default

    Well Danny, you might have hit it. I pulled driver side today and replaced plugs...tomorrow the other. Gaps on the plugs removed were .036"-.038". New set going in at .025".
    Still a little skeptical. MSD Digital 7 with large HVC coil not able to fire at 11-12 lbs of boost. Will find out after testing.

  8. #8

    Default

    Could be that simple. The ignition could fire the wide gap at 8 psi but not at 11 or 12 psi. Just try it & see. That's a cheap fix if it works.

  9. #9

    Default

    Did the other bank today, gaps were pretty much the same on that side. Probably give it a test tomorrow, I'll post results.
    As I posted on Danny's reply, I'm still a little skeptical. It might fix the problem, but I'd think 11-12 psi of boost even at .038", a of Digital 7 ignition and HVC coil should be capable of that.
    Which make me think there might be more to this than the gap. But I certainly I'm not any engineer, so we will find out. Thanks for taking the time to look!

  10. #10

    Default

    Well took out for test after plug change and gap at .025" with no luck.

    Seems to be getting worse, now only at 4800 RPM with 7.5 lbs of boost. Again no misfire up to that point or after just nose dives.
    The last test, I slow pedaled it and still occurred. I'm starting to think something is failing in the ignition chain.

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