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    Results 1 to 8 of 8
    1. #1
      Join Date
      Aug 2004
      Location
      Suisun City, Ca.
      Posts
      792

      MIssfire under Boost

      Hello and hope you can help. I have a 383 SBC with Fast XFI 1.0, Holley Stealth Ram, and P-1SC Procharger. I have a MSD 6AL box and MSD Coil. I dont know alot, and have been chasing a problem. It just started within the last year. It runs great from idle to when boost starts. Once the boost kicks in (about at 4-5 PSI), the motor starts to misfire and cut out. I have replaced the cap and rotor, plug wire and gone thru several sets of plugs. Any ideas I can check? Thanks for your help.

      Mike

      ________

      Mike


    2. #2
      Join Date
      Mar 2020
      Posts
      195
      I'll mention a few items that you likely have tried, but...

      1. Have you experimented with the plug gap (reducing it sometimes helps) & what gap are you running?
      2. Do you have an in-car fuel pressure gauge to verify the pressure is stable under boost?
      3. What is your air/fuel ratio?
      4. Have you tried to remove the blower belt & remove the intake piping to see if there is a problem at WOT & no boost?

      Another item to consider is under boost, the pressure acts against your intake valves offsetting your valve spring pressure.
      If you lost some spring pressure over time it can be an issue that causes valve float.

    3. #3
      Join Date
      Aug 2004
      Location
      Suisun City, Ca.
      Posts
      792
      Thanks, I will look into those.

      My plug gap is at.030"right now.
      Mike

    4. #4
      Join Date
      Aug 2004
      Location
      Suisun City, Ca.
      Posts
      792
      I took the car out today and removed the blower intake tube so the motor saw no boost. No cut out till the motor hit the rev limiter at 5500RPM. Then we connected the intake tube back up and ran it. The RPMs are around 4500 to 5000 RPM when it cuts out and around 7 lbs boost according to the guages. Here are the data logs. My plugs at set at .025 gap. Please keep in mind it is a manual car, so the big dips are me shifting.Name:  LOG 1.png
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      Mike

    5. #5
      Join Date
      Mar 2022
      Posts
      120
      Are you running out of duty cycle on your injectors? It happened to me when I would turn up the boost on an old car I had. I switched to bigger injectors and the problem went away.

    6. #6
      Join Date
      Aug 2004
      Location
      Suisun City, Ca.
      Posts
      792
      Its been a while and life got in the way of fixing the car. Took it to RPM in Rohnert Park and they were amazing. Made a appointment and they got the car right in. It was a rusty distributor. After replacing the distributor, they did a little tuning and it is running great. 475 horsepower to the wheels.


      I would definitely refer them.
      Attached Images Attached Images      
      Mike

    7. #7
      Join Date
      Sep 2006
      Posts
      273
      Country Flag: United States
      wow. good catch.

      I had my MSD crap out on the magnetic pickup. it would get warm and shut the car off. after several boxes and coil swaps..... it ended up being a $20 part. so frustrating. Pretty wild how these parts can fail and still look new on the outside.

    8. #8
      Join Date
      Dec 2011
      Posts
      41
      Country Flag: United States
      that is pretty rusty lol





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