Results 1 to 8 of 8
Thread: MIssfire under Boost
-
02-06-2023 #1
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
-
02-07-2023 #2Registered User- 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.
02-08-2023 #3Thanks, I will look into those.
My plug gap is at.030"right now.Mike
02-19-2023 #4I 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.
Mike
02-20-2023 #5Registered User- 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.
06-09-2023 #6Its 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.Mike
06-14-2023 #7