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Old 02-06-2023, 08:41 AM
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Default 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.

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Old 02-06-2023, 10:48 AM
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What happens to the A/F and fuel pressure when this occurs? Does your fuel regulator have a boost reference line? Do you have the proper MAP sensor? Plug gap?
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Old 02-06-2023, 02:32 PM
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To be honest I do not know what happens to either of those, as I don't have a guage for them. Something I will be working on. This system has been working for the last 10-12 yeas and recently started to give me heartburn. The spark plugs are gapped to .030".
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Old 02-06-2023, 04:05 PM
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Quote:
Originally Posted by mdprovee View Post
To be honest I do not know what happens to either of those, as I don't have a guage for them. Something I will be working on. This system has been working for the last 10-12 yeas and recently started to give me heartburn. The spark plugs are gapped to .030".
You should be able to see if it's going lean or rich by datalogging it. I would start with that.
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Dakota Digital for their Chevelle HDX Gauge Package
Painless Performance for their wiring harness

Ron Davis Radiators for their radiator and fan assembly.
Baer Brakes for their front and rear brakes

Texas Speed and Performance for their 427 LS Stroker
American Powertrain for their ProFit Magnum T56 kit
Currie Enterprises for their 9" Third Member
Forgeline for their GF3 Wheels
McLeod Racing for their RXT street twin clutch
Ididit for their steering column
Holley for their EFI and engine parts
Lokar and Clayton Machine for their pedals and door and window handles
Morris Classic Concepts for their 3 point belts and side mirrors
Thermotec for their heat sleeve and sound deadening products
Restomod Air for their Tru Mod A/C kit
Mightymouse Solutions for their catch can
Magnaflow for their 3" exhaust system
Aeromotive for their dual Phantom fuel system
Vintage Air for their new Mid Mount LS front drive
Hydratech Braking for their hydroboost system
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Old 02-07-2023, 05:20 PM
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A friend used RPM (https://www.rpmeng.com/dyno-tuning-rohnert-park) in Rohnert Park a couple years back for TBI/EFI tuning help. Had good feedback and not too far of a drive from Suisun City.
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Old 02-08-2023, 08:40 AM
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Thanks, going to try and see if I can get some datalogging done this weekend, and will check on RPM.
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Old 02-19-2023, 04:41 PM
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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.
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Old 02-19-2023, 10:25 PM
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personally I would throw the MSD box in the trash. Every car I have ever used one on would eventually have issues. I would tighten your plug gap another .005.
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Old 06-09-2023, 09:07 PM
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Quote:
Originally Posted by ADY View Post
A friend used RPM (https://www.rpmeng.com/dyno-tuning-rohnert-park) in Rohnert Park a couple years back for TBI/EFI tuning help. Had good feedback and not too far of a drive from Suisun City.
Its been a while and life got in the way of fixing the car. Took it to RPM 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.

Thanks for the referral.
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Old 06-10-2023, 05:47 PM
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Wow. What would cause all of that rust?
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