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

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?

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.

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.

Thanks, going to try and see if I can get some datalogging done this weekend, and will check on RPM.

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.

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.

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.

Wow. What would cause all of that rust?

I've seen rust like that on MSD's even in Sacramento which is low humidity.

Yeah mine did that too.... think it's just condensation from the heat. I found it when I went to EFI and replaced it with the hyperspark set up. My car was running fine before that, I just found it when I did the swap.
Back in the day I remember guys talking about drilling a small hole in the cap to let out the moisture that would tend to build inside the cap

MSD stuff is made for weekend warriors in performance applications. Their caps wear quickly too. OK for low mileage applications. Not so much for a daily driver or longevity. JMO

MSD 6 BTM
 

Glad you got it back up and running!

Food for thought:

When I had a Paxton Novi on my Fox body Mustang years ago I ran a MSD BTM so that it would back off timing as boost increased. I was spinning it up to 10-12lbs of boost with that set up without issue...

Another thing you could look into is a dual sync distributor so that your ECU is controlling the timing and the air/fuel ratio.

Yea not sure why it rusted either. Something I will keep on eye on now.

Thanks I will look into the MSD 6 BTM.