454 ignition issues

1989 454 crusaders, starboard engine keeps eating ignition modules. Prestolite distrib. in place with donut style module, have also replaced with a new Petronics distrib. with same results. Can only run about 10-20hrs before engine will start to "pop". When this occurs I need to replace module. Don't know if voltage spike is issue, I have added 12 volt relay to get "clean" power right from battery to coil and still happens.
Port engine only happened once over 1yr ago. Ideas on what I'm missing ?

I had my first prestolite module failure after over 20 years, just last year. The other one i replaced only because of the pot metal external corrosion. I can only think that you are running coils that want an external resistor, and one is not present.

Dave, I am using internal resisitor coils (MSD). Just talk with local marine mechanic and said it could be problem with tach shorting on neg. side (gray wire on coil) removed ot and running today to see the Blue Angels show. Will see if any difference.

Also the Prestolite module papers state to remove any external resistor

At least $70 a pop, hope you find resolution fast. Plus, they will stop the engine without warning. I do recall that verbage about the ext resistor with my paperwork; i'm using a jacobs omnipac, btw.

the tach shorting theory would stop the engine from running but shouldn't have an impact on the module. I think Dave's thought is spot on but I'll tweak it a bit. I'm thinking the MSD coil's internal resistor lets a bit more current run thru the primary than the prestolite trigger module wants to switch. I haven't played with MSD's since the "-7" ignitions came out and they make that hot spark by using a lot of energy. Being as the supply voltage is fixed at 12 VDC, they only way to get the "extra" energy is to consume a few more amps. just something to consider.

Update, went to see Blue Angels at Severn. Great show as always. Still had starboard engine issues. First would not run up past 2500rpm without popping (thru carb). I believe this is a lean issue? Possible clog in secondary circuit? After sitting at anchor for 3+ hours engine stalled and would not restart. Limped home on port engine, will try to remove and tear down carb for rebuild ( Q-Jet). Mark what coil would you recommend for the prestolite ? Tach disable had no bearing on operation.

FA-18: i recall diving for my 2 year olds ears to cover them. Was at the shell air/sea out of ft. lauderdale 6 years ago. The pilot was doing a 6 g hi-po turn DIRECTLY overhead of our boat at about 150 AGL. Fabulous. mach rings in the daytime...

Luhrs - I'd start with a stock one.

DD - I think I've got a couple jpegs with the mach rings, taken pretty much co-altitude. If interested, I can email them.