350 Mag MPI question on 555 relay fuse blowing.

[c1steve]

A year ago I pulled the IAC cable off while the engine was idling. An hour later a 20 amp fuse blew. This fuse powers the fuel injectors and coil. Twice since then the same fuse blew, and today it blew twice more while out in the ocean.

It tends to blow just after increasing RPMs to cruise (3,500 typically). I have replaced the 50 amp breaker, plus the main power relays and the fuel pump relay. 6 years ago I replaced the coil, and believe I used a Mallory RA117011. I am not sure if Mallory parts are good, or as bad as Sierra. I have read that some Merc coils died early, and that an issue with the tach can also cause problems.

Any suggestions?
Also, is there a more cost effective coil than the Merc. that is cost effective? Sierra quality has been terrible, I do not trust them. Merc coil: 8M0054588

 

[alldodge]

Its hardly ever the coil, they just don't fail. I think the ECM has a driver inside it that is drawing more current

If you have to throw a coil at it it's made by AC Delco. Search for AC Delco 8M0054588 coil, and can find some on ebay much cheaper

I would suggest contacting John at boats unlimited and see what he can do
https://www.boatunlimited.com/

 

[c1steve]

Thanks for the recommendation. I have the old coil, there was nothing wrong with it. This weekend I will do some testing with my ammeter, and swap some parts. Will try to determine what is causing the circuit overload.

 

[c1steve]

Thought I would give an update on what caused the problems on my engine.
Primarily the newish coil had some sharp edges on the aluminum portion of the bracket. This abraded the wiring harness that was just above it, eventually shorting the wire the was connected to the 20 amp fuse.

Second the house battery was tired, and when picking up the crab pot we had just dropped, the 6 amp output of the kicker motor was insufficient to power the pot puller. The battery voltage went way down, causing the electronics to shut down.

Everything is working fine now, hope albacore tuna come close enough to get them in my small boat.