OMC 4.3 occasionally, mysteriously dies, then starts fine. Electrical issue.

[took-the-red-pill]

Hi there,

-1988 OMC Cobra. Runs like a top. However, it just randomly dies every 5-10 min. when we're out boating.
-Then it starts immediately with no issues or hesitation.
-The reason we know it's electrical is that we ran it out on the lake with the engine cover and a multi meter hooked up to it.
-It would run fine, at various RPM's, doing various maneuvors.
-The multi meter would read 8 volts, which is what it runs at.
-Suddenly the multi meter goes instantly to zero volts and it dies, as if the key were shut off.
-We don't have to be moving the shifter at all for it to happen. So it's not like we wiggle something and it shuts down.
-It's truly random.
-We went through the wiring many times -with my car-guy buddy - and everything we tested is fine.
-Everything tests out with the multi-meter - wires, switches, coil, key assembly, everything.
-Sorry, but it was last year, so I can't remember exactly which wires we had the multi meter across when we saw it go to zero volts.
-We tried bypassing each wire individually, in case one of them was broken inside and cutting out. it still died.
- I changed coil, the main coil feed wire between it and the distro, and ignition. It still dies.

In frustration I bought a resistor and basically hot wired it, so we were starting it on full 12 V, and then flipping the switch down to 8 volts to run. It has never died once when in hot wired mode.

Any ideas?

1. Should I start with the ESA/overstroke switches? (I didn't think they would send it to zero volts).
I've played with the shifter in my parking lot and the W thing appears to be operating correctly by clicking the switch when I move the shifter.

2. The friend helping me said it is probably a sign that the alternator is going. I don't think so.
The alternator is charging just fine. It kicks out 14 volts, without fail. The battery is good and holding charge, and starts the boat every time, and has done so for a whole season since this issue started.

 

[kpg7121]

I had a similiar issue on my Cobra a few years ago. I replaced the ignition switch & that took care of it.

 

[Lou C]

Your clue is....when you hotwired it...which wiring in which circuit did you by pass? Keep in mind that the ignition circuit is fed by the fusebox and the ignition switch. If that wiring is loose, or corroded, the engine will just die like that. I had a no crank, no gauge issue a few years ago. Drove me nuts for a while then I thought of checking the fuse...well....it had continuity...so not blown...but...took it out (old style glass fuse with the metal ends, with metal clips in the fuse box to hold it in). The problem turned out to be oxidation that prevented current from flowing, through the fuse. I replaced all those fuses and no more problems since.

ever try wiggling the ignition key or reaching up behind the dashboard and wiggle the switch slightly when its running (not in water on land lol)...does it die then? The old style ignition switches are easy to change, there is a B terminal (battery, red wire), an I terminal (Ignition, purple wire) and S terminal (Start, red/yellow wire). My guess is the one affected is the purple wire if the engine dies but the tilt n trim still works. So it could be oxidized fuses, bad connections at the fuse box or ignition switch, or the switch itself.

 

[took-the-red-pill]

I changed ignition and fuses early on in this process. No effect. Still dies.

 

[kenny nunez]

One other place to look at is the main cannon plug where it connects to the engine. Pull the plug and with a thin screwdriver gently spread each pin and add some dielectric grease. Also a wire that has all but 1 strand not cut will show a good circuit but not able to carry a load . Take a close look at the wire harness from the instrument panel for any damage. A good example would be a hole drilled through it or a screw penetrating from the rub rail.

 

[CaptCrunch205]

There are 2 larger fuses in a rubber harness on the back side of the engine as well. Check those and make sure they are not corroded. I had one that the glass was cracked and it gave me fits. Had no idea they were there. Carry 2 extras in the boat now.

 

[Lou C]

Yep on the cannon plug, they come with a spring clamp on them but I took it apart, and greased the terminals and also put di-electric grease on the rubber housing (so it would slide all the way together) and then put a hose clamp over it. That way it will not loosen. Take a good look at the engine wiring harness, trace it from the battery to the ignition coil.

 

[took-the-red-pill]

I guess I can give these things a shot. It’s starting to look like a One Stick Problem - in my family we rate problems by the number of sticks of dynamite it would take to make the problem go away.

 

[took-the-red-pill]

SOLVED! A buddy of mine said that since I had essentially changed everything else on the boat, that in his 30+ years of playing with cars it was the alternator. It had not completely crapped out but it was, in his opinion, dying a slow painful death.. I didn't see how that was possible, but he said to try it.

I replaced the alternator and the boat runs like a Swiss watch. It has never stalled since. It used to mysteriously die 5-6 times per hour, and this year I've put maybe 60 hours on the boat with nary a hiccup.

I'm posting this to hopefully help others with the same or similar issue.