Intermittent Engine Problem
 

I was out on my boat yesterday and encountered an intermittent engine problem that I would like some advice on.

At idle or cruise speeds ,the engine will cut out occasionally and then continue running like normal. It's almost like you shut off the ignition switch for 1 second and then turned it back on. I don't believe it is a fuel issue, but I could be wrong.

The alarm will also sound for a few seconds then back to normal. Drive lube is full, Engine temperature normal, oil pressure normal.

Engine is a 523 cu. in custom build with a Mefi 3 computer with a modified tune. Originally it was a 502 MPI.

I doubt scanning it will work as the computer was changed from factory settings by the engine builder, and when scanned for a previous problem the tech couldn't get a good reading? Also there are no decent tech's near me .

I was thinking it could possibly be the lanyard switch or possibly the ignition switch, but not sure how to test with an intermittent problem.

Any advice or suggestions on where you would be looking would be appreciated.

How comfortable are you with electrical work ? You could try wiggling the lanyard and the ignition switch while it is idling and see if either of them does anything but to go any further you probably need an ohm meter to start checking switches and connections. You could also shut off the batteries and just go through and tighten any electrical connection you can find. Unplug any connectors and look at the pins for corrosion and then plug them back together. Those are the things I would start with.

How long has it been since the engine was out and everything was disconnected ?

Sounds like a short somewhere for sure. Intermittent stuff is the hardest to find. I had an issue for a few years that only happened maybe 0 - 2 times a year. Once in while I would hit a couple normal 2-3' waves and starboard engine would stall you like turned off the key. Jiggle some wires on the engine and it would restart and be fine for days, weeks, months and all of a sudden would do it again. Finally found the purple (ignition key on power) in the alternator harness had just barely rubbed through and was hitting an engine mount and grounding out.

Might check the round 9 pin engine harness plug, might have worked loose

I removed the ignition switch and lanyard switch and they seem to test good. It will probably be better to reinstall them and check with engine running and try moving everything around. I also cleaned the cannon plug with some electrical cleaner.

Going to start digging around and cleaning and checking as many connections as I can find..

Would the fact that the alarm sounds for a second or two and then silences lead to any particular area I should be looking at.?

Low/no oil psi (sender for ecu is multi wire vs 1 wire for gauge) which would kill fuel pump ?

Good idea. On mine, I'm not crazy about the plastic connector that attaches to the sender on the block. It could be dirty or not tight. I will check into that.

That still would not cause the engine to cut out for a second I don't believe. There must be a short in the ignition system somewhere.

Spent several hours today removing and sanding every connection, and spraying electrical cleaner to every plug that I could find in the ignition or charging circuits. I wasn't finding much.

I did find a Mercathode system wire that had worn down to a bare wire, which I repaired, but don't think that would cause the problem I am having.

Finally decided to remove the battery cables. On the 4th and last one I found this.

I think this might be the culprit. It had worn to bare metal against the battery box and was probably shorting out on occasion and causing problem.

What do you think?

I'm going to ty and get it out this week to see if the problem persists.
https://cimg3.ibsrv.net/gimg/www.off...4bd9b724ab.jpg

RevdUp,

Is there actually a route to ground from that point? Even if my battery trays were made of metal, there'd be no connection to ground.

Thanks. Brad.

Good point. I think there is, but I will be checking into that.