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Mercruiser electrical issue

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sigmatero

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Have something crazy going with my late 90s Sanger V210 Mercruiser 5.7L. Sometimes it won't start with the key and I have to short circuit across two terminals on the engine. Usually goes in spurts (like won't start with the key for a dozen times) and then it will start again for a while. And it will run fine sometimes on the water and then it will just cut out like and then catch and run and then cut out. This is usually at a bit higher RPMs. It's definitely cutting out like an electrical switch has been shut off (not a bad running engine IOW). The engine runs really smooth and nice other than not starting and the cutting out.

I'm pulling out my hair trying to figure out what's going on. Not the start switch- replaced that. Plus I've wiggled about every wire in the boat looking for a short or open circuit.

Ideas?

Thanks so much! And my kids REALLY thank you since they're not able to go surfing
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Have something crazy going with my late 90s Sanger V210 Mercruiser 5.7L. Sometimes it won't start with the key and I have to short circuit across two terminals on the engine.

What 2 terminals? the large ones .There the main power for the starters solenoid. The small ones, they get power from the ign switch on start, yellow/red from switch, and black to ground. No power or no ground and the solenoid wont do its job
 
They are big terminals on top of the engine (two nuts). All of the instruments are powered and the buzzer goes off but the engine won't start unless I short these terminals. Though for a while it will start just fine with the key. Seems to run in cyles. No start for maybe 20 times and then start for 20 times.

But the real bugger is why it's cutting out when I'm running the boat down the lake. It just completely shuts off and then kicks back on and then shuts off. Surges. I've worked on engines all my life and it's not cutting out because of air or fuel- it's definitely spark. Something is shutting off all spark to the engine (not just a few cylinders like a plug or distributor issue).

I have a hunch the same intermittent issue that is shutting off spark to the engine is also shutting it off when I'm trying to start the engine sometimes. I just can't figure out what it is!

Also, when on land and hooked up to my water hose the engine has never shut off (or surged) at any RPM so it seems to be happening under load when on the water. Not sure how this correlates with the engine not starting though since that happens both off and on the water sometimes.
 
If you shorting the big lugs on this ,its the slave. shorting the big lugs only proves you have the power to operate the starters solenoid. The yellow/red from the ign switch AFTER is goes thru the neutral safety in the control box goes to the small lug here, the other small lug is ground. If it just clicks with the key, the solenoid is bad. If it dosent click it may not be getting the 12v from the dash.
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Sounds more like the main relay....without ID'ing the engine (or the parts being jumped) it can only be a guessing game...
 
Thanks for the help. Yes, I am jumping the slave to start it. I replaced the key switch and slave. Is there something in the boat that will disable the engine outside of the diagram you have shown? It's like something is telling the engine to shut off. Something is doing it sometimes while I start it and sometimes when I'm driving it.

The bad thing is that it's intermittent so really hard to track down.
 
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sigmatero said:
Thanks for the help. Yes, I am jumping the slave to start it. I replaced the key switch and slave. Is there something in the boat that will disable the engine outside of the diagram you have shown? It's like something is telling the engine to shut off. Something is doing it sometimes while I start it and sometimes when I'm driving it.

The bad thing is that it's intermittent so really hard to track down.
Click to expand...

Check the lanyard switch, if you have one for the shutting off while driving. If you are still having intermittent starts and can start the engine by jumping the slave, you have to check all connections between the key switch and the slave. That includes the ground on the slave.
 
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Ok, after *considerable* troubleshooting we finally found the problem... an intermittent ground to the start/slave relay [black wire off of "C" in the really helpful diagram above]. The reason it was such a bugger to diagnose is that it was intermittent. This was causing it to fail to start sometimes and also was cutting out while we were driving. We were able to jump it to ground and run the boat just fine so now we need to track down where the actual break or loose/corroded connection is so we'll do that next. Thanks for all your help!
 
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