Mercruiser sometimes not starting and cutting out at RPM

[askiopunk4358796652]

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

 

[achris]

Hello askiopunk4358796652, and :welcome: to iboats.

Need a few more details. Do you instruments stop working when this happens? Have you cleaned the battery terminals, both positive and negative, and the cables on the engine, including the grounds?

If you've done those things, then check the 10 pin instrument harness connector at the engine, make sure it's clean, and the terminal pins are in good condition. Check the instrument fuse, a 20A glass fuse. (I prefer to replace those with a blade fuse and holder). Also check the wires and condition of the 'kill' switch...

Cheers,

Chris.......

 

[alldodge]

Agree need more info as to what is happening
Need a voltmeter and hope your unable to start long enough to find it. It could be as simple as the key switch.

 

[askiopunk4358796652]

When I go to start it all the instruments work and the buzzer is going off but when I turn the switch nothing happens. Sometimes it works for a while. Same thing on the water- sometimes it's fine but sometimes it cuts out intermittently. Just completely shuts off and surges.

Starter keyswitch has been replaced. And like I said- all lights/instruments/horn work fine all the time- it's just the engine that cuts out for some reason.

 

[achris]

You need to start probing around with a test light.

Hook the test light ground to the battery and probe the coil+. Then connect the test light to the engine block and probe the same point.

Chris......

 

[alldodge]

I'm seeing a Sanger V210 as an inboard and you say late 90's which makes me think EFI. Have a serial number?

 

[alldodge]

Just noticed your other thread about the transmission grinding in reverse, boat is a 97

 

[askiopunk4358796652]

Ok, after *considerable* troubleshooting we finally found the problem... an intermittent ground to the start relay. 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 not we need to track down where the actual break or loose/corroded connection is so we'll do that next.

Hopefully this helps someone else with this same symptoms and thanks for all your help!