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Mercruiser 5.7L suddenly stops

D

DRichards143

New member
Let me start by saying THANK YOU to all of you that are knowledgeable about boat engines and are willing to share some of that wisdom with those of us who are clueless.

I have a 2000 Formula 27PC with Twin Mercruiser 5.7L engines. After about a 1 hour ride this past weekend, the port engine suddenly stopped running. I tried to restart it and it cranked over fine but would not start. I let it sit for about 2 hours and then tried it again - no luck. I checked all connections around the main module and distributor cap to make sure everything was secure since it seemed the problem was electrical (shorting out?). All fuel pumps, etc. seem to be working fine. After 2 days of sitting, it started again and ran great. I took it for about a 40 minute ride and it died again. Same symptoms - cranks over fine but will not start.

Does this sound like an ignition sensor? A short in a wire (tachometer, etc.)? Any suggestions on the best way to troubleshoot the problem?

Thanks in advance for any suggestions.
 
Hope this is helpful until someone more experienced with your set up chimes in. I know how frustrating this can be so good luck!

Remember that an engine require three things to run. Loss of compression, fuel, or spark will cause it not to run so be sure to check them before just poking in the dark etc.

Since it does run compression is most likely not your problem, so check on the others first.

I know it will be difficult to test since it needs to run for a while before the problem shows its ugly head, but before you get to changing every easy access part just confirm that the carb or FI is supplying fuel, and that the plugs are firing.

No marine mech here, but when I have had similar issues it has turned out to be either the module or pigtail wiring harness that plugs into it. I have actually had to replace both more than once on the same engine so it is not unusual etc.
 
Determining if it is a fuel or ignition problem is the first order of business....When the motor will not start, remove a plug wire and insert an old spark plug...lay the plug on the block and check for spark as you crank the engine. If you have spark at the plugs, it is most likely not an ignition problem. Another test would be to use a shot of starting ether...spray it into the flame arrestor. If it starts it is a fuel problem.
 
Thanks for the feedback. It turns out it was the ignition sensor. It is located under the distributor cap. This is a known problem for the older Mercruisers. In fact, the new replacement part was significantly different than the original. The part cost $70.

Thanks again and I hope this can help someone else out in the future.

Dave
 
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