I/O Engine runs fine for 1 1/2 hours and then quits

Hi Folks,

This one seems to have my mechanic baffled, so I would appreciate any possible assistance. I have a Mercruiser MC 898R in a 1984 Searay. This season she has the annoying habit of starting up, going about 1/2 or 2 hours just fine on plane, and then I bring her down to slow or idle and after a few minutes the engine quits and won't restart. First, the mechanic replaced the ignition sensor. The next time it happened, he replaced the the ignition coil which he said was cracked. It happened again. Now he's scratching his head. He thinks that there is a short somewhere causing the failures and he thinks all of the wiring harness shoule be replaced. That would cost more than the boat is worth- not going to do it. I was wondering if any of you might have some ideas and would greatly appreciate some suggestions

Re: I/O Engine runs fine for 1 1/2 hours and then quits

How long does it set before it will restart?
When it doesn't start, have you checked for spark? Or checked the carb to see if there is fuel to the accelerator pump?

Re: I/O Engine runs fine for 1 1/2 hours and then quits

Not overly familiar with your engine, so does it have an electronic choke or a mechanical, thermatic choke?

If it is choking a hot engine that could be the problem.

Might want to consult a different mechanic...

Re: I/O Engine runs fine for 1 1/2 hours and then quits

The engine never did start up again. I went and tried it 2 days later, it cranks, but no spark. The mechanic thinks that it is perhaps a faulty ground somewhere that might be causing a short in the ignition coil and/or sensor after an hour and a half or so, but it will be a problem to find that. Don't think it is the choke. The boat is an '84, so the wiring is kind of old. But this seems to always happen after it runs for about 1 1/2 hours- he is still a bit baffled.

the choke is thermatic, BTW.

Re: I/O Engine runs fine for 1 1/2 hours and then quits

If you don't have spark, and it hasn't started again, don't start throwing parts at it again. Do some troubleshooting.