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Old 08-05-2018, 08:14 AM
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Location: Chicago IL area.
My Boat: Htm Sr-24 Ilmor
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Post New & Need help.

While driving my boat down the river. (boat has an ilmor mv-10 625) regular cruse 45 mph. Good temps, good plane, 50 psi on the fuel pressure.
The boat will like cut out and the RPM's will drop slowly, then kick back in, without touching the throttle. Fuel at 50 psi constant.
I put two new marine interstate batteries in this spring. The motor turns over just fine, so I think there is enough power in them.

We just had the high pressure filter and fuel pump changed, and it still does it. Off and on.

Is there anything with the alternator, or something that may run off of it that would cause this?

Its my understanding (prob. not right?) That the batteries, start the boat. Then the electrical system should run off alternator.?

I did my best to check the wires on the alternator, all seem tight and good. Would a failing alternator, do this?

It seems as if its an electrical or power issue. Any insight would be very appriciated.
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Old 08-05-2018, 08:25 AM
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If the alternator, or a wire from/to it were failing off and on could this make me loose power for 3-4 seconds?

I don't know much about motors, ect. but it just seems like if it were a fuel issue, the psi would drop off and on.

If it were the batteries, they would fall to a low level, but not come back in 3 seconds.

All plugs / wires were checked and good, according to MC of Chicago.
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Old 08-05-2018, 09:19 AM
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I would say, weak ignition coil, wire(s) or bad connection to the coil

Your other threaad indicates the temp was up to 235 degrees, was this also going on when loosing power?
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Old 08-05-2018, 01:56 PM
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No temp issue is after 3-4 min WOT runs. I can open the hatch for a couple minutes, Idle around 1200 RPM, and she cools right down to under 100 deg. So, Im assuming the sea pump is working as it should.

I will look around for the ignition coil, and see if I can find a loose wire. I really appreciate the help in a direction.
Im pulling my hair out. Im by no means a mechanic, but I guess its time to learn.
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Old 08-05-2018, 04:04 PM
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As a non-expert on the Ilmor V10, I do believe they have a coil for each cylinder in multi coil packs (6 and 4). If you can get a timing light on the wires to see if when it drops out is one or more of the coils getting weak. Wish I could be of more help but have only looked at the motor, never worked on one
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Old 08-05-2018, 08:23 PM
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Thanks for all the info, I added changing out all the coil packs, wires and plugs to the list.
Only hope to get her back to use a little more this year yet.
Thanks again for all your help, but this is way above my pay scale at this point.
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Old 08-05-2018, 10:52 PM
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I had zero intention of becoming a boat mechanic myself, but it seems to be a necessary evil to enjoy the sport. A fuel clog at the very end of the line wouldn’t necessarily register on the guage, but my guess is ignition related as well given how inconsistent the issue is. And that’s strictly a guess. Best of luck!
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Old 08-06-2018, 01:56 PM
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yeah, thats my best guess swell. Just dropped it off to have the ing. coils, wires and plugs all replaced. And what ever else there is in regards to the ing. system.
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