MerCruiser MCM 5.0L MPI Randomly Shuts off at higher RPM

[jrneal1]

I have a 2002 MerCruiser MCM 5.0L MPI. The serial number is 0M520231. When I bought the boat about three years ago from a dealer and it was having the same problem. It will idle and run at lower RPM without any issue. However, when I get to 3000 - 4000 RPM range it will randomly just shut off (like someone hit the kill switch). This past Friday, the lake was calm and the boat ran all day without even a hint of an issue. Saturday, it would hardly run for 5 mins without shutting off. Once it dies, I can immediately put it in neutral and start it right back up.

This same issue existed 3 years ago when I was looking at buying it from a dealer. They tried replacing the throttle cable, ignition coil and interrupter switch. After that, it has run like a top until now.

I haven't kept close track of this, but the only thing that doesn't seem random is the condition of the water. On Friday the water was relatively calm and there wasn't a lot of boat traffic and it ran fine. On Saturday the water was turbulent with lots of wakes and boat traffic and it struggled mightily. I just checked to see if there was water in the fuel filter and / or in the fuel tank. it was straight gas. I'm a novice, but willing and eager to learn.

 

[alldodge]

Howdy
The SN listed is for the outdrive, but should be good enough to know what you have

When you removed the filter did some spill out as being really full, or was it a bit below full?

Has the distributor cap been changed?
If not would suggest replacing it only because while it may not be the issue this time, the caps are known to go out without warning. They can look perfect and still be bad. Keep the old as a spare

On the timing chain cover there is the crankshaft position sensor (CPS). Remove connector and clean contacts

Check full pressure at the rail. Should be able to get a loaner from the local auto store

 

[jrneal1]

alldodge it was full and started pouring out as soon as I started tilting it to empty into a jar. Do I check that pressure while running at 3000+ RPM or at idle or both? Thanks for the tips!

 

[alldodge]

There we go 0M353273

Fuel pressure should be
Turn ignition ON don't start = note
Running idle = note
Watch pressure as rpms increase under load (not on a hose) up to WOT

 

[tpenfield]

Might actually be the kill switch . . .

 

[jrneal1]

tpenfield are the kill switch and interrupter switch the same thing?

 

[Searay205]

no the interpreter switch kills spark when shifting from foward to neutral or reverse. without it you pull the gear lever so hard it goes past the selection you want. for example if i was in forward i would pull the lever so hard it would go to reverse skipping neutral. don't ask how i know.

The kills switch is what you tether to your life jacket in case you fly out of chair. it cuts the engine off. a twitchy kill switch could cause your problem. the interrupter only activates when shifting.

 

[jrneal1]

alldodge I'm curious as to how why you're saying the serial number for the transom is the engine serial number. i'm not doubting you, I just can't connect the dots... and as I do research i want to make sure i'm using the correct number in my searches.

 

[alldodge]

I'm just plugging the numbers in and this is what its telling me. Wouldn't be the first time the numbers were mixed up. A person gets the numbers and has label printed and messed them up

Look them up at the Mers site
https://www.mercurymarine.com/en/us/parts-and-accessories/parts-catalog

 

[jrneal1]

I didn't get to use any test equipment last night, but I did take the boat out. Left the marina and throttled up to 3500 rpm and ran it for about 10 minutes. Floated for a couple of hours and then ran it for 15-20 mins at a steady 4200-4500 rpm. it ran perfectly. rough water is starting to become a key factor into the issue. could it still be a fuel issue? or in light of this observation is it more likely to be an electrical issue? could it be that the water in the hull not pumped out by the bilge is splashing on some electrical component shorting it out?

 

[tpenfield]

When the engine shuts off all by itself and won't re-start. . . . take the leads of the kill switch and connect them together and see if the boat starts.

 

[jrneal1]

tpenfield so, that's the thing. it always restarts immediately. I can darn near still be on plane and before I coast down, I can kick it to neutral and it will start - every time. I've had days where it will die 10-15 times and it has immediately restarted. the only thing different this year than the previous two that I've had it is that this year i have it in a slip. For my next test, I may pull it out and let it dry out and then take it out on a crowded day. this may help point to the issue.

 

[tpenfield]

I'd replace the kill switch to take it out of the equation.

 

[QBhoy]

So...please change the diz cap and rotor. Man I mist sound like a broken record by now. Haha.
That said, I had an issue with the interruption switch. But only at full throttle it happened. Slight adjustment and it was sorted.

 

[Searay205]

I suggest have someone work the throttle full stroke (engine off) and watch the shift interrupter switch. It should not engage at all if it does it could be the problem. shift interrupter switch works by the force generated on the shift cable when your changing gears. The throttle should have zero effect. So place in drive push throttle wide open i would have them work it full range back and forth make sure shift interrupter doesn't move. do in neutral and reverse

 

[jrneal1]

It seems that the boat gods are not without a sense of irony. It appears that my issue was the diagnostic plug. it doesn't have a cap on it and it was unsecured. I believe the positive pin (purple wire) was shorting to the engine block. I secured the plug and ran without any issues for the first time in a long time. I'll report back after several more outings.

 

[jrneal1]

Well, here we are a full year later and I finally have the answer to my problem. Posting just in case someone else ever runs into the same issue. Mercury issued a service bulletin back in 2003 (attached) pertaining to No Start, Engine Miss-Fire or Engine Shut-off Conditions. I shorted out the shift interrupter switch and the engine ran like a champ. Reconnected the switch and it ran like garbage. Issue is with the ECM and needs to be replaced. The attached document has a range of serial numbers for several different models. Yours might be in there if you're having an issue similar to mine.

 

[JorisvdHeijden]

Well, here we are a full year later and I finally have the answer to my problem. Posting just in case someone else ever runs into the same issue. Mercury issued a service bulletin back in 2003 (attached) pertaining to No Start, Engine Miss-Fire or Engine Shut-off Conditions. I shorted out the shift interrupter switch and the engine ran like a champ. Reconnected the switch and it ran like garbage. Issue is with the ECM and needs to be replaced. The attached document has a range of serial numbers for several different models. Yours might be in there if you're having an issue similar to mine.

Hello, I have exactly the same problem. My question to you : how did you short out the shift interuptor ?
Thanks for your reaction
Greetz from Holland