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Mercruiser 50 Alpha Shuts down while cruising wakeboarding

cosmo

New member
"Hello All,
I'm new to th


"Hello All,
I'm new to the board. I have a 2003 Maxum that I bought new. It has a 5L Alpha MPI engine that runs great, starts great, plenty of power for my needs.

Howevever I have a recurring problem since we bought the boat. The engine shuts down without any notice, when we are cruising, wakeboarding, high speeds, low speeds. We could be crusing for a few minutes, or for half an your, and then all of the sudden, it's like someone turns the key off. I put the shifter in neutral, starts right up, and we go again. I get a skiier up, and then it dies. You can see the danger here.

My local Mercury shop has replaced the cap and rotors two years in a row, and no success. We just got a new cap and rotors, and all the service bulletins done. Still have the problem. The first year we got the boat, the Maxum dealer replaced the fuel pump, no success.

The Mercury rep is going to be in town next week, and wants to re-flash my computer. What does this do? I think it might be a computer problem because the engine runs great.

Some people have said it may be the kill switch. There is no pattern as to when this dying happens. Any ideas?

Thank you."
 
"I would suspect the shift int

"I would suspect the shift interrupt switch. With an MPI engine its a NC switch, so if it is flakey in any way, or the wiring is iffy, you can easily get extraneous engine outages. Check the switch in forward, neutral and reverse; it must be centered in the V notch. If not, the cables need adjusting.
Rod"
 
"Rod,
Thanks for your feedbac


"Rod,
Thanks for your feedback. I discussed the shift interrupt switch with the repair shop, but not sure if they changed it as one of the Mercruiser service bulletins or not. To clarify, this shut down is happening while in gear and cruising, and not when shifting. However, it does seem to happen often when pulling a wakeboarder out of the water. The rider gets up, and then the engine dies. It also happens when cruising.

The Mercruiser rep wants to reflash my computer, but I hear that only deals with fuel mapping, and not any engine shut down.

Thank you for your feedback."
 
"Rod and Cosmo:

This proble


"Rod and Cosmo:

This problem has been ongoing since it was new. The dealer has no idea where to look and keeps replacing the same old "good parts". The dealership will not put a technician on this type of "search" problem due to the labor involved.

Rod, your idea of a flakey shift interrupt switch circuit is a strong probability. My noggin leeds me to think that there is a loose ignition wire in the harness, most likely in the engine area, that has a weak connection. Engine vibration causes the weak connection to fail momentarily. Most likely a loose pin in a connector when inspected that looks normal but when reconnected does not make a solid connection. Thus the intermittent engine stall.

The way that I look for these gremlins is by carefully checking each connector involved with the ignition. I have used a magnifying glass to look for arcing on pins in connectors and also pull and push each pin in a connector. It is time consuming but sometimes is the only way to find the fault. I also will look at the back of a harness plug (both sides) before disconnecting it to see if one or more of the push pins is not all the way inserted. By studying the schematic beforehand, I can get the probable areas of fault.

Cosmo: You can do the push/pull wire search while the engine is idling. You can also do a wire wriggle test at the same time. When it dies or stumbles on you have hit paydirt. Good luck."
 
"Guy,

Thank you as well for


"Guy,

Thank you as well for your information. I am fairly technical, so I will study the ignition diagrams in the manual and to the unplug and plug in thing. I believe it to be an electrical issue as well because everything else works great.

The Mercruiser rep wants to re-flash my computer. Not sure if there could be a bug in the system causing the fault, or if the re-flashing has nothing to do with this type of item. My Mercruiser repair shop sais there are a few tech bulletins on this, but their fixes as of two weeks ago had no affect on the problem.

I'm also thinking about replacing the kill switch just to rule it out. I have seen a few postings about faulty kill switches causing this type of problem.

I'm tired of throwing money at the problem to "see if it fixes it" as my repair shop says.

Thank you very much for your thoughts, I will be printing this when I see the Mercruiser rep next week."
 
"Cosmo;
I'm with you; I d


"Cosmo;
I'm with you; I don't think a reflash will fix your problem. Dealers often revert to a reflash with an EFI engine, hoping that will fix the problem. There was a post a few weeks back of a 5.7 that was reflashed for some reason, and it ran like crap after that. Developed a serious miss in the 2000 to 3000 RPM range.
You have an intermittent electrical gremlin as Guy says; and these can be a real bear to isolate and locate. Usually when you and the tech are testing it, it will run perfect.
I think changing out the interrupt switch is a good idea, just to rule it out. Keep the old one as a spare, you may very well need it one day.
I like Guy's idea about wiggling and pulling at various wires while underway. You may have to be at cruise power to properly simulate the failure.
Pay particular attention to the 10 pin engine harness plug. Sometimes moisture gets in these and corrodes the wires, causing all sorts of grief.
Rod"
 
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