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Thread: 496 HO Mag Mercruiser - can ANYONE help?

  1. #1
    ParkerRiverRat
    This post has be x-posted in other discussions so I'm sorry if you've read this already!
    ok, our 2003 Cat is having problems... it's been in he shop for 8 months now and they STILL can't figure out what's wrong with it. So, if ANYONE has ever heard of this problem and has any solution, please let me know.
    Here's the problem...
    I have a 2003, 496 HO Mag Mercruiser Engine. The Engine stalls when run for approximately 10 minutes. Restarts but continues to stall. When the engine Analyzer is plugged in to ECM, engine will not stall but the screen of the analyzer will go blank when engine would normally stall. The screen will restart wen engine is shut off and restarted.
    We've already paid $3500 because it was supposidly a head problem, but that wasn't it...
    Also, we got a new computer because the Mercruiser people told us that might be the problem... and that didn't fix it either.
    If anyone can think of anything, or knows someone we could call who knows the problem it would help greatly! We've got a trip planned every weekend in June, so we really need it fixed by then.
    We're taking the boat to a new shop next week, but after talking to them on the phone they're not sure what's wrong either...
    Everyone's telling us they've never heard of this problem, but we're hoping in an engine that's 3 years old someone else has had the problem and can let us know how they fixed it!
    Thanks!

  2. #2
    Riverjet502
    Just a thought here is all? How about a phone call to "Merc" and see if they can give you some info or tests for your dealer to do to that would be more specific to your problem. A dollar to a doughnut says your not the first or only person to have this problem. I've done this with cummins and it sure helped me.
    Let us know what you find...

  3. #3
    Beer-30
    Has anyone checked the power cables yet? I have the same motor, but 2001. I haven't had cable issues on it, but on my dually, I would be driving along and it would die. It would restart, but some time later, die. Had it towed to the dealership. They tore the dash apart and found that the ground the stereo shop had used for the Clifford alarm was loose. The screw holding it to the metal had loosened. When I would hit a bump or turn just right, it would open the ignition circuit.
    I would look at every ground on the motor/batteries. Then, if all looked good, I would tap into the main power into the ECM and tie in a volt meter. Run as normal and see if the power goes away when it dies. That would confirm if the power was still constant to the ECM.
    Also power supply to the coils, maybe? It would have to be something that would kill all of them.
    Oh, ya know, it could be as simple as an ignition switch. Might start there with the volt meter and see if it is going open when it warms up from some current flow.

  4. #4
    Beer-30
    Just a thought here is all? How about a phone call to "Merc" and see if they can give you some info or tests for your dealer to do to that would be more specific to your problem. A dollar to a doughnut says your not the first or only person to have this problem. I've done this with cummins and it sure helped me.
    Let us know what you find...
    They don't do that. They tell a person to go to a dealer first; then they say they will step in if the authorized shop can't find it.

  5. #5
    phebus
    When I was talking with Bart at Alco Marine the other day, he told me of a problem with a boat stalling, but when hooked up to the scan tool, it would never stall. The shop had the boat for repair of the stalling problem, but everytime they worked on the boat, they had it hoked up to diagnostics, and they couldn't get it to stall, and recreate the problem. Finally the boat was run without the scanner attached, and the problem was discovered.
    I can't recall what the problem was, but call Alco, talk to Bart, and possibly your issue will be the same

  6. #6
    ParkerRiverRat
    Just a thought here is all? How about a phone call to "Merc" and see if they can give you some info or tests for your dealer to do to that would be more specific to your problem. A dollar to a doughnut says your not the first or only person to have this problem. I've done this with cummins and it sure helped me.
    Let us know what you find...
    We've actually talked to the Merc people a few times and so has the person who was been working on the boat the past few months... they're the ones who gave us a new computer thinking that was the problem, they gave us the computer free but that didn't fix it. They've also been claiming they've never heard of this problem.

  7. #7
    phebus
    I assume they have hooked up a pressure gauge to the fuel rail to rule out a vapor lock problem?

  8. #8
    ParkerRiverRat
    I assume they have hooked up a pressure gauge to the fuel rail to rule out a vapor lock problem?
    We're not sure that the guy who's working on it did anything "for sure" but he claims he's been over everything and can't figure out what it is. We'll add this to the list though! Thanks!

  9. #9
    Jbb
    I have seen a problem similar to this .....and it was something in the fuel tank partially covering the pickup...

  10. #10
    ParkerRiverRat
    When I was talking with Bart at Alco Marine the other day, he told me of a problem with a boat stalling, but when hooked up to the scan tool, it would never stall. The shop had the boat for repair of the stalling problem, but everytime they worked on the boat, they had it hoked up to diagnostics, and they couldn't get it to stall, and recreate the problem. Finally the boat was run without the scanner attached, and the problem was discovered.
    I can't recall what the problem was, but call Alco, talk to Bart, and possibly your issue will be the same
    Alco is actually the new place we're taking it too... So, hopefully they'll be able to fix it then! We'll give them a call though too! But we're supposed to drop it off over there in the next week! Thanks!!! That gives us hope that it might actually be fixed this time!!!

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