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Zombie Merc?-gctid406817

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    Zombie Merc?-gctid406817


    5.7 Mercruiser engine, 1999ish, fuel injected (SeaSport not Bay)

    Starts and runs on the muffs great.

    When he takes it out in 10 - 20 minutes it shuts down, no cough, no stutter, just running then dead. Will not restart till it cools down (last few times it has come back on the kicker. Local Merc repair guys changed some relays but it just did it again.

    I am thinking a bad coil.

    Any other thoughts from you wise people?
    Boatless at this time

    A veteran is someone who, at one point in their life, wrote a blank check made payable to "The United States of America," for an amount of "up to and including their life."

    Without knowing the system at all, I'd say shift interrupt switch activation(kills ignition), coil, distributor cap tracking (Which I would have expected to have been checked), ignition module, fuel pump.

    It would be good to carry a spare spark plug the next time out. If/when it dies, pull a spark plug lead, plug it into the spare, then crank the engine with the plug grounded on some bare grounded metal. This will tell you if you have spark or not and tell you where to focus your energy.



      there are easily several things that can cause this, one of which being the engine's computer (ECM). One way or another, you'll need to look at the basics--being is it fuel or spark? Do you have a spark tester? There are a few types, but they are pretty cheap and you should be in everyone's tool kit anyway (in my opinion). Is the engine just shutting off, as if you turned off the key really fast or hit the kill switch, no matter what RPM's you were at? Does the existing coil appear to be leaking or wet around the top? The coil can leak it's oil, then it gets hot and won't function until it cools down again. If the engine is indeed simply shutting off, without any sputtering, it could be fuel related or ignition related but you must go through a series of steps in a process of elimination. I wouldn't just start randomly throwing parts at it. It could be the sensor in the distributor, kill switch, ignition key module, the computer, fuel pump, or several other things.

      Either way, you should inspect the engine's computer/ECM. It should be a little black box about the size of a deck of cards, typically next to the distributor or hanging off an exhaust manifold/riser. This vintage of computer typically had a 2-piece black plastic case/housing, and they weren't sealed very well. And at least in my previous boat's case, it was installed in about the dumbest spot possible--right below the deck hatch drip edge so that any excess rain or deck washing would simply spill right onto the computer. Even the pretty plastic engine cover slanted and would drip water RIGHT ONTO the computer. Stupid stupid design.

      If I were you, I would unplug the harness on the computer, remove it from it's mounting bracket, and just try turning it around and seeing if any water drips out. If yes, that's likely your problem. If it's not actually the problem--it eventually will be. The updated ECM's are a one-piece black case and shouldn't allow any water in (maybe the engine already has an updated computer). The ECM's are not possible to diagnose directly other than you must test and eliminate all other possibilities first. When nothing else is left to test, the process of elimination states it's the computer. At least for my '96 Alpha 1 Gen2, it had a very nice flow chart to trouble shoot the ignition system. I knew to start with the ignition system because I bought and used that spark plug tester I mentioned. Whenever this stalling symptom would happen, I would not have any spark until "things cooled down" again. I have a long post about the Thunderbolt ignition issue from a few years ago that further explains it.

      I wouldn't just buy and throw a new ECM at it either without troubleshooting--they are typically very expensive, like $400-$500 depending on where you buy.