Motor issues

[Cascadia]

Didn't know where to put this at. It involves a motor but the motor is in a boat. Not a rig.

Took our boat to pineview resovoir this weekend with family. It is an 02 centurion Elite V-Drive with a mercruiser 350 mag mpi. Boat ran great on Friday. The my son, brother, and I took it out Saturday morning. It ran totally normal across the lake. Probably a 20 minute ride. There was a wakeboard competition going on so we were just watching that. We sat for probably a half hour. Then we went to leave to go board ourselves. It fired right up but died shortly after (3 seconds or less). Fired it up again and the same thing. I have it some gas in neutral and fired it up thinking it would rev higher, but the same thing happened. I did this several times and it fires up perfect and idles for a sec and dies.

Eventually I started walking the boat back along shore, I had nothing better to do and it was cooler in the water. We called the sheriffs office and they sent someone to tow us back. Lucky for me I had registered the boat the day before. Otherwise I would have been SOL. Got it on the trailer and looked for any loose wires. It is a mercruiser 350 mag so its fuel injected. A lot of threads online lead me to the water separator (fuel filter). Drove into Ogden and picked one up, installed it, and tried running it. Same thing. Fires and dies.

Any ideas? I figure its pretty close to a chevy mpi 350.

 

[BoostedRNR]

I would guess a possible fuel pump or ignition switch maybe?

 

[Caleb]

Check fuses. If I remember correctly, there's only a couple on those engines and I seem to remember one of them will act similar to that.

 

[Cascadia]

I have checked all the fuses under the dash. If there are other ones I can't see I haven't checked them. I can't seem to find any other fuses though. Next on my list was to put a test light on the fuel pump. It's just been too hot to work on it.

 

[Caleb]

All of those efi mercruisers I've worked on have had a couple fuses back on the engine. Granted, all the efi ones have been swaps I've done so the factory ones may not have the same setup.

 

[Greg]

Rather than replacing parts as you go, your best bet is to start checking each aspect of what an engine needs to run. Fuel, Spark and Compression. Sounds like it will run when it wants, so you can rule out compression. The next thing you need to do is check that the engine IS making a spark when it's not starting. If it's getting spark when it's not starting, then it's more than likely a fuel issue.

If you're not getting spark and I had to toss out a Wild Ass Guess (and I don't know these motors), but I'd say check the ignition module inside the distributor. Most of the time when they die, they are 100% dead and won't fire. Sometimes they will do just what you're talking about. If the module is still good, I'd be looking hard at the coil.

Good luck and let us know what happens!

 

[I Lean]

I had VERY similar problems with my boat. Turned out to be the fuel filter had a small amount of air in it--enough so the pump was trying to draw air instead of liquid. In my case, the pump is directly after the filter, so the filter is under suction rather than pressure. The temporary fix was to carry a small bottle of fuel in the boat, to top off the filter when the level dropped. The permanent (hopefully) fix was a new filter that didn't leak air into it.

If yours has the fuel pump before the filter, then none of the above can possibly apply. Find the fuel pump relay and jumper it, so you can "manually" turn the pump on. If it works, then you can look for causes that would keep the computer from firing the pump. If it doesn't work, then you're more likely looking at the pump itself, or wiring/relay/etc.

 

[Cascadia]

I've been sick most of the day today. Everytime I've felt decent I would run out and try to work on it. Which would only last a few minutes. I was able to test the power to the pump and it does have power. I wasn't able to test more than that with feeling nasty. Hopefully I feel better tomorrow. I will pull the pump and see if it is seized. May sound like an idiot question but how do I check for spark?

 

[STAG]

I have a spark plug tester light that is basically a test light that goes in between the spark plug and boot