2002 Mercruiser 6.2L Horizon MPX EFI-Won't start warm/stalls after warm restart

My last three experiences:
1-Started fine, ran boat for 45 minutes, sat for 45, would crank but not start.
2-Seven days later, started fine, ran for 30 minutes, sat for 45, started fine, ran for 5 minutes and stalled while up on plane. Would crank but not restart.
3-Seven days later, started fine, ran boat for 30 minutes, sat for 20, would crank but not start

For the seven years I have owned the boat, the starting process has always been
-crank, crank, crank, crank, start
since this problem has surfaced it has been
-crank, start (ignites much quicker than before)

Mechanic thinks "no" on vapor lock and is going to replace the ignition module.....

Any ideas? The change in "cadence", if you will, on the ignition process is puzzling...

Mechanic thinks "no" on vapor lock and is going to replace the ignition module.....

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Why? What tests did he perform? I would first look for loose or corroded wire connections and swap out the fuel pump relay since you don't know if it was from a lack of fuel or spark.

any alarms, did he read the ecm, did something build a big clog in your fuel vent.

Seanfranc said:

For the seven years I have owned the boat, the starting process has always been
-crank, crank, crank, crank, start
since this problem has surfaced it has been
-crank, start (ignites much quicker than before)

...

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Can you think of anything new that has been done or changed out to the boat or engine since you noticed the no start situation?

For example, A tune up of some kind, New battery + CCA, Engine timing, Outside temperature, Fuel grade or and fuel station.

The list could go on, anything new between now and then?

No alarms....the only thing I can think of different, and this is probably a reach, is that I normally keep the fuel tank 40%-60% full. This started after I filled the tank completely. I am now down to a little more than 75% full and it is still happening....

Try this simple test first; try pulling the fill cap off and listening for a vacuum when the issue happens again. If there is, you have a blocked vent as mentioned earlier. Could be spider webs etc. could also be that the fuel vent line is run incorrectly, has a valley, and now has fuel in there since you've filled it up. The other thing you may want to try if the vent isn't clogged, is to isolate the engine from the vessel and hook it up to a portable fuel tank. Run as you have been. If the problem doesn't arise again, the issue is the vessel's fuel supply system; dirt in tank clogging pickup, antisiphon valve, colapsing fuel lines, water in fuel, etc, etc.

Seems like your mechanic is leaning towards an ignition issue. he may be right but how did he arrive at that, did he check for spark right after the issue occured or is it just a hunch?

I'm hoping its the fuel vent, but if you run on a portable tank and it still happens put a few ice cold beers( or equivalent) on the ECM and see if that fixes it, could be the ECM going bad. Hope like WoodieMan says you here the swishing sound.

After each of the first two times this happened, the fuel filter (seperator? The spin on one) was removed and examined. The boat started each time subsequent to that. Maybe the breaking of the vacuum is what is allowing it to restart and run for a while? I will check it this weekend. Thanks

Mechanic went to the boat, it would not start, he replaced the ignition module and it fired right up. Hopefully that's all it was....

nice, happy boating

Seanfranc said:

For the seven years I have owned the boat, the starting process has always been -crank, crank, crank, crank, start.

since this problem has surfaced it has been
-crank, start (ignites much quicker than before)

Click to expand...

Seanfranc said:

Mechanic went to the boat, it would not start, he replaced the ignition module and it fired right up. Hopefully that's all it was....

Click to expand...

It would be interesting to know if the engine starting time went back to the old -crank, crank, crank, crank, start, or does it still go -crank, start with the new ignition module sensor???

Spent a wonderful, trouble free, day on the water yesterday......it's back to crank, crank, crank, crank, start.......thanks for all the thoughts on this one...