Engine Sputtering and then Won't Start
 

I have a 2001 Mariah Diablo with a 4.3 litre MerCruiser engine.

The very last time last summer I tried to take it out, it started fine and then just after I left the dock, it stalled. The engine would crank but not turn over. I took it home and tried a few days later while it was parked in my driveway (with the hose attached) and it ran fine and stayed running. I didn't have another chance to take it out until just yesterday.

I changed the plugs and wires before the season started and run it in my driveway again. Started up fine, stayed running, no issues. Started up better than it has since I've owned it actually, I think thanks to the new spark plugs, the old ones looked pretty worn. Got out on the lake and it ran great for about 20 minutes, then it started sputtering and stalled out. It wouldn't turn over again, I let it sit for 15 minutes or so and was able to get it to start again, but it was sputtering the entire time. The boat wouldn't move fast at all. It ran like this for a bit before stalling out again. I couldn't get it to turn over after that and got it towed in.

Just hoping for some advice as to what to check / fix here. I'm thinking I'll start with replacing the fuel filter but maybe there are other things to change too. If its bad gas, I'm not sure what I can do about that, as the tank is mostly full and I have no idea were I could put 20+ gallons of gas.

Re: Engine Sputtering and then Won't Start
 

When was the last time the fuel filter was changed? Sounds like you may have water in your fuel.

Re: Engine Sputtering and then Won't Start
 

I changed it not at the end of last season, but the end of the season before.

Will it be obvious once I remove it if water is in it or not? I ordered two replacement fuel filters (one for now, one as a spare) that will be arriving Thursday. It would be nice if I could determine if this really is the problem without having to strand myself out on the lake again or annoying the neighbors by running the boat for a long time in the driveway, although maybe that's what I'll have to do.

Re: Engine Sputtering and then Won't Start
 

When you remove the fuel filter, dump the contents into a clear container (glass). Let it sit. If you have any water, you will see it at the bottom of the glass.

Re: Engine Sputtering and then Won't Start
 

Thanks, I'll check that out hopefully when I get home.

Re: Engine Sputtering and then Won't Start
 

Had similar issue on my 4.3 would just about tick over on idle . Any load would cause the engine to die. Turned out to be a bad connection on the fuel pump.

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Re: Engine Sputtering and then Won't Start
 

Is there any trick to getting the old fuel filter off? I've even got one of those filter wrenches and the thing won't budge.

I'll look for some bad connections too, thanks.

Re: Engine Sputtering and then Won't Start
 

Never mind, got it off. Hit it with a mallet some and then just had to turn really, really hard.

Letting it sit right now to see what, if anything, is in the gas.

Re: Engine Sputtering and then Won't Start
 

I let what was in the fuel filter sit overnight and I didn't see any water in the jar. I'm not sure if that means that the fuel filter isn't the problem or not. I should be receiving the replacements today so maybe I'll run the boat in the yard for a while and see if it happens again.

I'm open to more suggestions in case that doesn't solve it.

Re: Engine Sputtering and then Won't Start
 

If there was water in the fuel filter you would have seen it in the bottom of the jar. So it sounds like you have eliminated that as a potential fault.
Is your engine carburated or fuel injected? I assume since it is a 2001 that it is injected. If fuel injected do you have a fuel pressure gage to monitor fuel pressure?
If you have low or no fuel pressure then what ChrisH mentioned could be your problem. You may have a loose connection in the fuel pump wiring, a bad fuel pump or a more common fault is a fuel pump relay that it on its way out. Check the fuel pressure, it should be around 40 psi or so. If it is good then perhaps your problem is ignition related.

Re: Engine Sputtering and then Won't Start
 

Its carburated actually. I don't have any fuel pressure gauges, just oil pressure and that seems fine.

Re: Engine Sputtering and then Won't Start
 

I couldn't find any loose connections. I replaced the fuel filter and replaced the ignition coil too (that seemed to be the other primary cause of issues similar to this that I found online). Ran the boat in my yard for 15 minutes without issues. I'm gonna try run it longer on Friday when i have more time and if that goes well, take it out on the lake. Running at idle in the driveway isn't really the same as running it under a load so I may be getting myself stuck out on the lake again this weekend but I'm not sure how else to really find out :/

Re: Engine Sputtering and then Won't Start
 

Sounds like coil collapse to me. You can ohm across the "+" and "-". It should be .6 to .8 ohms. This is the primary circuit.
Next, ohm from the center, high voltage hole, back to the "+" on the primary side. It should be between 9400 to 11,700 ohms. This is testing the secondary side.
After you get your coil replaced, which I'm confident that that is your problem, start the motor and make sure the "+" to an engine ground is LESS than 8 volts. This is testing that the ballistic resistor is doing its job of greatly reducing voltage to coil while it's running. Straight battery voltage will run the engine great but it cuts the life of the significantly.
Does yours have the ignition module in the distributor? If so, pull it out and clean up the contacts.
Good luck

Re: Engine Sputtering and then Won't Start
 

Thanks for the thread guys. I had a similar problem. I drained my tank, and then checked my fuel filter. See the attached pic. I believe I found the problem: water in the gas.

I believe the gas cap seal was rotten and/or the fuel vent did not have a "P" loop in it allowing water to get in the tank. New ones on order.

Re: Engine Sputtering and then Won't Start
 

Thanks everyone!

I went out tubing, water skiing, and just cruising around all memorial day and didn't have any issues. I replaced both the fuel filter and the coil, but I think it was likely the coil that was the cause of my issues. I didn't think to check the voltage of the old coil before I threw it away, that would have told me for sure it sounds like.

I did the same thing checking my gas but I didn't have any water in it like that. Looks like you've found your problem and hopefully solution too!