‘03 21i rough starting, stalling 350 MAG MPI.

[chuckhoenig]

With the wounds of our stolen stereo equipment still fresh, it’s back to work on the normal stuff.

Last season the boat ran great until the end of the year. That’s when i had issues but with hard starting, and then stalling. Had to get towed out of the water at the end of the season.

I’ve had fuel pump issues in the past, looked into that being the likely culprit. I’ve got pressure on the rail 32-35psi, and both pumps are pumping fuel. A few years ago I had to replace the fuel pick up tube in my fuel tank as it wore out, but that affected the pressure in the rail. I’ve also replaced the IAC valve, but that was 2-3 years ago.

Knowing this I figured ignition issues. I check the distributor cap, and it was really corroded.

Yesterday I changed the spark plugs, cap, rotor, impeller, oil, and fuel water separator (poured it into a clear cup, no water in it)

Still happening.

I pulled the ignition coil last night, it was fairly corroded on the post leading to the DC. I cleaned it with a wire brush, reassembled, still happened.

Afterwards, I checked the spark on the ignition coil post with a tester, also checked the spark from the coil wire. Both looked good. I suppose it could be a bad coil that heats up (read an old post about this) and then delivers poor spark. Wonder if y’all have any ideas before I pony up $300 on a new coil.

I did see a post about the tachometer causing a ground issue, I’ll check that today. Or I suppose it could be related to the injectors.


Thanks!
Chuck

[chuckhoenig]

I didn’t see anything that looked odd around the TACH today, but did put this inline spark plug light in. Got the boat running, played with the throttle a bit, and you’ll notice, I lose spark, and the engine dies.

I also checked, I’m getting power to the coil, and I’m getting power to the Ignition Control Module. Also looked at the Throttle control Module, I’m getting power there, and also have a good ground.

With video attached I’ve got to assume it’s spark related.

Chuck

[chuckhoenig]

I’ve done all the troubleshooting I think I can do. All of the guides I’ve been using from easy auto diagnostics.com checked out. I took the boat for a test drive on Tuesday, and it ran excellent. Ran it for about 20 minutes at various speeds, including 35mph at 3500rpm. All good

Went out on the lake today with my family, and it was a little hard starting. Then, after it started I didn’t have any issues, until we left the marina out of the no wake zone. We put the tube out, began to toe my sons, and it quit. No sputter, no misfire, just died. Then it wouldn’t start. Someone was nice enough to tow us to the marina, and then I checked ignition wires, spark etc, but would start, then it did. Left it running for a bit, then went back out on the lake after starting it about 8-10 times just to be safe.

Same thing happened, only no kids on the boat. I was able to limp it in back to the marina. A mechanic told me it could be my ignition switch, so I changed that out. He said that if the tumblers are bad, then they could create a short while underway.

I changed it, and boat started fine. Started over and over all fine. Let it run for a bit, and fine. I also noticed that the neutral safety switch had a loose wire, and I tightened that. Not sure of that was the problem all along. I didn’t test it as I didn’t want to get stuck again. I was able to idle to the boat ramp and pulll it out without issue.


Now I’m completely stumped.

One last note, I did change the starter solenoid and the 50 amp breaker on top of the engine last year, so I don’t think that would be my problem.

Please help, if I don’t get this boat running, my next post will have a for sale sign on it.
Chuck

[boatwakes]

Hey Chuck, it's ignition module inside the distributor. Here's the part number
SENSOR ASSEMBLY (#87-892150Q02). It fits just below the rotor. Original units have two wires; one is white with red stripe and the other white with green stripe. The new updated version has a third black ground wire and the units are potted to be waterproof.

[chuckhoenig]

Boatwakes,

Thank you for the response, but I don’t have a sensor assembly on my distributor. Unless I’m looking at the wrong schematic.

https://www.perfprotech.com/mercury-...40?umodel=4922

Merc 350 MAG MPI, serial #0M392193

Thanks,
Chuck