SB

Has it always done this since you owned it ?

Does it always do this at same exact rpm ?

you mention fuel filter change and was better for a bit. How old is any of the gas and guess how much of it ?

do a fuel psi test under wide f’n open at/past the rpms during issue ?

what exhaust ? Factory Y pipe still there ?

Bstocky

It just started this mid season. I’ve owned the boat since 2018. When I did the filter and new plugs the issue went away. Now is back. Doesn’t do it at the same rpm, it is sporadic, it’ll get up around 5,000 but will cut in and out through the rpm. Only tried twice. Didn’t want to push it. Haven’t ran any tests with fuel psi gauge yet, going to get a scanner on it as well. I’ve ran a few tanks through this season, all non eth gas, filled with gas sunday am. Emi thunder exhaust, factory y pipe in place with the silent choice still

Bstocky

Have been working on it for a little bit tonight, popped the cap off and noticed the rotor seems
to have some wear into it. Not sure if it’s enough to cause this issue?

Griff

I'm having a VERY similar issue with one engine(502mpi). It was random last year but happened nearly all the time this year. Most of the time it was doing it at 3400rpms for me and pulling back to 3100ish. Did all the normal basic stuff with no changes. Finally ran it under load with a Techmate hooked up. The end result is something is causing it to think its hitting the rev limiter. Everything else on the Techmate was normal except MAP sensor was slightly low on voltage. Swapped ECM's and no change. I didn't have much time mess with after that, but I did check the wires coming off the coil and moved them around a little. The upper wire harness for the coil seemed very tight and I got it to free up some. I'm assuming the ECM gets its rpm signal from this harness. Went out and ran the boat after that and it was holding 4400rpms evenly on both engines. The props (spares and +2" pitch from my normal ones) I have on will only spin to 4600rpms at best and due to water conditions, I really couldn't trim out enough to hit max WOT rpms. Bottom line, is I'm pretty sure I have short in that section of my wire harness. I'll be digging more into it over the next couple weeks.

I will say though that I have the MEFI 3 and Cool Fuel and you most likely have an MEFI 1 and VST system

Bstocky

I have cool fuel. No mechanical fuel sea water pump, no vst tank.

Drewm3i

Sounds like the tank vent or anti-siphon valve. Sounds like a fuel starvation problem.

pouliotk2441

Mine was doing this a few weeks ago and the only thing I found was one of the main harness grounds was broken out of the connectors. I fixed it and it’s been normal since. Not sure if it’s a coincidence but it certainly seemed more electrical than a fuel issue to me

Bstocky

.

are you talking the ground connections on both sides rear of the engine block? Or a ground in a harness connector?

Bstocky

Vent should be clear, I always put my finger by it when fueling and check for air pushing out.

Griff

That's exactly what I thought for mine originally as well. I thought I had a cool fuel pump getting week, but my fuel pressure held steady at 41psi.