I've got an issue with my starboard engine cutting out. The engine is a 1995 502 efi with 252 hours.

Ititially I noticed that when I was crusising @ 3,000 rpm's the starboard tack would bounce back down to 2400 rpms and then back up to 3,000rpms irratically. If I slowed to 2600 rpm's the tack still danced and lost power accordingly. Now if I bump it up to 3500 Rpms or above it is fine and runs like normal.

I initially noticed this last time I used the boat but after we stopped for lunch it didn't do it again (Nor did it do it for the rest of the weekend). Then this weekend it did this when I first went to get on plane plus, when I first fired the engine It killed a couple times and I had to refire with it eventually idleing correctly.

On Saturday after it did this I stopped @ a friends and he and I Installed a new water seperating filter (the other one only had 15 hours on it). After we did this we cruised up to a watering hole and everything was normal with no issues at all. Then on the way home from lunch it does the same thing if I am between 2600 and 3200 rpms. If I bump to 3500 or over it runs fine, with no cut out or dancing tach (the vast majority of our boating is done between 2800 and 3300rpms).

So first thing this morning I bought a TPS Sensor (throttle Position Sensor). I take the boat to the same friends house (boat runs fine no issues) to install the TPS. So we change the TPS and fire it up it seems to idle fine. Then I run the rpms up a bit and sure enough it is still freakin cutting in and out. So at this point I am out of time and I have to get heading home so I go to fire up my engines and the stupid starboard now will not run , it will only idle for 10-15 seconds and then die. I do this 4 times and at this point I am preparing to putt home on one engine. My steering is on the starboard engine so I fire it one more time so I can steer to get pulled out of the slip and then it is running perfectly fine again. I putt to the end of the cove and take off and the boat runs perfectly fine on my way home.

So what is my ailment?

Changed filter
Replaced TPS sensor


Could it be the fuel pump and it is just starting to crap out and that is why sometimes there is no issue and other times there is?

I appreciate the input,

-Josh

i had the same issues on a 93 502 efi. went on for months until the high pressire fuel pump finaly went out completely.

I'm having a simila problem with mine. 97 31 SS Sonic. 502mag MPI's The starboard engine will shut off from time to time while trying to get on plane. I changed fuel pumps, filters swithed fuel tanks back and forth?? I ran out of good wheather this year to try anything else. so I took it to get winterized. My tech found that the starboard engine was not charging and one of my batt. was stone dead. He thinks this my be the problem. the bad thing is now I will not know untill spring.

I had a similar problem, but at higher speed, tach would bounce all over and engine was weak. Ended up being play in dist shaft screwing up the ignition signal. Was worse when warm.

I have had a similar situation on my 502 MPI, cutting out on one cylinder at around 3000 rpm. It finally went away when I changed the plugwires. My guess is that the ignition componets (Plugs, wires, cap rotor) needs to be in nearly perfect condition for that ignition system to work properly. One weak point in that ignition system is that at around 3000 rpm the ignition advance is at its maximum. At that point the gap between the rotor and the terminals in the distributor is almost 15 mm when the spark is delivered which means that some 40.000 Volts are lost in the distributor. Since the coil only delivers some 50.000 Volts everything needs to be in perfect condition for the system to work around 3000 rpm.

Sounds like an ignition problem either plug/distributor/coil wires (carb or EFI?) or cut out switch out of adjustment on the throttle linkage.

If it were fuel it would be more pronounced, vice quick sputters like you describe. Focus on your ignition wiring vice fuel, air, or compression.

It's efi.

check your cap and rotor. i have seen a lot of these caps pretty crusted up. if that is not it i would get a hold of someone with a ddt scanner before you start throwing parts at. troubleshoot it don't be stupid and waste time and precious money being a parts changer. just so you know mecruiser electrical parts are final sale only. i have seen bad coils that start to breaking up with rpm oh and the ignition module inside the distributor.

That is a good point. Someone mentioned that I could swap the ignition module from the port mill and see if that fixes the problem and then the problem exists on the port. Definately better than burning through parts that I don't need. At this point I have a TPS that I replaced for no reason.

I would start with changing the cap, rotor and plugwires. If that doesn't fix it I would start swapping parts between the engines, coil, ignition module, etc. Your symptoms point to the high tension part of the ignition system