350 Mercruiser intermittently losing power

[jrogers]

I have a 2001 22i with a 350 Mercruiser. I'm experiencing an intermittent issue where the RPM's will drop off. The history goes something like this:

Day 1: Running the boat pulling people on wakeboards for 90 minutes. Cruising back at 3000 rpm and the power dropped to 2800 rpm five or six times for a a couple of seconds. Didn't touch the throttle and it recovered. It didn't do it again the rest of the day.

Day 2: Running the boat to get gas in the morning at around 3200 rpm. The power drops to 2200 rpm and recovers with no change in throttle; drops to 2700 rpm I back off on the throttle but power continues to fall so I give it full throttle and it picks back up; a few seconds later the same problem occurs. After doing this for 60 to 90 seconds the problem seemed to resolve itself. While getting gas I pull and drain the fuel filter. No apparent water and no serious contamination. Start the boat after filling up and run it in neutral at 3000 rpm for a few minutes. Power fades occasionally but the problem goes away after a minute or two.

Day 3: Pulling wakeboards for about an hour. Power begins to fade again and eventually the motor backfires and dies after about a minute of power loss and recovery. Motor does not restart. Checked the coil and it was sparking. Wait 5 minutes and boat restarts. We use the boat the rest of the day without incident.

All plug wires appear to be making good contact. I have not had a chance to pull the plugs yet but will do next weekend

In reading other threads (I love the forum!) it sounds like this could be symptomatic of an ignition sensor but I don't know if they tend to fail intermittently like this. Anyone had a similar problem or any advice on troubleshooting this?

[30521v]

I am having similar problems, although much worse.

Another member "ruger" advised me to check these, maybe it will help you out

Id begin prob checking fuel pressure or making sure your fuel pump is at least still coming on. Do you know if they changed the fuel filters? If not, need to do that. Check and see how the distributer cap looks along with the rotor. Bet its wore pretty good depending on how many hours are on the boat same with spark plugs and wires. One other thing make sure hitting the roller didnt somehow knock a sensor wire off.

[jrogers]

Thanks for the information 30521v. I read your thread, sorry to hear you are having so many issues.

[boatwakes]

Jrogers, that engine should have the ignition sensor replace if it hasn't been done yet anyway. If it's been replaced, there will be a white with red striped wire, a white with green striped wire and a solid black wire coming out of the bottom of the distributor. If it has not, you will not have the solid black. Your problem actually sounds like the TPS (throttle position sensor) Mercruiser part# 853678T ($90) but others on here have found them at auto zone for a 1998 MPI chevy. After you check the fuel pressure, let us know what you find with the spark checker.

[AmandaReed]

I relate some of this problem. It sounds like; maybe you have some growth on the bottom, or engine needs tune up. Take compression test to be sure engine is not sick.
Marine Engine Parts

[jrogers]

Checked the fuel pressure using the shrader valve on the fuel rail and it was only reading 30 psi. Based on some research it looks like the fuel pressure should be more like 43 psi so this might be my problem. I've never changed a fuel pump before, how difficult is it to do on the 350 mpi?

Also, Boatwakes, checked the ignition sensor and I do have a newer one. Thanks for pointing the wire color out, I never would have found that thing if I wasn't able to trace the wires.