RPMs increase when drive trim button pressed
 

Twin engine 502 MPI with MEFI1. Had the boat out for the first time yesterday and having an issue.

Starts and idles great and fuel pressure is good. I get on plane and notice the port engine is at 3000 rpms and the starboard is only 2400. I was thinking that drive may be tucked in further so I hit the trim switch. Immediately the rpm picks up 4--500. I let off the switch and rpms drops 4-500. Did this 5 or 6 times and every time the rpms immediately picks up. Doesn't matter if I trim up or down. I did give it more throttle and no misses, pops or funny noises. Just sounds "sluggish".

I was thinking a bad ground that is somehow being closed when I hit the trim button. But I have cleaned and check all grounds. I also double checked base timing and verified timing is advancing at higher rpms on the hose.

I did read that if my knock sensor wire is too close to a spark plug wire it could interfere with the knock sensor and pull timing. So I am going to double check that.

Next plan is to take the laptop when I run it again, and see what the timing and knock retard is doing under load. But open to any ideas that I can try next time I am on the water.

I will add that it almost felt like it was in "limp mode". But oil pressure, water temp and drive lube are all okay and no alarms.

I would say ground issue. My boat did the same thing but it would happen after it had warmed up and run about 20 miles. I added more grounds to the motor and checked all the grounds on the switches. Whatever I touched, added, or put back together fixed it.

Thanks for the reply. Google search was getting me nowhere so glad to know I'm not the only one! I will double check the grounds at the switches as well.

When you say you added more grounds. Are you talking engine to battery?

Yes, I added 2 more ground wires to the motor and battery. Under the dash I found some previously hacked up wiring that I corrected and cleaned all my connections. Like I said I don't know which of these items fixed it but its fixed and adding a couple of wires to ground the motor better wasn't difficult. Now looking at crappy wiring that had been paid to be done properly pissed me off. Another reason to do your own work, its seems I always have to go behind everyone and fix it anyway.