I am trying to troubleshoot a low hour (around 400h), year 2000 Mercury 200 EFI, SN 0T158142. Compression is good (all between 115 and 120 psi). Fuel components are good (new fuel line, new in-line racor, new fuel filter, clean fuel pump screen, good fuel pressure, etc.) The only major component that has not been cleaned/serviced are the injectors. When the motor runs, it runs great. Starts quickly, idles well, jumps on plane, and reaches rated RPM (around 6K when lightly loaded).
A little back ground:
Last year, on my way to the Bahamas, I stopped to take a break and eat a snack. Prior to this I was cruising at about 4500rpm for about 2 hours. Pulled back the throttle, and let it idle forward while I ate a sandwich and had a drink. When I tried to throttle up, the motor would not get past about 1500 RPM and was shaking badly. I shut it off, restarted and tried again with same results. The motor would start, but idled poorly and would not throttle up. I tried pumping the fuel bulb and that made no difference. I changed the Racor filter/separator and the internal fuel filter - and that made no difference. Since the motor was still running and I was still in the middle of the ocean, I put it in gear and idled the rest of the way to Bimini Bahamas.
The only other issue that could be related, is that I had an low oil alarm during this voyage. The oil tank on top of the motor was not filling as fast as the oil was being consumed, but it was at worst low enough to trigger the alarm when I hit a wave just right. That issue was later diagnosed and fixed - it was a cracked oil cap. As a precaution, I am about to pull the oil injection entirely and go to pre-mix.
When I arrived in Bimini, one of the locals saw me trying to fix the motor and came to help. Unfortunately, we were not very systematic in our attempts and messed with everything. We unplugged a bunch of stuff, messed with timing, messed with idle, etc. From my recollection, when running poorly the motor was running on 3 cylinders (no ignition).
At some point, we the problem became intermittent. The motor would run fine only to bog on the next run. We then realized that shutting the motor off all the way (key all the way off) would almost always result in the motor running fine for a short time. After wiggling more stuff - the problem went away and has only reappeared once since. A quick shut down and re-start fixed it.
Now:
I am about to service the boat for this season. I would like to regain confidence in the motor, so I can take it off-shore. It seems that with the older motors it was always the stator or switch box. Because I don't have much free time to "mess" with the boat, on top of the yearly plugs and filters I was going to throw some parts at it. I was thinking a stator, trigger, and regulators. After a bit of reading, it appears that this generation of EFI is more complicated with more moving parts. Now I am not sure what to do, and could use some guidance. I have the manual, and a multi-meter, hand tools, and general mechanical/electrical knowledge. Please help me fix this so I can enjoy the boat again instead of stressing out!
Mike