2005 Mercury 200hp efi...

[jb3601]

I bought a 2005 Triton in Sept. It has a 2005 Mercury 200hp EFI 3.0. It has started fouling the plugs the last two times I've run it. Had a guy look at it and he couldn't find anything Mechanical wrong w it. Compression was good, fuel pressure is good. He says it would run good for a while and then it would start missing on a couple of cyls. He'd kill it and restart it and it would run fine. Let it run a while and it'd start running rough again. Does this sound like the ECM is going bad? Thanks for any info.

[JOE54]

sound like fuel delivery problem (injectors)possibly

[Savage]

I doubt the ECM (PCM) is the problem.

[EuropeanAM]

If you would, please take a moment to review the Announcements at the top of the Forum, and be sure to provide the Required Info (serial number) when posting. Thanks!

I too expect it to be fuel or ignition related- either losing spark due to coil/wire/plug that is malfunctioning, OR losing fuel (which can be, and often is a shorted wire inside the Air Attenuator, where the injector harness passes through it's retaining clips).

[jb3601]

Thanks for all the info. The dealer I bought it from is going to check it out next Tuesday.

[jb3601]

Well... made the trip to the dealer this morning. They checked it out and found a couple of things wrong. The lift pump diaphragm was leaking so they rebuilt it. Put a new set of plugs in it and fired it up. Starboard side thermostat was not closing and would only get up to 75 deg on that side. Port side was only 110-112 deg. They changed t-stat out and starboard side went up to 133 deg. Port side was still around 110-112. Only had one t-stat in stock so they are shipping me one when they come in and I'll change it out myself. They said with the engine not getting up to operating temp it was telling computer that it needed more fuel and it was continually dumping raw fuel into cyls. Motor idles and sounds like a complete different motor.

[Champ 2001]

Good to hear that you got it figured out!

[EuropeanAM]

Amazing how much happier they are at operating temp.