99 Mercury 225 EFI running bad

[KemahBTR]

My 1999 Mercury 225 EFI with 50 hours on it, started running bad after sitting for 4 weeks. The engine will start right up and idle no problem (little ruff though). When I put the throttle down it just slowly crawls to about 3000 rpm and it will not go any faster. Sometimes it won't go above 2000 rpm and it sounds like it is on it's last leg. I replaced the plugs and noticed that one of them is not firing, but one plug shouldn't cause this much trouble. I looked at the rest of the plugs after running it for a while and they were wet, like they're not firing enough or something. Any suggestions on what might be wrong????

 

[Waterbugtoo]

Re: 99 Mercury 225 EFI running bad

Take it to a dealer and put a tester on it or else it will be trial and error and probably not finding the problem. EFI is not really a DIY friendly motor. If it happens to be the computer and you keep running it, it could really screw up your powerhead.

 

[12Footer]

Re: 99 Mercury 225 EFI running bad

If one plug is not firing, take it to the dock. Just in the chance that is is fuel-related, and that cylinder is getting zero fuel....Zero fuel= zero oil...Bad news.<br />EFI, as Waterbugtoo says, is not easy to diagnose in the back yard, in many cases.<br />But you can do the following before giving it to the wrench;<br /><br />Take compression readings.Check filters.<br /><br />check the entire fuel system for air leaks, primer ball collapsing, loose bolts on the fuel pump, fuel pump getting power, clean contacts shiny on computer contacts,and inspect the plug wires for shiny contacts. run the engine on a dark night, and look for visable arcing.<br />After this, it's time to get some help from "Freddy Mercury man".<br />The injectors are expensive, making switch-out risky to the wallet.<br />My gut guess is this is the problem (plugged injector).