225 EFI dropped rpms?

[rchunt]

S/N is OT666429. 2003 225 EFI Merc. I bought the boat and motor about 4 months ago and it has ran flawlessly until saturday. It started being sluggish out of the hole and it will only turn 4500 rpms wot. It cranks and runs, idles fine, no misses. A little history, when I bought the boat I had a diagnostic ran and only had 175hrs. The only error code was from one of the coils and it just happened one time. It was a couple of months before I purchased it. I didn't really think anything about it since it ran so good and the compression was 110 on each cylinder. Back to saturday. So, I checked the compression again this weekend after the trouble and it is still 110 on each. Could the coil have finally gone bad? Could it be a bad plug because I don't think the plugs are that recent?

[EuropeanAM]

You've checked the compression--- good idea to continue and check the OTHER basics:

-Spark Test (and confirm good, clean Champion QL77CC spark plugs)
-Fuel Quality, Delivery, and Fuel Pressure Tests.

Be glad to help further (if necessary)....

[rchunt]

I put a new set of Champion QL77CC in yesterday and still have the problem. How could I check the coils to see if they are good without the diagnostic equipment?

[Johns46470]

Check your fuel line mine was coming apart on the inside and clogged the fuel screen. Same symptoms you are having, it ran great until you tried to give it more fuel.

[EuropeanAM]

I put a new set of Champion QL77CC in yesterday and still have the problem. How could I check the coils to see if they are good without the diagnostic equipment?

An inductive pickup timing light works well.... clip it to one plug wire at a time (while watching the light pattern).

Also check:

http://www.bbcboards.net/mercury-3-l...tem-first.html

[rchunt]

I have all new fuel lines. The previous owner had them installed. I don't have access to a light. I was told that while the motor is running I could unplug the wired connector side of the coil one at a time I could detect a bad coil by listening for the one that has no change in the motor running.

[EuropeanAM]

You can try that.... but it's very difficult to ascertain one cylinder dropping (at idle) on this engine model.

A gap-style spark tester can also be utilized, if you don't have access to a timing light.