Logo
FULL SITE MENU

Lost power when changed plugs

B

bbcampbell

New member
I just changed the spark plugs on my 2004 Mercury 225 Optimax. It was running okay, but the plugs had never been changed before, just checked, but I had a new set (NGK, identical to original ones), so I changed them. Nothing else was done at this time.
When I launched the boat, to drive it over, to be returned to my dock's boat lift, it would only attain 57 mph!
This engine is on a 2005 Triton TR 21 X-DC bass boat. Previously, with just me on board, it would always run 69-70 mph, depending how much fuel was on board.
Any suggestions, or answers would certainly be appreciated!
Thanks!
Bob
 
Change back to your old plugs and see if the speed comes back.

What was the MAX RPM reached with the new plugs and with the old plugs?

How did you gap the new plugs?
 
I must admit, I did not note the RPMs. My owner's manual says the gap should be .031". I do not have a .031" gap gauge, so used a .030", and made it a "loose fit", but touching.
The plugs are NGK. Same number as original. Pretty pricey. I was careful to reconnect each wire connector, so they would have good contact. Maybe I should recheck this first?
I do still have the old plugs. They really looked pretty good, especially for their age.
It seems like probably only 1 plug is not firing. Not sure how to confirm which one?
thanks!
Bob
 
Last edited:
you could put an inductive timing light on each plug one at a time is one way...you could also use a gap test to see if you see a difference or absence of fire on one cylinder..you could also pull the plugs shortly and see if you can see any difference in one of them...color...wetness...etc...

do you think one cylinder is failing to fire or intermittent at all speeds?
 
I guess I need to try & find some sort of video tutorial, or at least a schematic, since I couldn't identify the directors, nor direct injectors. But I am curious how they could have gotten unplugged?
 
Back
Top