Merc 250 efi only firing on 5 cylinders
looking for a little help on one of my 1998 merc 250 efi’s. I have a pair of them on the back of my boat one runs great the other is running a bit rough.
Went to do some yearly maintenance, pulled the plugs(champion ql77cc) and found that number 6 cylinder, bottom left was all gummed up and had fresh fuel on it. Turns out it’s not firing after a spark test, I’m getting only 5. The bottom left is the one not firing.
I got a new coil, checked all the grounds, ohm’Ed out the crank position sensor, ohm’ed all the rest of the coil’s, omh’ed out the stator bobbins, checked continuity on the grounds, stater wire, trigger wire, stop wire, swapped the ecm ignition module with the other motor and nothing. Did a compression test and all came it at 115psi.
This one has me stumped, any suggestions? I went through the service manual and performed all the tests under 2A ignition troubleshooting and haven’t been able to find the culprit.
Any suggestions or help would be much appreciated!