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90HP V4 E90TLESB no spark on one or two cylinders

J

johnnyclear

New member
I bought a boat with this motor a few weeks ago. Installed new plugs. The old plugs didn't look really bad to my inexperienced eyes.
Checked compression today: (looking aft to fore) Top Left 122, Bot Left 120, Top Right 120, Bot Right 125
Three month-old plugs looked a little bit used, black and oily. Bottom right looked brand new, unused.

Pulled plugs on right side and laid metal exterior on bare bolt on engine. Top has spark. Bottom no spark. Switched plugs, then cables.
Same story: top cylinder has spark, bottom no.

Reinstall plugs and wires. Motor starts and runs. We had been using it like this quite a bit recently.

Switched coils on top and bottom right side. Reattached with just one bolt each. (wire from power pack is not long enough to just switch wires from power pack and then plug wires) Now I get spark on *neither* top nor bottom right side. Wiggled wires and rechecked. Switched plugs. No change. There is no spark on either top or bottom right side, when checking visually with pulled plug. Fit one plug into boot on good left top cylinder just to see if I am hallucinating. I do see a good spark there as expected.

Start engine. It runs, but fast idle has to be a bit high. Pulled wires from top right, hear no difference. Pull wires from both top right and bottom right, hear no difference in running engine.

So now... ?

Should I swap the coils back to the original position and verify that I get spark on three cylinders again (if possible) ?

Then maybe swap a coil from left to right?

Is it possible that something in the power pack damaged bottom right coil and when I swapped it with the top right coil, the second coil was damaged, too? I am reluctant to swap in a third coil on the original bad cylinder.
 
I took too long re-editing, so it would not save. But I forgot to add a detail:

After swapping the top right and bottom right coils as described above, I did this:
Start engine it runs about the same as before. I am thinking that the bottom right is now working and top right is not. But I stop the engine and pull plugs on right side. There is smoke coming out of the top right cylinder. None coming out of bottom.

Then, as I described above, I did this:
Check spark visually as above. I get spark on *neither* top nor bottom right side. Wiggled wires and rechecked. Switched plugs. No change. There is no spark on either top or bottom right side, when checking visually with pulled plug. Fit one plug into boot on good left top cylinder just to see if I am hallucinating. I do see a good spark there as expected.
 
Wait... I just noticed that only one bolt on the coils pushes the grounded plate to the block.

I only put in one bolt, the wrong one. I'll retry now.
 
It was indeed bad contact due to not fastening the bolt on the conducting plate. Now when I swap coils between the no-spark cylinder and the good cylinder, the spark goes with them. Engine runs a it better now that there are three cylinders firing.

It seems clear that buying a new coil is the thing to do.
 
Just to finish the story. I replaced the bad coil. I guess the cylinder has spark now. The engine runs far better. Before, I could not get more than 4200 rpm before on the water. Now I easily reach 5500 rpm before full throttle.
 
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