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1985 7.5 dropping a cylinder

C

Capt Fun

New member
Hi All,

I have a real beauty of a 7.5 serial # 6547217 brown stripe that looks new but in the test tank it randomly drops a cylinder at idle and dies. When I say randomly I'm not sure if it's 1 or 2 but it will die. I have the original Merc manual as my folks were a dealer and sold this motor new, I put the Fluke meter on it and everything checks out except the trigger and it appears to have 2 issues. 1- The ohm reading in the manual says 140-160 but the meter shows 135.9 so it is out of range, 2- instead of putting the motor back in the test tank I left it on the stand and hooked the meter back up, shifted into forward and moved the throttle lock to lock to move the harness. I had an ohm change of about 50, does this indicate a broken or failing wire or I'm I barking up the wrong tree? Thank you in advance for any assistance helping me get this running properly and sold to a new owner that can appreciate this gem as I would hate to have to just toss it. Mark
 
That might be the problem. You might try splicing a new wire to the coil as close as possible.

Used ones are out there on E-Bay from time to time.

Jeff
 
The ohm reading in the manual says 140-160 but the meter shows 135.9 so it is out of range​
Click to expand...
This is close enough..the difference could be your meter or meter leads. Forget ohms test and check DVA output. Need to take a timing light and see if its the same cylinder dropping each time...if so its a switchbox. If both it could be stator or trigger
 
Thanks guys, in my post yesterday what I said was not correct, I was getting a 50 ohm variance from the exciter coils not the trigger so I am going with the timing light test and see what shows up. God I hate thinking I'm gonna drop 3 bills on a cd box but if it wasn't such a cream puff I'd deep six it.
 
Problem solved!!!!!!!!!!!!!!!!!!!!!!!!!
Started with the timing light and it was pointing to the top cylinder so I pulled the plug wire off and could hardly hear a crack of fire but the bottom cylinder was snappin like mad so I reversed the wires on both ignition coils and the spark plug wires and it changed cylinders so I started looking for a 339-5288A2 coil. Zip, so I ran across an ignition from a 1976 115 in line 6, it had coils that had the same de mentions but was blue in color and a different part # 339-832757A4 and Sierra said that was a match so I put it in and it runs like new!!!!!!!!!!! Thanks for your help and stay safe!!!! Mark
 
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