Inconsistent Sparks

[manymerrymoods]

Hi all-

Working on my 1985 Mercruiser 3.7 170 HP.

We are getting inconsistent sparks out of the distributor. Currently, there is a spark coming from the cap for cylinders 2, 3, and 4. When all four wires are attached, there is no spark for 1. But, when the other three wires are removed, we do have a spark coming out of cylinder 1.

For reference, put in a brand new: coil, distributor (including cam, cap, rotor, points, etc.), sparks, wires, and confirmed the point gap is accurate.

Any idea of why we don't have consistent sparks for all four cylinders or what to do next to troubleshoot? Really appreciate your help!!

 

[nola mike]

Hi all-

Working on my 1985 Mercruiser 3.7 170 HP.

We are getting inconsistent sparks out of the distributor. Currently, there is a spark coming from the cap for cylinders 2, 3, and 4. When all four wires are attached, there is no spark for 1. But, when the other three wires are removed, we do have a spark coming out of cylinder 1.

For reference, put in a brand new: coil, distributor (including cam, cap, rotor, points, etc.), sparks, wires, and confirmed the point gap is accurate.

Any idea of why we don't have consistent sparks for all four cylinders or what to do next to troubleshoot? Really appreciate your help!!

Did you set dwell also? Are you getting a nice blue spark on the working cylinders or is it yellow/weak? If you're getting a good spark from the coil and not from 1 cylinder, it's either the wire, cap, or rotor.

 

[kenny nunez]

Get a jumper wire and connect the + side of the coil to a 12 volt source and check the spark while spinning the engine. You may have a problem with the starter boost solenoid By-pass circuit which delivers 12 volts in cranking mode only.
Does the rotor shaft have enough movement to make the points open more than the measured gap?

 

[manymerrymoods]

Did you set dwell also? Are you getting a nice blue spark on the working cylinders or is it yellow/weak? If you're getting a good spark from the coil and not from 1 cylinder, it's either the wire, cap, or rotor.

Set the dwell as well. Just replaced rotor, wire, and cap (again) and am getting spark to all four cylinders. Thank you so much for your help!!