Intermittent/ no spark on cylinder 2, inline 6

[1979checkmate]

Okay, 1979 115 hp mercury inline 6. Cd distributorless ignition. I seam to have a no spark/ intermittent spark issue on cylinder 2. A little more background: i have replaced the stator and trigger with new CDI parts. One switchbox was bad so i replaced it with a working used one. I switched around cylinder 1 and cylinder 2 coils and the problem does not seam to follow the coil or spark plug wire. Cylinder 2 seams to be the only cylinder not firing. I hooked up and inductive timing light to cylinder 2 and ran the motor, the light does go off indicating a spark once in a while, but not nearly as often as it should. ANybody have any idea what could be the problem?

 

[daveswaves]

Re: Intermittent/ no spark on cylinder 2, inline 6

If it does not follow the coil, wire , or plug it could be a poor ground at the #2 coil location. Run the engine at night if you can and look for spark leakage. There is a possibility that the bias circuit on the switchbox you did not change is bad. If so it could still be used on a 3 cyl but not on a 6.

 

[1979checkmate]

Re: Intermittent/ no spark on cylinder 2, inline 6

Thanks,
Could i flip flop the two switchboxes and see if the miss changes cylinder as a test?

 

[Faztbullet]

Re: Intermittent/ no spark on cylinder 2, inline 6

Yep and test the trigger also ....

 

[daveswaves]

Re: Intermittent/ no spark on cylinder 2, inline 6

Yep and test the trigger also ....

Exactamundo

 

[1979checkmate]

Re: Intermittent/ no spark on cylinder 2, inline 6

trigger is brand new CDI, but that doesnt mean it couldnt be bad... but doesnt each coil on the trigger control 2 cylinders?

 

[daveswaves]

Re: Intermittent/ no spark on cylinder 2, inline 6

trigger is brand new CDI, but that doesnt mean it couldnt be bad... but doesnt each coil on the trigger control 2 cylinders?

Yes, and your cdi trigger is probably ok, however, if you swap the switch boxes and it stays at 2 the trigger is "suspect". More likely it is a switch box with a faulty bias circuit. That condition can take out the other switch box and sometimes the trigger. That sounds like what happened originally. You replaced the blown switchbox leaving the one with a potential bias circuit problem in place. Thats why Merc recommends changing both switch boxes. Flakey spark on one cyl is usually the coil, the wire, the plug, poor ground, or a faulty bias circuit. Faulty bias circuit can take out the "other" switch box and sometimes the trigger. Fun eh?

 

[Faztbullet]

Re: Intermittent/ no spark on cylinder 2, inline 6

trigger is brand new CDI, but that doesnt mean it couldnt be bad

Have had several this year....

 

[1979checkmate]

Re: Intermittent/ no spark on cylinder 2, inline 6

will it take the switchbox a while to screw up the other box and trigger? I just dont want to ruin the good switchbox and trigger while i am testing and troubleshooting

 

[daveswaves]

Re: Intermittent/ no spark on cylinder 2, inline 6

you will be cranking it not starting it, the short period of time that you will be testing will not hurt the good switchbox or the trigger, voltages will be nominal and your cranking speed at best will be 300 rpm. Swap the boxes and see what happens to number 2.

 

[Laddies]

Re: Intermittent/ no spark on cylinder 2, inline 6

A faulty trigger will effect 2 cyls. 1 cyl. must be a coil,related wiring or a box!