84 mercury 90 HP 6cyl intermittent fire

[Ranger520vx]

Helping a friend with his motor some cylinders are firing some aren't sometimes they will fire then stop. He put a new stator on a year ago it is the black one. Have checked all the coils and wires and they are all good. Going to get a shop manual for it so we can check the stator and trigger. Just thought maybe someone had some ideas .

[fishinwrench]

Momentarily disconnect the two yellow wires from the voltage rectifier/regulator and see if that restores consistent spark to all cylinders. 

You won't be able to test the stator, switch box, and trigger output unless you have access to a DVA meter to measure pulse voltage.  The resistance (ohms) tests are misleading and a waste of time unless you are comparing the integrity of two or more of the same components.

You can use a timing light to determine which cylinders are loosing fire.  If the ones loosing fire are on the same switch box .....then Shazam! you found the problem. 

[Ranger520vx]

I forgot to say we unhooked the rectifier and didn't change anything. The misfiring cylinders are on both switch boxes

 

[Ranger520vx]

We have a digital and swing arm multi meters. Yesterday we had 2 cylinders not firing then 1 started firing today have 3 not firing using timing light. I'm a diesel mechanic by trade but don't do a lot of outboard work any help would be appreciated Wrench thanks

[fishinwrench]

[Ranger520vx]

Thanks wrench stator ohms out according to that page voltage also is good on stator while cranking. #1 and 3 are only cylinders firing. Trigger ohms are in spec. and has 5 volts coming in on all trigger wires. But if you check them going to ground you have to put the positive to ground and groung lead on the wire at the switch box. But have no voltage at any of the green wires coming out of the switch box going to the coils.

[fishinwrench]

You should have voltage coming out of the green primary wires on the cylinders that ARE firing.  Again though, you are testing pulse voltage that requires a peak reading adapter (DVA).   

When I test ignition systems I pay no attention to resistance tests, I'm only concerned with output.

I only go by resistance testing if I'm bench testing something, and even then it is unreliable.

[Ranger520vx]

OK thanks I will see about getting a DVA and check it out. Figured I would have to come up with one since I wasn't getting any voltage out of the primary wires on the cylinders that were firing. I really appreciate all the help.

[fishinwrench]

If you really feel creative.....

 

[Ranger520vx]

Hey thanks that's pretty cool but I found one on eBay for $19 think I will just order it. When it gets here then I can run through all the tests and figure out what we have.