1994 90hp mercury no spark sporatic

[skey]

Hi all, I have been reading and searching, but just can't seem to get the answers. long read. 1994 90 hp 2 stroke. I have a no spark situation. I have 4 of these motors ranging from 87-94. On the boat is the 94. I have plenty of spare parts. It all started last summer with motor spinning but not running. wait 3 hrs it would crank then run correctly for a couple of hours to a couple of days. then no spark again. I swapped out stator trigger and switch box from a 93 I have. cranked and ran great for 3 outings then no spark. I tested it all again and replaced switch box ran great in yard 1st trip to river it wouldn't leave the dock. I have changed wiring harness. rectifier. coils are good.. It is not a fuel problem. carbs are clean new fuel tank and all lines have been replaced as well as water separator and filters.. Any Ideas??? thanks in advance.

 

[skey]

any ideas

 

[havoc_squad]

The best advice one can give for such intermittent issue is carry the necessary tools and the factory service manual on hand to diagnose the issue.

CDI electronics does carry installation/troubleshooting PDFs available for free that can be used as well.

This is the time/situation where you need to focused on diagnosing the problem. Nothing else will do.

This is assuming a no spark situation.

Go up the chain of faults. Spark gap test -> Ignition Stop Circuit -> Switchbox/Power Pack -> Stator/Flywheel -> Timer Base/Flywheel

The factory service manual or the CDI electronics guide will cover the troubleshooting details.

Personally, I would be concerned about exposed/damaged wires causing open or short circuits with such intermittent issue reported. Open or short circuits can burn up ignition components rather quickly, as the CDI electronics PDF troubleshooting guide warns.

 

[skey]

I have checked and repaired any wire I can find that was questionable. I just went out and it cranked right up and ran for 30 seconds died and cranked back up ran 10 seconds now it wont fire. I dva tested the stator it checks good.

 

[skey]

I will swap out the fly wheel that's a thought.

 

[skey]

I swapped fly wheel it did not change anything.

 

[skey]

what in the wiring harness other than the black and yellow wire that could cause no spark?

 

[skey]

I am still fighting with this. It will crank and run 1 day and not the next. Boat has not moved . would not fire yesterday and cranks right up today. just bump the key and she is running. I have checked wires 10 times wiggle stuff test the wires and wiggle them. I am about ready to make an anchor out of it. But when it is running it runs perfect.??