1990 Mercury Outboard 135HP Black Max Intermittent No Spark #1 plug

wtwe2step

Seaman Apprentice
Joined
Mar 21, 2008
Messages
36
I hate intermittent problems. 3 times this week, I went out to start the boat and had no spark in the number 1 plug. I go back an hour or so later and it has spark. Its not the plug wire (I switched with another and the problem stayed on #1) and I put a new coil on it to eliminate that possibility (and still had no spark). I check all the wires for bare spots and could not see any. If I start it and take it out for a run without the #1 plug firing it will attempt to fire once in a while but not always. Once it started firing and ran great for 30 mins until I parked it. Today I started it, no spark. Came inside to read forums. Went back out an hour later and turned the key and it had spark. Rode it around for 20 mins with no issues. I turn it off with spark, go out the next morning and no spark ....All the grounds look good.....Arggg .... Is it more likely that the trigger or the switchboxes would have an intermittent issue? or neither? Thanks in advance
 

wtwe2step

Seaman Apprentice
Joined
Mar 21, 2008
Messages
36
Todays Update. When out and started the boat @ 6 am... Sun just coming up, a little cool out...... No Spark .... Let the motor warm up... Turned off and back on ..still no spark..... went back out a 8 ....sun beating on motor .... and yes I have spark...... thinking its temperature related. Something heating up, expanding, and completing a circuit
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,148
That motor has three triggers, so they are shared across cylinders. So probably not a trigger issue. Stator charging coils are shared as well, so probably not stator issue

I would disconnect idle stabilizer, and check switchbox to coil connections. Check #1 coil for cracks.Coils are supposed to have .02 - .04 ohms resistance across the primary and 800 - 100 ohms across the secondary. Check the coil when you have no spark.
 

wtwe2step

Seaman Apprentice
Joined
Mar 21, 2008
Messages
36
Swap Switchboxes and no spark moved from #1 to #2 ........ I've heard you should always replace both as a pair. Thoughts
 

wtwe2step

Seaman Apprentice
Joined
Mar 21, 2008
Messages
36
Thank you for your expert advice. I replaced the switchbox and all is good again. I guess they only last 27 years LOL
 
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