1986 Merc 90 "Tower" bad unpredictable spark

Here is a pretty sweet ride. I originally had no spark on two cylinders switched final spark coil and it did not follow. Therefore decided to replace stator, trigger, and both switch boxes, since this was all original and of course 36 years old. Ordered CDI Electronics units from Marine Engine with delivery in only 2 days.....very exceptional. Now we have only intermittent spark on four cylinders, coming in very unpredictable pattern. The spark that does come is very strong with almost one half inch arc. What did I do wrong? New switch boxes are properly grounded and all wiring is precise and correct. Everything went together perfectly. Did I make a mistake by ordering CDI Electronics equipment? Thanks, Tim.

Here is a couple more photos.

C'mon.....you techs.....nobody gonna help me get this Peterbilt on the water? Talk to myself alot these days.....at least one person will listen to me.

Which 2 cylinders are not firing? Possibly ignition coil issues, spark plug wires? You really need a DVA (Direct Voltage Adapter) in order to read the voltage at the ignition coils, switch box, and stator. The DVA is a must-have tool to have, and a money maker at my shop!

I originally had no spark on two cylinders switched final spark coil and it did not follow.

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Which two? Which four are intermittent? Likely a POS trigger as CDI quality control has been lacking for several years..

Sorry...I don't remember....I was so mad, I took my tools and went home. Don't think I'm ever using CDI again. I have a DVA meter, yes...use it alot. This guy owns a very successful trucking company.....seems I just made a fool of myself.

Wanted to prove myself a fool. CDI products proved perfect. Finally got back to the Peterbilt. Started checking with multimeter. Trigger fine, stator fine....but....poor ground connection to stator. I had somehow gone to black/white @ switch boxes. As some of you may know, you have to create a new ground for CDI composite case switch boxes. I had somehow placed stator ground, solid black, on the "black/white" jumper between boxes. Stupid. Luckily didn't "toast" anything as I tested spark late that night. Starting to "slip up" occasionally now. Got to do with vision, perhaps.....not sure. Gotta double and triple check when not using OEM parts especially.

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Pretty neat "Pete".
Power provided by vintage Merc "Tower".

There's supposed to be a wire that goes from one switch box to the other. Did you leave it out?

Jeff

No, that was in there. You know it's white/black. The packs are not oriented the same. The lower one goes upside down, so to speak. I had stator ground going to the white black. I'm getting careless. It was getting late, and the owner wanted to close up for the night. I was working on it at his lake home.....poor lighting, after dark, and different grounds on the switch boxes from OEM. Probably gonna have to hang up the wrenches in a few years and have a big auction. Almost screwed up the job.
Jeff does 50 million dollars revenue per year with over 250 employed. He started trucking in 1981, then slowly built up his fleet. The pontoon was a retired 86 Peterbilt and Jeff put the body shell on a junk pontoon boat after adding a center pontoon. The Merc was the original power on the pontoon in 1986 compression is 125 to 120 psi.
Picture is looking out from the port side drive adjustable air ride chairs.