Cross firing Mercury Black Max V-6

[coffeeguy]

Chasing a gremlin on a friend's boat that won't rev.
Do faulity switch boxes cause cross firing?`
I indexed the cylinders and using the timing gun can see 2 cylinders firing at the same time.
First set of boxes were the cheap FleaBay ones. I can see markings 1&3,2&4,3&5,4&6 ect firing at the same time.
I swapped out those for his originals and the idle picked up from 650 to 1000 .
1,3&5 all showed only the correct cylinder firing but 2,4&6 were showing pairs going off at the same time.
Tried a set of boxes that were laying around and idle went higher(1400) but could see faint double firing going on on all cylinders(much harder to read the wrong cylinder that was firing but could still see something)

[coffeeguy]

It does have a new stator that checks out fine on the ohm meter test

[Mrzip]

Two New Switch Box's .

[skialot2]

Yes. Switch boxes can cause all kinds of crazy things. I find used OEM from eBay to be better than cheap knock offs.

[pcrussell50]

Yes. Switch boxes can cause all kinds of crazy things. I find used OEM from eBay to be better than cheap knock offs.

I have two sets of OEM switch boxes on my two V6es, a 2.0/150 and 2.4/200. AFAICT they are actually from the mid-‘80’s when the motors were built. But they seem to run nicely.

Others on here have given good reports the Sierra switch boxes that are made in Germany. But of course they aren’t cheap, either. You could buy four pairs of ebayZon Chineseium boxes for the cost of just a single German Sierra box. My 2.4 came with those, but I chose to use a set of OEMs I had lying about. Based on positive reports from other S&F’ers I wouldn’t be afraid to try my Sierras if the need arose.

-Peter

[Baker343]

Definitely not a expert on testing electronics but I would have tried swapping wires from the switch boxes to see if the problem switched sides. Check all of your grounds really good

[Mrzip]

.... CDI.. Electrical has aways been good for me..