No spark in #3 and #6 cylinders

[86 charger]

I have a 1986 Mercury Black Max XR2 150hp. It has been running rough and coughing and sputtering. I had trouble getting rpm's up to get on plane, so I checked the spark and cylinders #3 and #6 don't have spark. While I was on the water it would surge, kick up and then fall off again. What parts do I need to start to test for replacement or repair? Thanks for your time and help.

 

[achris]

Re: No spark in 2 out of 6 cylinders

Re: No spark in 2 out of 6 cylinders

Spark missing on #2 and #6 is probably a switch box... They are on different triggers, but the same switchbox.... That's where I'd start....

 

[ZigZaggin]

Re: No spark in 2 out of 6 cylinders

Re: No spark in 2 out of 6 cylinders

Agreed. Probably a switchbox. I have a 1985 mercury 90 HP in-line 6 cyl and had a no spark on the #4 cylinder. I purchased a "Seloc online" manual for around $40 and it has more than paid for itself. Very straight forward troubleshooting procedures especially on the ignition. My manual had me troubleshoot the ignition in the following manner: Switchbox, Stator Coil, Trigger Assembly, and Lastly coils. According to Seloc the only way you can test your switchbox is to swap it with a known working one. On the 90 HP each switchbox has 10 wires and sends signal to three coils and each coil fires one cylinder. Thus each switchbox handles 3 cylinders. So I spent the hour and a half or so unhooking 20 wires, physically "flip-flopping" the switchboxes and then re-hooking up all 20 wires. In my case the missing spark did NOT follow the switchbox. Technically, if the switchbox were faulty the #1 cylinder should've been dead after swapping the switchboxes. So after checking the stator and trigger and having them be fine I ultimately found the #4 coil to be dead. Checking the Stator, Trigger, and coils is all done with an ohm meter and testing all three combined took less time than swapping the switchboxes so I would recommend swapping the switchboxes last!

-Zig

 

[achris]

Re: No spark in 2 out of 6 cylinders

Re: No spark in 2 out of 6 cylinders

....According to Seloc the only way you can test your switchbox is to swap it with a known working one. ....

And THAT is precisely why I (and a lot of people on this forum) dislike seloc and clymer... As you found out, swapping switchboxes takes the longest, and they had you doing that first.... Go figure..

My line of troubleshooting always starts with the easiest thing to verify first, not the hardest.... (I'm lazy) The first thing I would have done in your case was just to swap 2 coil leads over... That would have found it quickly and with the LEAST amount of work....

Ok. you can test switchboxes a number of different ways.... Swapping is only one way (and the one that takes the most effort).
You should be putting a DVA meter on the output of the stator (where it connects to the switchbox) and verifying that voltage is available for the box, then you check the trigger voltages, then you check the switchbox output. By now you have a pretty good picture of what's happening in the ignition system, without a single thing being disconnected or swapped...

Chris............

 

[86 charger]

Re: No spark in #3 and #6 cylinders

I posted the wrong cylinder. I do not have spark in #3 or #6, is it still the switch box? Both cylinders are on a different switch box according to the wires. I switched out one of the coils to a cylinder that is getting spark and still no spark on the cylinder. Thanks for your reply, sorry about the wrong information.

 

[achris]

Re: No spark in #3 and #6 cylinders

I posted the wrong cylinder. I do not have spark in #3 or #6, is it still the switch box? Both cylinders are on a different switch box according to the wires. I switched out one of the coils to a cylinder that is getting spark and still no spark on the cylinder. Thanks for your reply, sorry about the wrong information.

That's the trigger... As the firing order is 1-2-3-4-5-6, that puts #3 and #6 opposite. That only can be the trigger...

Look for a loose or broken wire....

Chris........

 

[86 charger]

Re: No spark in #3 and #6 cylinders

Thanks so much for the help, again sorry about the wrong information. Your knowledge is phenomenol and thanks for the diagram, I am a visual learner. I will get the part and try to let you know how it goes.
Nate

 

[achris]

Re: No spark in #3 and #6 cylinders

Thanks so much for the help, again sorry about the wrong information. Your knowledge is phenomenol and thanks for the diagram, I am a visual learner. I will get the part and try to let you know how it goes.
Nate

Me too... That's why I post up so many diagrams.

Chris.........