Logo
FULL SITE MENU

No spark bottom cylinder an 35hp Mercury

D

daswen

New member
I lost spark to the bottom cyl

I lost spark to the bottom cylinder when I was at 3/4 throttle. Is it likely the coil or another part. It is a 1986 or 87 engine.
 
"swap coils side to side,
th

"swap coils side to side,
this site has troubleshooting section(download) and resistance/dva chart for testing
I'm guessing the switchbox
http://cdielectronics.com/Downloads/tabid/55/language/en-US/Default.aspx"
 
Thanks JB.
I'll try switc

Thanks JB.
I'll try switching the coils next week. I see swithboxes are a lot less expensive on this site.
 
I switched the coils and still

I switched the coils and still no spark on the bottom cylinder. Top cylinder still had spark. Should I try a new switchbox?
 
"yes, if the wiring from the s

"yes, if the wiring from the switchbox to the coil is good and the trigger passes its resistance test(ohms test). Page 67 of the above link
NO SPARK OR INTERMITTENT ON ONE CYLINDER:
1. Check the DVA output on the green wires from the switch box while connected to the ignition coils. Check the reading on
the switch box terminal AND on the ignition coil terminal. You should have a reading of at least 150V or more at both
places. If the reading is low on one cylinder, disconnect the green wire from the ignition coil for that cylinder and reconnect
it to a load resistor. Retest. If the reading is now good, the ignition coil is likely bad. A continued low reading indicates a
bad switch box.
2. Check the trigger resistance and DVA output as shown below:
Wire Color Check To (Wire Color) Resistance DVA Reading
Brown wire White wire 800-1400 4V or more Connected
Brown wire Engine GND Open 1V or more (*)
White wire Engine GND Open 1V or more (*)
(*) This reading can be used to determine if a pack has a problem in the triggering circuit. For instance, if you have no fire on
one cylinder and the DVA trigger reading for that cylinder is low – disconnect the trigger wire and recheck the DVA output
to ground from the trigger wire. If the reading stays low – the trigger is bad.
3. Connect a inductive tach to each cylinder and compare the RPM readings at the RPM where the problem is occurring. If
only one cylinder is dropping out, swap the ignition coil locations and retest. If the problem follows a coil, replace the coil.
If it stays on the same spark plug, replace the switch box.
4. Check the flywheel magnets to see if one has come loose and moved."
 
"Wow, that was a very long, im

"Wow, that was a very long, impressive post there Dad - you are starting to sound like me
"
 
Thanks JB. I'll pull the f

Thanks JB. I'll pull the flywheel and check the magnets. I don't have a meter to do the other tests. If the magnets are okay I'll order a switchbox and try that.

Thanks again.
 
"Hello. I am having the same

"Hello. I am having the same issue. Boat was running fine and I lost spark to bottom cylinder. Thinking it may be the coil or switch box? Did you finally solve your issue? If so, could you share what fixed it? Thanks."
 
"After letting sit overnight I

"After letting sit overnight I went out and to my surprise it started right up on both cylinders. I started and stopped and few times and everything seemed fine. I let run for approximately 5 mins, stopped and then tried to restart and it went back to only running on the top cylinder? I don't have the tools to pop the flywheel. Still the switch box? Thanks."
 
Definitely the switchbox. I ha

Definitely the switchbox. I had one do that exact same thing to me.

There's a used one on eBay at the moment.

Jeff
 
I have not gotten back to my c

I have not gotten back to my camp yet to work on the engine and check the magnets. Mine sat for a couple of weeks and it still had no spark on the bottom cylinder. I think I might just buy a switch box and put it on. It looks very easy to change.
I should get to work on it within a couple of weeks. I'll update as to what happens.
 
I checked the magnets yesterda

I checked the magnets yesterday. I was able to feel up underneath the flywheel. I was able to push hard on the magnets and they did not move. I rotated the flywheel to check each of the magnets. I just ordered a switch box and hope to put it on over the 4th of July.
 
Looks like it was the switch b

Looks like it was the switch box. Was able to water test yesterday and everything seems fine. Thanks for your help.
 
Back
Top