Mercury coil problem ??

[entsminger]

I'm new to this forum so please bare with me.

I have a small 7.5 Mercury outboard motor that is at least 30 years old. It has run great forever but in the last few years one spark plug or the other has stopped firing. I took it to the shop twice and each time they said they fixed it and or replaced a coil that was bad. Last time out one plug stopped firing again 5 miles down river, aahhhh!! and I'm wondering if something else could be causing this problem. I've put in new plugs and all the wiring seems fine. I have my doubts as to whether the shop actually replaced the coils at all as they look like they were never removed?? Is there some way to test the coils to see if they are bad coils or could something else cause a plug to not fire?

Thanks

Scott sdakss@aol.com

 

[turtles11756]

Re: Mercury coil problem ??

post serial # that will tell the year made .does it have points in ignition ? check all the wiring needs to have a hot spark ? get a spark tester . i have a 1969' 7.5hp it had no spark put in new coils $45.00 each and new ignition points (two sets) and the slightist film on the points had it firing on only one cylinder. the coils can be tested easily

 

[entsminger]

Re: Mercury coil problem ??

Thanks, I'll try and find the serial number. The guy at the shop said new coils couldn't be found? I'm just guessing that this engine doesn't have points but I'll see if I can find out. What would a spark test do that watching the pulled spark plug wouldn't or does it test the coil somehow?

Scott

 

[Deep V]

Re: Mercury coil problem ??

Scott, I'm no expert, but I had the same problem with my '78 Mariner. I replaced the secondary coil on that cylinder,assuming that was the problem, because it had a tiny crack in the casing. It didn't fix it. The problem ended-up being in the wiring harness (or lead wires).Corroded wires make contact sometimes, sometimes they don't. Good luck, Rick.

 

[entsminger]

Re: Mercury coil problem ??

One thing I noticed was that at times the engine would run on both cylinders and then for a few minutes one would quit and then suddenly both would work again for a few minutes back and forth but eventually one would quit all together. I'm thinking that would tend to indicate it wasn't a bad coil but rather something else? It never seemed to have this problem early in the trip but rather miles out and on the way back?? The engine would run great early on we'd go way out and then one cylinder would always quit later in the day.

Thanks
Scott

 

[entsminger]

Re: Mercury coil problem ??

The serial number is 8804295 and it says the motor is a Comet Lightning on the side of the engine and the only other number I see on the engine is 8375284.

Thanks
Scott

 

[entsminger]

Re: Mercury coil problem ??

Hey, can anyone help me here , I got the serial numbers ?

Scott

 

[CDI Tech Support]

Re: Mercury coil problem ??

One thing I noticed was that at times the engine would run on both cylinders and then for a few minutes one would quit and then suddenly both would work again for a few minutes back and forth but eventually one would quit all together. I'm thinking that would tend to indicate it wasn't a bad coil but rather something else? It never seemed to have this problem early in the trip but rather miles out and on the way back?? The engine would run great early on we'd go way out and then one cylinder would always quit later in the day.

Thanks
Scott

Sounds very much like a heat-related stator issue. Stators are very susceptible to heat & vibration, often causing intermittent, heat-related issues such as your's, especially if it tends to affect all cylinders vs. just one cylinder.

To verify which component is breaking down, you'll need to measure DVA on each component per our troubleshooting guide when the problem is occurring.

DVA Explained

DVA is a highly accurate measurement. But you must have a digital meter with a DVA Adapter attached.

This is the troubleshooting guide for your engine:

Mercury 2 Cylinder - 339-6222

If purchasing DVA equipment is impractical, we suggest printing off the troubleshooting pages & taking them & your engine to a qualified marine mechanic.