Coil pack testing question

| This coil only appears to put out one spark on one side, the top | cylinder. The bottom cylinder doesn't fire and the plug is wet with | gas. I put in new plugs and not a mark on it when the top one showed | clear heat marks. I swapped the plugs, same deal. The coil wires are | solid core and both of them and their 10K spark plug caps test OK with | my multimeter.

Dumb question...

Have you swapped the wires between the two plugs to make sure that's not causing the "no spark"?

I assume that this is a single pack, so you can't swap coils around to see if the spark moves to the other plug, eh?

Yes, the wires are stranded solid copper which very seldom fails. The

It is a single coil pack.

I also tried running it with the coil pack in the air in case it had 'tunneled' a ground. That made no difference.

Mike

Time for a compression test.

i had a boat like that some years ago 105 chrysler. It would start and idle nicely but it would not accelerate. I finally put it in an auction.

Unfortunately I wasn't expecting to work on engines so I didn't have my tool kit with me for spark and compression tests.

The engine doesn't have a lot of hours on it. It wasn't blowing any smoke at all and the oil was perfectly clear so I really hope is isn't a blown cylinder. That would be kinda odd on a 4 stroke wouldn't it?

Mike

If swapping the leads between plugs moves the no-spark to the other one, that should certainly eliminate any possible cylinder problem. I'm presuming this is the "waste spark" setup where both plugs are fired at the same time, with one wasted on the cylinder on it's exhaust stroke.

If it is a waste spark system and you swap the wires between cylinders and it still runs the same, that would indicate either a bad plug or a cylinder compression problem if you know it is getting fuel. Swapping the plugs would isolate the plug problem if that is the case.

Lugnut

I just found out my meter was going dead so the readings went all over the board which tosses out most of my previous assumptions..

I got a new battery in it now and the meter readings are as follows at room temperature.

'Good' cylinder spark plug "10K" cap tests at 8.7K ohms.

'Bad' cylinder spark plug "10K" cap reads 9.7K ohms.

Primary between the two input wires, 9.4 ohms.

Reading between coil posts, 8.2K ohms.

Reading between 'either' coil post and the ground wire is infinity at my meters 2M ohm setting.

Reading between either coil post and the positive wire is infinity also.

Unfortunately the boat is 3 hours away.

Mike

Ok, it sounds like the plugs operate in series, i.e. the spark voltage goes out one coil post, through one spark plug to the engine block and back through the other spark plug and back to the other coil post. If this is the case, since you don't see any apparent leak to ground in the coil, your problem seems to be outside the coil pack. Sounds like you may well have a problem with the engine itself.

It could be the coil pack . IMO, they really cannot be tested much with an ohmmeter. Its possible some of the internal insulation has been blasted off the wires and it shorts out at RF frequencies and high voltage. What I have done in the past with automotive waste spark coils is to heat them in the oven for an hour at 150-200 degrees F (not C !!!) and then try the ohmmeter again. Iif you can find out the low side operating voltage (possibly 7.5 v), hook it to a reasonable appropriate voltage on one side and run the other wire over a rasp or something to simulate make / break. Make spark gaps between both high sides and ground. Do this while the coil is hot at 150F or so.

Unfortunately I have to rely on a meter, the wires are not long enough to swap.

Mike

mr158912 wrote:

Thanks for the ideas folks, it was a strange one.

My adult son and I went up with some diagnostic tools this time like my timing light and digital logic probe for testing the output and input of that coil.

I plugged it back together and started it and well... The freaking 'bottom' cylinder is now working and the top isn't... My kid is now chuckling, figuring out fast it's back to the drawing board... So... after carefully looking at bolt marks and a wire clip under a bolt mark we determined that I didn't put it back together wrong so I took it all apart and used a contact cleaner on the copper strands in the coil wire and the screw end for the spark plug cap and put it all back together and it purred...

Figures, your basic of basics, a bad spark plug wire connection.... that according to the local marina just 'Never' happens. Ya right only a coil or brain box fails, right. LOL!

This engine only has about 40 running hours on it, but sits out all season.

Mike

Mike Roma> I know this coil pack isn't off a car, it is off a Johnson outboard, but