What does this mean - unplug Cyl#3 with no effect

In chasing down a problem not getting to WOT RPMs on a '99 Evinrude 50 4-stroke, it first sounded like he neutral switch was stuck. Checked everything out with a ohm meter and it was fine.

Following the manual, I checked all of the coil resistance measurements all the way back to the ECM and all were fine, thinking it was a bad coil. Just trying different things, and I unplugged the coil on Cyl#3 and the motor will start and idle with no change in the idle, but if #1 or #2 are unplugged, the motor will die if running, or will not start so I figured that the #3 coil is bad BUT, when I swapped the #1 and #3 coil, it did the same thing so it can't be the #3 coil. It looks like it can run/start on #1 and #2 but not #2-#3 or #1-#3.

Checked the wiring back to the ECM and there is continuity so it is not a wiring issue.

Any ideas?

Re: What does this mean - unplug Cyl#3 with no effect

Need to check for presence and quality of spark from the #3 coil. AutoZone and other auto supply stores have cheap testers were the gap can be adjusted. Should get a bright blue spark across a 7/16 to 1/2" gap if working.

-- Jeff

Re: What does this mean - unplug Cyl#3 with no effect

Normal spark jump test does not work on a 4 stroke. There is no rule of thumb on how far the spark is supposed to jump, and I have tried it personally.
I would suspect the injector for that cylinder. They are easy to swap; switch it with one of the other cylinders and see if the problem follows the injector.

Re: What does this mean - unplug Cyl#3 with no effect

daselbee said:

Normal spark jump test does not work on a 4 stroke. There is no rule of thumb on how far the spark is supposed to jump, and I have tried it personally.
I would suspect the injector for that cylinder. They are easy to swap; switch it with one of the other cylinders and see if the problem follows the injector.

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Not that I am disagreeing with your statement, but I am wondering why the spark test won't work on a 4 stroke outboard? It works on every other spark-ignition engine I have ever worked on.

Re: What does this mean - unplug Cyl#3 with no effect

The spark produced by the EMM will not jump the 7/16" gap, but will jump the .030 plug gap. The EMM provides 12v to the coil constantly, and the other lead from the coil is switched to ground abruptly by the EMM at the proper time. The voltage collapses so fast in the coil, that it generates the HV secondary which then jumps the plug gap. All I can offer is that this HV secondary is not the same high KV voltage that a CDI style ignition develops. I have one 70 HP Evinrude 4 stroke, and one 70 HP Suzuki 4 stroke (same engine), and neither of the will allow a 7/16" spark gap jump. If you close it down to maybe 1/8", then it will jump.

As a related issue, I am having a real problem getting my timing light to trigger right on these ignition systems also.

The engines run good and strong.

I asked haffiman over on marineengine, and he replied there was no established "spark gap jump" test. Haffiman, Morton Ringvold, is one of my go to guys...he knows his stuff.

So...I leave it at that. I would ask that if the OP gets a spark gap tester and uses it, that he post back his results.

Re: What does this mean - unplug Cyl#3 with no effect

Thanks for the info daselbee, I was just wondering. So with your experience here, with a spark tester, it should jump a smaller gap (1/8"). Was the spark on your setup, at that gap, a fat bright blue spark? The main thing the OP needs to figure out here is which of the 3 things (spark, fuel, compression) his engine is lacking on number 3.

Re: What does this mean - unplug Cyl#3 with no effect

guy74 said:

Thanks for the info daselbee, I was just wondering. So with your experience here, with a spark tester, it should jump a smaller gap (1/8"). Was the spark on your setup, at that gap, a fat bright blue spark? The main thing the OP needs to figure out here is which of the 3 things (spark, fuel, compression) his engine is lacking on number 3.

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I agree, and I wanted to determine if there was a spark before moving on. I feel fairly confident that there should be since the problem did not follow the coil, but a true spark test would confirm that absolutely. Either that or there is no signal from the ECM which is a whole other world of hurt $$$$$

I think that there is some merit in the bad injector because the spark plug when pulled is clean, no residue or fuel, and there is no excess unburnt fuel in the exhaust. To me that could indicate that Cyl #3 isn't getting any fuel. I will also look at swapping the injectors around as well.

Re: What does this mean - unplug Cyl#3 with no effect

Could somebody point me to what I need to check the spark, assuming the automotive test may not be correct.

Thanks.

Re: What does this mean - unplug Cyl#3 with no effect

Just put the plug back into the wire, ground the body of the plug against the motor, and crank it. Should be able to see spark at the tip of the plug. That at least would show if you have a no spark condition or not.

Re: What does this mean - unplug Cyl#3 with no effect

spaynter said:

I think that there is some merit in the bad injector because the spark plug when pulled is clean, no residue or fuel, and there is no excess unburnt fuel in the exhaust. To me that could indicate that Cyl #3 isn't getting any fuel. I will also look at swapping the injectors around as well.

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I can't absolutely say the exact proper way to check for spark on these 4 strokes. For your purposes, plug in boot and grounded to the block will do, just as posted above. That will give you a go/no go. If you have to get down to the fine tuning and quality of the spark later, then you can figure out the proper spark test method.

You know the injector circuit? It is almost the same as the ignition circuit. The EMM provides 12v constant to one of the two wires at the injector. Then the circuitry in the EMM turns ON the other wire (in other words, switches to ground), completing the path to ground for the injector. You CANNOT disconnect the two wire injector connector and measure voltages when the engine is running. You must measure any voltages using some sort of breakout wiring device, or probe through the insulation. One wire will read constant 12v and the other will read between about 6 to 10v using a DVA meter, depending on the duty cycle of the injector when running. Hard as hell to test these without the proper breakout cable.

Re: What does this mean - unplug Cyl#3 with no effect

daselbee said:

I can't absolutely say the exact proper way to check for spark on these 4 strokes. For your purposes, plug in boot and grounded to the block will do, just as posted above. That will give you a go/no go. If you have to get down to the fine tuning and quality of the spark later, then you can figure out the proper spark test method.

You know the injector circuit? It is almost the same as the ignition circuit. The EMM provides 12v constant to one of the two wires at the injector. Then the circuitry in the EMM turns ON the other wire (in other words, switches to ground), completing the path to ground for the injector. You CANNOT disconnect the two wire injector connector and measure voltages when the engine is running. You must measure any voltages using some sort of breakout wiring device, or probe through the insulation. One wire will read constant 12v and the other will read between about 6 to 10v using a DVA meter, depending on the duty cycle of the injector when running. Hard as hell to test these without the proper breakout cable.

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Thanks. I was hesitant to simply pull it and ground to the block given the EMM and all. Strange things can happen to electronics when you put grounds and signals where they aren't expected and I wouldn't want to damage it.

I will be relying on the service manual to find things, but it is pretty good and I can follow easily enough. I may be able to put a thin wire into the connector since it only a 12v signal.