Intermittent miss 1996 225 OMC

[Ed Kelly]

" I have been having a problem

" I have been having a problem with my 1996 225 hp Johnson for a couple of months now. After running fine for an hour or more it will "bog down" and not run above 2800 rpm. I have not been able to reproduce the problem with a mechanic present. Yesterday it happened again and I was able to determine that I had no spark on the starboard bank. I am assuming that the problem is either the power pack or the shift switch. If I disconnect the shift switch connector (black/yellow wire), while I am having the problem should I expect to have spark again if the problem is in the shift switch? Is there anything else that would be likely to cause this? All components have tested good with the engine off , but I have not been able to do any output tests with the engine running while the problem is occurring. "

 

[joereeves]

"Ed.... Your engine incoporate

"Ed.... Your engine incoporates a ignition cutoff circuit that will engage whenever the engine starts to overheat, which will drop the rpms down to what you mention. Look at the top area of the starboard head... there should be a white wire with a black stripe leading out of the heat sensor. To disengage the ignition cutoff circuit, simply disconnect that wire at its plug in connector. If that cures your problem, you obviously have a intermitent overheating problem. This could be due to a number of things... trim too high, picked up a plastic bag, lower unit drawing air in a turn, etc....OR.... that particular heat sensor is faulty.

I'm assuming that your warning horn does beep when you turn the ignition key to the on position, and that with the key on, you can make the horn blow steady by grounding out the tan wires that lead out of the heat sensors on either cylinder head.

Another thing that might cause your problem is a ignition switch that has a high resistance short across the ignition kill circuit. The easiest way to check that is to eliminate that circuit by simply removing the black wire that has a yellow stripe for the back of the ignition switch. From what you've said however, I'd be more inclined to lean towards the ignition cutoff circuit (white wire/black stripe.

Joe

"

 

[Ed Kelly]

" It's definitely not the

" It's definitely not the S.L.O.W. that's causing the problem - I am familiar with that kind of failure. When that cuts in there is a "kicking" effect as I believe the motor runs on all six until it reaches 2500 rpm, then the limiter cuts in to drop rpm. The warning horn works on startup and I have tested it by shorting the tan wire. It's not an overheat condition - I have water pressure and temp guages and they read fine. When it shuts down the motor runs smoothly (compared to the S.L.O.W. mode) , just with no power - I am pretty sure it is only firing on three cylinders. I have ~800 hours on the motor so rigging is not a factor. I am pretty sure I am losing spark on one bank of cylinders, just not sure where to put the blame.

Ed "

 

[Ed Kelly]

" I ended up replacing the pow

" I ended up replacing the power pack as disconnecting the black/yellow wire when the problem reoccurred had no effect. Two weekends of running the motor with the new power pack and the problem hasn't come back, so it looks like that is where the problem was.

Ed "