1984 Evinrude 115 HP running rough at idle

I have a 1984 115 V4 Evinrude outboard (E115TLCTE) which runs great under load, tons of power, but misfires and stalls at idle making docking very difficult. Plugs are clean, no fouling, even though problem has been like this all of last summer....checked all jets, new looking and consistent size (checked with closest number/letter drill as gauge)

I put a high speed digital oscilloscope on (DC clamp on measuring current on spark plug wire), and found Cylinders 1 and 3 fire together, and also 2 and 4.

My understanding was that there was a clear firing order of something like 1-3-2-4, but that doesn't seem to jive with what I am seeing. I also noticed that firing current was weak at time....barely firing at all on cylinder 1...

Swapped the two ignition modules....problem did not follow the module. Tested 12V to coil current versus plug current....they are consistently the same, but 12V pulse is sometimes dropped or weak.....

I also did diode test (good), and checked sensing coils with Digital meter....says voltage should be > 0.3V in manual, all I can see is 0.07V on all 4....wonder if using a DMM to record high peak volt (built in function) is different than the old fashioned analog meter in this respect, but this could explain why misfiring a low rpm.

Is it possible the magnets in the flywheel are weak or something else is going on that would make the firing weak at low RPM, but great at high?

Note that when engine backfires, it tends to blow water out of exhaust, and stop engine spinning dead cold. Another weird thing is that if I put into gear at idle, the random backfiring seems to calm or disappear.......this is also very puzzling)

Anyone have experience with this or could give me a few pointers?.....don't know what to think at this point....very frustrating. Dan

Re: 1984 Evinrude 115 HP running rough at idle

Possible you are describing a "lean sneeze" as a symptom. An occasional cough of the engine at idle. This is a carb problem, not an ignition problem. Possible the idle circuits (passages) in the carb bodys are restricted with perhaps dried fuel. When at idle the carb butterflys are closed and the fuel goes thru special idle passages. If this is your problem, some Gumout type carb cleaner will take care of the restriction.

Re: 1984 Evinrude 115 HP running rough at idle

I like your description of "lean sneeze", because that's exactly how it sounds....run run cough run cough run run run run cough run run run run run cough stall....like she's coughing through her nose and blowing water out the two rear ports.

I like your advice, will try some carb cleaner to see if it affect / cures the problem...much more attractive than tearing into the engine's ignition system. I'll let you know how I make out. Thanks. D

Re: 1984 Evinrude 115 HP running rough at idle

Check spark plug wire routing and timing, too if you have a minute. Incorrect timing or arcing and crossfiring on the plug wires will cause that problem at idle as well. Firing order is 1-2-3-4 if I remember correctly.

Re: 1984 Evinrude 115 HP running rough at idle

BKS72 said:

Check spark plug wire routing and timing, too if you have a minute. Incorrect timing or arcing and crossfiring on the plug wires will cause that problem at idle as well. Firing order is 1-2-3-4 if I remember correctly.

Click to expand...

I have done that already, its pretty much impossible to have this happen because the 4 coils are mounted on the side if their respective cylinders, and the electronic modules have factory keyed connectors.....you'd pretty much have to modify the wiring to screw it up..... but, as the saying goes about "forest for the trees", I will look again. Thanks

Re: 1984 Evinrude 115 HP running rough at idle

I meant if you have plug wires crossing over one another as they go from the coil to the plug. If they are old sometimes they can arc across and you'll have 2 cylinders firing at once

I had a buddy swap powerpacks and when he put one of the the packs back on he swapped the leads from the pack to the coils. Timing was 180 out. You're right, the connectors to the packs are 1 way but the wiring out of the pack to the coils can be swapped.

It is probably fuel as the first response said but if you have the timing light it only takes a couple minutes to check pick up and WOT timing.

Re: 1984 Evinrude 115 HP running rough at idle

Sorry, I understand your point now. As far as arcing, I did pull the high voltage leads out of the metal clips, separated and had them away from all metal and each other....ran the engine, made no difference, so I'm pretty confident the wires aren't arcing. But you make a good point about the wiring, will definitely take a look. Thanks for the advice.

Re: 1984 Evinrude 115 HP running rough at idle

Watch it at night, any arching will be easy to see.

Re: 1984 Evinrude 115 HP running rough at idle

analog meters have a internal resistance to them and will affect voltage readings in a low voltage ignition system such as what ur looking at where a DMM will not affect the circuit near as much. since u are familiar w the oscilloscope i would like to suggest use of a low amp probe if u have one on the power input to the coil (each one one at a time) watch the pattern for consistancy between coils as well as following a general description of a sharp rise followed by a almost strait down drop off and a small negative dip from field collapse if u see a lower rise on one coil or a plateau instead of a point at the top u have a weak coil u can also use a open air spark tester set it to 7/16 gap to stress test and monitor same way to be sure they can go max load without voltage loss

EDIT: one other note coils can be checked for shorts in windings by ohm readings but if u have the means watching them w a low amp probe on a scope is far more accurate ive seen coils ohm correctly and fail on a scope

Re: 1984 Evinrude 115 HP running rough at idle

I had a very similar problem to yours, I bought the boat with a miss and it ran ok up top... after I changed my coils I cleaned the carbs. ran worse... adjusted the idle to back to the correct mark, adjusted the throttle cable to the new mark and she runs great all the way from idle to wot... before I changed everything the boat was topping out at 27mph and just felt sluggish with acceleration... tonight had it up to 36mph and it responded great... such a difference.