1986 Evinrude 90 V4 Running Rough

[TheFishAreLaughing]

Hey guys, I purchased a 1986 Sea Nymph '19 Fish N Ski with an Evinrude 90 V4 in July of this year and up until now it has been purring like a kitten. Last weekend when I took it out on the river I noticed it was running rough with some power loss so I turned around and came back in. I was running it at the house on muffs for diagnostics and quickly determined by pulling spark plug wires that the port side bottom cylinder is not firing. I have tried, in order, swapping spark plug wires, coils, and spark plugs with a functioning cylinder to see if the problem moved. It did not. In the process I determined that it is definitely getting a good strong spark to the spark plug. Any suggestions on what to try next?

 

[racerone]

Compression test !

 

[TheFishAreLaughing]

I was afraid that was going to be the answer.....I guess I will be buying a compression test gauge tomorrow. Assuming the compression is close on all 4 cylinders, what would be the next thing to check?

 

[emdsapmgr]

After you do that all important compression test: check to see if that cyl is getting any fuel. If it's got spark and fuel you should get some firing. If the jets that feed that cylinder are plugged in the carb, that cyl won't fire. Worse, if it's not getting fuel, it's not lubricating that cyl. A much worse consequence. That's why the compression test is so important.

 

[TheFishAreLaughing]

When I pulled the plug earlier it looked wet, but I could not smell any gas on it so that could have been an illusion.

 

[racerone]

????---The plug is wet because the cylinder is not performing properly.------Due to poor crankcase compression / poor scavenging / possible low compression.---The sparkplug simply does not get hot to keep itself clean !

 

[TheFishAreLaughing]

The point I was making was that if the cylinder was getting fuel without firing, the spark plug would be wet. While it looked wet, I could not smell any gas on it, so I suspect it may not be getting fuel.

 

[durban]

Change the firing order at power pack example if its 1 2 3 4 make it 4 3 2 1 your no 4 becoming your no 1 if you do not have the instruments to check pulses or a DVA meter .by doing this you will find the for example if no1 does not spark & by changing the firing order it moves to no 4 becoming the no1& still doesn't spark on no4 this tells you the problem is in the power pack. If it fires on no 4 it tells you the problem is with the no 1 hall sensor .

 

[Faztbullet]

??????? What Hall sensors???

 

[durban]

In his case he may have the trigger assembly cast in the epoxy they got smart by doing it in comparison to the earlier models being a1986 model all triggers as the little knowledge ive got work on the Hall Effect .

 

[emdsapmgr]

Another possibility. If you have a bad head gasket, it could be leaking water into that cyl. Enough water and it will put the fire out. You may want to pull that head and check the head gasket seal ring around that non-firing cyl.

 

[TheFishAreLaughing]

Ok, just completed the compression test: The cylinder that is not firing is 79 PSI. The cylinders that are firing are as follows: 78 PSI, 80 PSI and 76 PSI. Compression test was done with the engine cold and all 4 spark plugs removed.

 

[TheFishAreLaughing]

Just found something, don't know if it could be the cause of my problem or not. I found what looks like a vacuum hose disconnected below the carburetors. Pics below of both before and after I re-connected it. I have not tried to run it yet to see if it made a difference.

 

[racerone]

Normal compression on that motor would be around 120 PSI.----Could try another tester or -------And that wee hose is to get rid of any spillage / leakage into the intake silencer box.-----Doubt it will change how the motor runs.

 

[TheFishAreLaughing]

Hmmmmm......don't know how accurate the gauge is, it is a cheap brand but it is brand new.....and the results were consistent. Running on 4 cylinders that motor would push my boat at 39 mph trimmed out. With only 3 cylinders it would still do 32 mph.

 

[Faztbullet]

In his case he may have the trigger assembly cast in the epoxy they got smart by doing it in comparison to the earlier models being a1986 model all triggers as the little knowledge ive got work on the Hall Effect .

Nope ...no hall sensor in epoxy triggers they are coils.....

 

[emdsapmgr]

The hose that was not connected appears to be the airbox drain hose. Sucks unburned carb fuel/oil back into the bottom cylinder for combustion. It should be connected but has little to do with the engine running. That 86 engine has the low compression heads on it. I'd look for normal compression in the 95# range. You might get your compression up a little if you ran some Bombardier Engine Tuner through it. Maybe a couple of times.

 

[sutor623]

What triggered this rough running incident? Did it happen after running, or did it just act funny from the second you put it back on the water?

 

[durban]

Nope ...no hall sensor in epoxy triggers they are coils.....

Does,nt matter it still works on the Hall effect.

 

[Faztbullet]

Does,nt matter it still works on the Hall effect.

You need to study up your electrical as a Hall sensor has power to the transducer and magnet triggers it to discharge. A outboard trigger has NO voltage to it as the encapsulated coil generates the positive voltage as the magnet passes by as the SCR in pack only triggers on a positive charge, Here is a digram of how a trigger and pack work....As you see it a coil and a coil does not work by Hall effect...