48SPL Running On One Cylinder

[Practical Outdoorist]

I have a 1990 Johnson 48SPL. 90 PSI on each cylinder. Spark through both plugs. Yet only the top cylinder is running. If I pull bottom plug wire ... NO difference in idle. Put it back and pull the top ... motor shuts off. Unspent fuel in bottom cylinder. I swapped the carbs to see if the problem would follow. It did not. Getting milky oil from exhaust. BTW I have a Jet Pump on this Motor. Could this problem be exhaust related?? I appreciate any help I can get. Thanks.

 

[hardwater fisherman]

How did you test spark?

 

[Practical Outdoorist]

I used an in line spark plug checker from Advance Auto.

 

[Practical Outdoorist]

I did OHM test on the ignition coil. Both Primary coils tested at 0 OHMs. Bottom secondary tested at 266 OHMS, Top at 344 OHMS.

 

[flyingscott]

you need an open air spark tester.Make sure the spark jumps 7/16" of a gap. Also get a different compression tester because 90 psi is not good.

 

[Practical Outdoorist]

Ok I will get these and test again.

flyingscott;n10676159]you need an open air spark tester.Make sure the spark jumps 7/16" of a gap. Also get a different compression tester because 90 psi is not good.[/QUOTE]

 

[54bobby]

Could be exhaust cover plate gasket or even hole or 2 in the plate from corrosion. I do believe that would also effect your compression

 

[racerone]

54bobby------Is there an exhaust cover plate that can leak water into this motor ??----And how can a leaking " exhaust plate " change compression on motors that have that part ?

 

[54bobby]

54bobby------Is there an exhaust cover plate that can leak water into this motor ??----And how can a leaking " exhaust plate " change compression on motors that have that part ?

not sure on that motor and i wasn't saying that was it but that was the case in my 69 25hp. pin holes in the inner cover leaking water into the cylinder. as for compression, if water can get into the cylinders isn't it safe to say that a bit of compression can get out through exhaust?

 

[racerone]

When compression starts the exhaust ports are blocked off.---There is no separate inner plate on this motor.----The block and exhaust passageway are all one piece.-----The only gasket in the picture is the head gasket.-----The owner was asked to repeat the compression test in post # 5.----There has been no response from the owner on that.----Which is not a surprise.

 

[Practical Outdoorist]

When compression starts the exhaust ports are blocked off.---There is no separate inner plate on this motor.----The block and exhaust passageway are all one piece.-----The only gasket in the picture is the head gasket.-----The owner was asked to repeat the compression test in post # 5.----There has been no response from the owner on that.----Which is not a surprise.

I will get the tools and re-test but the boat is in my driveway and two solid days of rain. I will report my findings back by this weekend.

 

[Practical Outdoorist]

Ok Guys, I got another Compression tester, Both cylinders the same at 125PSI. I also got the air gap spark tester, Top spark tested good. Bottom did NOT meet the required 7/16 test. I just want to restate that bottom coil test 266 OHMS, Top coil test 344 OHMS . So is it the coil?? or could I also need the power pack??

 

[racerone]

?---Switch the coils as a test.

 

[Practical Outdoorist]

It is a dual coil pack

 

[racerone]

?---Just switch orange wires.------Test stark with your tester.---Report what you see.

 

[flyingscott]

If your coils are good my guess would be your ignition module. I believe your model has the UFI ignition which is problematic.

 

[Practical Outdoorist]

?---Just switch orange wires.------Test stark with your tester.---Report what you see.

I switched the orange wires and got the same result. Top coil wire has spark, Bottom coil wire has no spark.

 

[racerone]

Sounds like a " kaput " coil.

 

[Practical Outdoorist]

Thank you all !! I will get a new coil and report back.

 

[Practical Outdoorist]

Sounds like a " kaput " coil.

I got the new coil today. Installed and had great spark to the bottom coil and better spark than I had at top coil wire. Driveway test with hose and confirmed that both cylinders are firing now. Unfortunately the weather is turning here and it will be a cold water test drive. I really appreciate the walk through and helping me solve this problem. It was and will be a learning experience.