2005 J90PLSOA only firing on right 2 cylinders

[colt45guy]

Hey everyone,

New guy here--both to the forum, and to outboard motors.

I bought a neglected pontoon boat a few months ago as a project. It has a 2005 Johnson V4 90hp J90PLSOA motor. During the test run, it was obvious that it had some carburetor problems from sitting so long.

I rebuilt all 4 carbs with OEM parts and new gaskets, pulled the fuel tank and pressure washed all the crud out of it. Replaced all fuel lines, fuel pump, spark plugs and spark plug wires. The ignition switch was really corroded and the emergency cut-off clip wouldn't stay seated, so I replaced the ignition switch. All parts used have been Johnson factory parts--no cheap Amazon stuff.

We took it out on the lake, and it ran pretty well--had my 22' pontoon boat going 26 MPH. It was still hard to start and it didn't idle well so we ran it around the lake for about 20 minutes of WOT to flush any remaining dirt out of the carbs. Everything was going great until it lost power--happened instantly like flipping a switch. The motor kept running, but couldn't get back on plane. We limped it in, and I started tinkering....figured that the motor is 20 years old so I might as well replace anything that 'might' cause the problem.....and I'll have spares on hand if the parts I swap don't fix it.

I found a burned spot on one of the coil packs so I replaced both with brand new coil packs. Still ran rough/shaky, and I discovered that I'm only getting spark on cylinders #1 and #3 (right side)....the spark comes from 2 different coil packs, so either I got 2 bad parts, or there's another issue. Cylinders #2 and #4 (left side) are not getting any spark at all.

Replaced the power pack with a brand new OMC. No change--disconnecting spark plugs 2 and 4 makes no change in the way the motor runs--only cylinders 1 and 3 firing, rough/shaky and only stays running with the timing advanced.

I replaced the optical sensor too, and it made no change.

I disconnected the black/yellow wire from the power pack, then disconnected the yellow wires from the regulator. Neither made any change--no spark to 2 or 4.

I'm at the end of my rope here......I thought I was going to be smart by having an all new ignition system, and I've double and triple checked everything I've replaced.....but I'm quickly running out of time/money/patience.....

Any ideas?


Edited to add: I've tried disconnecting the temp sensors too. No change. I don't think this would be a cause, but this motor had the oil injector deleted and I'm running pre-mix 50:1

 

[saltchuckmatt]

Hey everyone,

New guy here--both to the forum, and to outboard motors.

I bought a neglected pontoon boat a few months ago as a project. It has a 2005 Johnson V4 90hp J90PLSOA motor. During the test run, it was obvious that it had some carburetor problems from sitting so long.

I rebuilt all 4 carbs with OEM parts and new gaskets, pulled the fuel tank and pressure washed all the crud out of it. Replaced all fuel lines, fuel pump, spark plugs and spark plug wires. The ignition switch was really corroded and the emergency cut-off clip wouldn't stay seated, so I replaced the ignition switch. All parts used have been Johnson factory parts--no cheap Amazon stuff.

We took it out on the lake, and it ran pretty well--had my 22' pontoon boat going 26 MPH. It was still hard to start and it didn't idle well so we ran it around the lake for about 20 minutes of WOT to flush any remaining dirt out of the carbs. Everything was going great until it lost power--happened instantly like flipping a switch. The motor kept running, but couldn't get back on plane. We limped it in, and I started tinkering....figured that the motor is 20 years old so I might as well replace anything that 'might' cause the problem.....and I'll have spares on hand if the parts I swap don't fix it.

I found a burned spot on one of the coil packs so I replaced both with brand new coil packs. Still ran rough/shaky, and I discovered that I'm only getting spark on cylinders #1 and #3 (right side)....the spark comes from 2 different coil packs, so either I got 2 bad parts, or there's another issue. Cylinders #2 and #4 (left side) are not getting any spark at all.

Replaced the power pack with a brand new OMC. No change--disconnecting spark plugs 2 and 4 makes no change in the way the motor runs--only cylinders 1 and 3 firing, rough/shaky and only stays running with the timing advanced.

I replaced the optical sensor too, and it made no change.

I disconnected the black/yellow wire from the power pack, then disconnected the yellow wires from the regulator. Neither made any change--no spark to 2 or 4.

I'm at the end of my rope here......I thought I was going to be smart by having an all new ignition system, and I've double and triple checked everything I've replaced.....but I'm quickly running out of time/money/patience.....

Any ideas?


Edited to add: I've tried disconnecting the temp sensors too. No change. I don't think this would be a cause, but this motor had the oil injector deleted and I'm running pre-mix 50:1

Not sure I'm the man here but the key thing you said was "you limped it in" it might be in limp mode. You said you unhooked the overheat sensor....was that the port side? Port side sensor is the one that puts it in limp mode and there is a way to test that.

 

[colt45guy]

Not sure I'm the man here but the key thing you said was "you limped it in" it might be in limp mode. You said you unhooked the overheat sensor....was that the port side? Port side sensor is the one that puts it in limp mode and there is a way to test that.

I've tried it connected and disconnected. The port cylinders are the ones that don't have any spark......I'm gonna go try with a heat gun and see if that changes anything.

 

[racerone]

Have you looked at the water pump impeller ?

 

[saltchuckmatt]

I've tried it connected and disconnected. The port cylinders are the ones that don't have any spark......I'm gonna go try with a heat gun and see if that changes anything.

Better experts on here on the whole limp mode stuff. Port side has what I believe the brown wire and the white wire. Forget which wire causes that. By the way, that's the sensor that is really hard to get and expensive. I did kind of get ahead of myself, is water pump TT flowing? Did you get any alarm sounds? Have you done a compression test since this happened?

 

[colt45guy]

I've tried it connected and disconnected. The port cylinders are the ones that don't have any spark......I'm gonna go try with a heat gun and see if that changes anything.

Resistance values changed from open to 1K ohms when I applied the heat gun. Both temp sensors are working as advertised. This isn't a heat problem because it only runs on the starboard cylinders from a cold start.

Bonus problem!! I just burned out my starter. :-( It started dragging, and then seized up. Tapping it with a hammer gets it to spin a bit more, but it's toast.

Compression in all 4 cylinders is between 121 and 127--impeller is new with less than 20 hours on it. No alarms at all, and the temp sensors are working as expected. When I said 'limped it in', I meant that I got it back to the dock on 2 cylinders and less than half the speed we went out at.