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Johnson 90 HP 1985 J90TLCOS Electrical Doozy

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Bassboatin1

Contributing Member
Hey all! Im a new member but have used a few threads to try and trouble shoot my problem but have had no luck so far. I recently got a new project (couple hundred bucks) its a procomp 1540v bassboat with a 90 hp johnson on the back. The owner said it had an electrical problem that blows the 20a fuse in the motor. I put a new battery on, replaced the starter ( would spin but not rise when jumped) and have used a multimeter to verify power to the terminal and the solenoid. There is a big red connector that puffs a bit of smoke everytime I put a new fuse in and connect the negative terminal. Ive cleaned all terminals but this problem still persists to the point it is burning the inside of the red connector in two prongs. I put in a 20a ato circuit breaker and the burbing connector is emitting more smoke than ever. I am not even turnint the key just connecting the battery. Where do I even start with this? I am trying to take this project kind of slow but am getting frustrated. Searched the web high and low and cant seem to find this problem replicated anywhere else. Thanks in advance
 
How about the ignition switch? Verify no power in off position...only to the one post that is hot.
 
Hey timguy thanks for your response. I am a bit confused, so i would connect one end of the multimeter to the ignition switch power lead and the other to the problematic connector prong right? But the end of the connector is the hole side that leads to the battery. The prong side leads to the engine, so if it unplugged I would need to stick a multimeter from ignitionnto the hole corresponding to the problem prong while the battery is connected right?
 
Disconnect the red plug when you reconnect the battery. If the fuse blows with the red plug disconnected the problem is in the engine harness, if it blows with the plug connected the problems are on control/harness side.
 
So it looks like its in the harness control side. Thanks for the tip. Im discovering all sorts of problems on this project! Now I cant get the flywheel to spin wunless the spark plugs are removed. With the plugs on and the starter jumped from a battery it wont spin.
 
Compression tests are ALWAYS helpful. Mr. Scott is a very good and experienced mechanic. Has there been any wiring modifications between the motor and the controls? That's what I usually find leads me to the problem. Look for a possible short....hot wires to ground. Make sure that no power ever enters your kill wire.....that's the black with yellow stripe. If power gets into that wire, it will kill your main spark component.....the power pack.
If it's badly flooded, it will not spin over, unless the spark plugs are removed.
 
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Agreed.------Do the compression test , first thing to be done when you buy one .----Or BEFORE you buy one of these motors.-------Take the starter apart for inspection.-----People just crank and crank these motors and burn out the starters.----Easy to do !----Never done one , then just ask !
 
Wow this forum is fantastic. Thanks guys for all the help! I really picked the boat up as a project and to learn more about outboards, but yes stupudly did not perform a compression test. Frabkly I didnt think you could compression test without the flywheel spinning. Ive got a compression tester and have taken the plugs out but am having a rrally hard time trying to get a reading. I cant spin the flywheel in neutral by hand and i can spin it in forward by hand but only a little. The lower unit is making a noise in neutral but not spinning and makes a fair amount of noise in forward but the prop spins. How should I be compression testing this? Junping the starter and taking readings from each hole with the plugs removed? Thanks for your patience with me .
 
Drain / inspect the gear oil.----Remove lower unit.----Pull motor over with a rope for the compression test.----To me your project is starting to sound like a BOAT.-----BRING ON ANOTHER THOUSAND ----before you get it running properly.
 
There are other methods to check cylinder/piston condition using "leak down".....or pressure loss over time. This takes more equipment to do. With your compression tester, screw it or push/hold it (old fashioned gauge) in each cylinder. Make sure all spark plugs are out. Crank motor at least 5 revolutions with electric starter. Don't get hands in the way, of course. Might need a helper to crank over the motor for you. 4 stroke motors....not your case, however, need to have the throttle open, for an accurate test.
 
Ha! That is not the first time ive heard that! So when i went to drain gear oil there is absolutely no oil draining out, my tubes on the mityvac are too stiff to run down into the unit. I will take the lower unit off and report back.
 
You might first want to determine what if any issues there with the lower unit.-----Remove bypass covers to look at the pistons and rings too.-----Don't spend any coins until you determine if your motor is in reasonable shape !!!----Testing and inspection needs to be done !
 
Maybe there is nothing wrong with the lower unit. Can you describe again the symptoms...?? Does the motor turn freely? In and out of gear?
 
Yeah so the flywheel turns in all gears but is sort of reluctant to turn past the halfway mark, but will turn. This is with spark plugs out. The prop spins in F and in R but doesnt spin in N. I assume thats correct. Last night when i jumped the starter with no plugs the flywheel spun freely. Havent tried that again yet.
 
Then the next thing to check is the boat.----Free or nearly free boats often cost thousands of $$$ to get them in safe condition to use.----Just look everything over carefully before spending any money on this outfit !!
 
The transom is good, it needs new carpet, it has a soft spot on on side of the floor but not a huge deal. It obviously has an electrical problem but thats all ive been able to find out so far
 
90 PSI is not good here.------Perhaps a lousy gauge.----The FOUR bypass covers are on the sides of the block.----Six screws each as clearly stated.
 
Okay okay apologies still learning here. So if all cylinders were 90 psi thats still not a good reading? I stopped turning the flywheel at 90 as I figured this was solid compression.
 
Uh okay. Thanks for the help i guess. Im new to this and appreciate your input. Not a huge deal if the thing is toast just trying to learn more about it. Thanks anyway.
 
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