Logo
FULL SITE MENU

2004 50 HP J50PL4SR won't rev above 3000 rpm

M

mojojohnson

New member
Launched pontoon after winterizing at dealer.
Motor started ok, but will not go above 3000 rpm; and shakes badly. Seems to run ok below that engine speed.

Bought the 2004 Johnson Service manual for 50 HP 4 stroke 4 valve EFI motor. Symptoms above seem consistent with the Engine CAUTION system being triggered somehow; but there are no lights or warning horns from the switch on startup.

Low oil level? checked oil level- full and clean.

Water temperature? Strong cold water stream from fitting.

Cylinder head temperature sensor? disconnected cylinder head temp. sensor; started motor; alarm horn sounded and CHECK ENGINE light came on; but still would not rev above 3000 rpm. Reconnected sensor and restarted- no alarm and no CHECK ENGINE light; but still would no rev above 3000 rpm.

Exhaust manifold temperature sensor? same as above.

Any thoughts or suggestions? I don't have electronic diagnostic skills, but can probably find and figure out an ohm meter. I'm reluctant to haul it to the dealer if I can diagnose and repair.

Thanks in advance for your comments and expertise.
 
Thanks, racerone and daselbee. Being a newbie- what exactly should I be looking for on the neutral shift switch? I'll checkit out this weekend.
 
It is either on or off. Just a switch.
But the issue is this....which way is it when in neutral, and which way is it in gear? I don't know if it should be closed in neutral or open.

But I do know for a fact, that if the switch fails, and the motor THINKS it is in neutral, it will do as described.

So, meter across the switch in neutral, shift to gear, and if meter doesn't change, you know the switch is effed.

On a Df70 the switch is on the stbd side, way down low below the lower cowling level, near the oil filter, and definitely on the throttle linkage system, so it can be actuated when placed into gear. I hope this helps you physically find it. If you watch the linkage move, you will see the switch.

It is adjustable, too, by the way.
 
Thanks Daselbee!. The neutral switch was fine, but one of the plugs was very fouled. Replaced them all and it runs like a top!.

Thanks again for the advice.
 
the question still remains mojo what caused the plugs to foul in the first place,lack of maintenance?4 strokes rarely foul,curious to know.
 
Good question- While I change the oil and lower unit regularly, I know the plugs have been in there for 8 seasons. I hope that is the reason and not something more troubling. It was the bottom cylinder.
 
Dealer did winterize the motor; supposedly running the motor prior to pickup. It did not start quickly at launch, and ran somewhat rough, so I suspect checking sparkplugs is not part of the package. Guess I will be taking a more active role in my outboard maintenance schedule now that I have the manual.
 
thanks for the reply mojojohnson.time to find a new dealer that plays a more active role with their work. Or do it yourself!!
 
Last edited:
So the shaking, as suggested in the first post, was NOT the SLOW mode kicking in.

When SLOW kicks in on these motors, I guess it is best described as a quick oscillation , up and down, in RPM...rev up, then down, then up, etc. in fast succession.

I must come to the conclusion that the original post was NOT describing that revving, but just describing a miss.

Is that right?
 
Back
Top