OMC System Check / Slow problem

[Double J 300]

Gave my son a 1999 Johnson 115 low hours as I got it new. I used to be an OMC tech. The motor appears to go into SLOW (2500 rpm max) for no apparent reason intermittently. Temp gauge stays at cool, no horn or system check light. I had a new power pack and had him install it...same effect. Could it be a bad overheat sensor for SLOW (white wire)? Anyone see this before? Can the SLOW sensor be disconnected to end this? The tan wire will still sound the horn and system check light, correct? Motor is immaculate, all grounds as new. Did it for me only once when I had the motor two years ago. Thanks, Alan

dblej@tampabay.rr.com

 

[Walker]

Re: OMC System Check / Slow problem

The tan lead operates the SLOW system. The white lead operates the quick start. Yes you can disconnect the tan lead to see if its the temp sensor causing it to go into SLOW

 

[seahorse5]

Re: OMC System Check / Slow problem

Gave my son a 1999 Johnson 115 low hours as I got it new. The motor appears to go into SLOW (2500 rpm max) for no apparent reason intermittently. Temp gauge stays at cool, no horn or system check light.

You may have a bad guage or wiring problem and the motor is overheating, but not registering an alarm as an overheat is the only problem that will put that motor into SLOW.

With the key ON and motor OFF, ground either tan wire at the cylinderheads and see if the HOT lite comes on. The horn will not blow as that only works while the motor is running. It should beep when the 4 lites come on when you first turn the key to ON.

There is a possibility that the blocking diode that keeps the overheat warning from the rest of the system is shorted and any other problem or shorted wire could send the motor into SLOW. Use the factory manual for location and testing procedure.

 

[Double J 300]

Re: OMC System Check / Slow problem

Thanks for the replies. I will have him check out the tan wires on both sides for a short. I'll have him pull both heat sensors just to look for something. For clarification: when this happens, the temp light on Tach never illuminates, the horn doesn't sound with key on, and the external engine temp guage shows no overheat. The thermostats and housings are clean and operating so I can't see one bank getting an overheat alarm causing slow. I hate these type of problems, but at least a customer doesn't have to yell at me about lots of billed hours trying to get the symptom to show up. I still have access to OMC parts, so maybe a couple new sensors won't hurt.....could be a bad system check tach...had that once on a 150 hp....saga continues....