"Slow Mo" Problems with 1994 OMC 150 hp

[M.O.M.III]

The 1994 OMC engine is on a Fish 18, 1991 Wellcraft hull and has been in and out of the shop for the past several years with the same problem. On random occasions, the engine goes into "slow mo" like it is overheating. To get the engine to reset, the engine has to be turned completely off and restarted. It is not overheating and might only happen once every fishing trip or on other occasions, might happen 8 or 10 times. Sometimes the horn goes off, but most times it does not. I know it sounds like it is overheating, but in one instance I have reset the engine and immediately traveled over 20 miles without it happening again. We have changed the sparkplugs, the power pack and have disconnected the heat sensors to no avail. This happens in the summer and the winter, so I do not think it has anything to do with the water temperature. As I mentioned, once the engine is reset it might be fine for the rest of the day and sometime it runs all day with no problems. If the engine is not reset, it stutters and will not get above 2000 rpms. Any suggestions besides sinking the engine will be greatly appreciate. Thanks, Martin

 

[almost retired again]

Re: "Slow Mo" Problems with 1994 OMC 150 hp

Hello M.O.M.<br />All it takes for slow to be activated is for one of those tan wires to go to ground. With all that has been done to that engine I think that I would start inspecting all of the wireing harness, maybe one of the wires has been chaffed enoung that it will sometimes touch ground either by viberations , or hitting a wave wrong. Don't overlook the area around the hot horn.<br />Hope that you find the problem, I've always thought that engine to be a great engine.

 

[clanton]

Re: "Slow Mo" Problems with 1994 OMC 150 hp

This engine is 60 degree V6 right? Should have 5 sensors for alarm system. 2 overheat sensors one for each head, low oil in tank sensor, no oil sensor on vro pump, and fuel restriction sensor. All of the sensor signal wire (tan) go to the same termial and connect to the alarm horm. The only one that will set S.L.O.W. is the overheat sensor.In the engine harness there is a blocking diode that blocks stray voltages, and the other sensors from setting S.L.O.W. ,locate and check this diode, check all tan wires for short to ground or hot. Insure that alarm horn and oil tank is correct for this engine. You may need factory manual and wiring diagram to locate diode. I only have genric manual for this engine, it show the diode, but not the location. If all of this doesn do it, bad pack???

 

[clanton]

Re: "Slow Mo" Problems with 1994 OMC 150 hp

I read your post again, I see that it is 91 boat with 94 engine, If the old controls and horn were used with new oil tank, or new horn used with old oil tank, that may be problem, there was a Sb,or info letter on mixing oiltanks, alarm horm, but cannot find it, will keep looking. SB 2313 dated April 97<br />address a problem with the thermostats the kit number is 435597.

 

[clanton]

Re: "Slow Mo" Problems with 1994 OMC 150 hp

Blocking diode should be app 5 1/2 inches from large red harness connector in the engine harness.