1992 Merc Black Max 150

[bassinT]

I'm having 2 problems with my motor:

1) I can crank the motor when I first put it in the water and it will run as far as I want to go without the warning horn sounding. However, after I shut the motor down, and then turn the key back on, the warning horn will sound (even after it has been off for several hours) and it will not quit buzzing even before I have cranked the motor. When I crank the motor the warning horn continues to sound even though plenty of water is coming out the telltale. After the boat sits for 24 hours or longer I can crank it with no warning horn sounding until I run it and then start to crank it again.

2) I was running my boat at the lake last night about 3000 rpm and the motor started to bog down (it had been running fine all day). When I pulled back to neutral it cut off. After this I could crank the motor and it would run in neutral if I would give it gas and keep it above 1000 rpm. In neutral I can rev the motor and it revs up and runs as long as I keep it above 1000 rpm, but when I put it into gear it will bog out. I finally manged to get it running in gear and it would only reach 1750 at WOT. I'm going to hook an auxillary tank and see if maybe it's just water in my gas (I hope it's something that simple). If it's not bad gas then I was wondering what else I should check and I wondered if this problem could be related to the warning horn sounding??

 

[jchagnard]

Re: 1992 Merc Black Max 150

It sounds like the same problem I'm having. My motor ('95 Merc 135 XL) had the same symptoms. The oil warning (intermittent beeps) would sound and boat would come off plane to idle. Can shut it down for a while and problem goes away. Start up run for a bit & it comes back. Was told by a ret. mercury shop foreman that the oil warning control module will cut fire to #4 & #6 cylinders to keep from ruining the powerhead. I'm at the end of diag. my problem. Am down to oil pump sensor or the oil warning contorl unit as all other mechanical systems have checked out (visually inspected pump shaft gear, nylon worm gear, and measured pump oil output). Hope this helps.

 

[Texasmark]

Re: 1992 Merc Black Max 150

Bassin T, when your engine does what you said, pull the temp switch(s) wire(s) and measure the resistance. You could have a bad sensor or two (in the '95 model they use one on each head. I understand on early models they only used one on the starboard bank.) Also measure it when the horn is quiet.

Son had a sensor develop some resistance which caused the horn to sound when it wasn't supposed to. Replacing it cured the problem.

I don't know what the closed resistance of that switch is (when you have a bonafide over temp) but I'd suspect it's like a short circuit (less than 1 ohm between the engine block and the tan sensor wire) when the engine is over temp (over 195F) and an open circuit at all other times. I also don't know how much current it takes to make the horn sound at different sound levels so I don't know how much resistance (when it's supposed to be open circuited) you should be looking for, nor how loud your horn is when it malfunctions.

Then a thorough inspection of the stats and popoff is in order to see that they open when required and are not blocked by debris.

Mark