89 Merc Black Max issues

[lunacyfringe129]

hey guys...im new to the forum. I am a proud owner of a 1989 merc black max 150. Its a great engine, but yesterday I was out cruising and the engine was running great, until it decided to die on me out in the middle of the lake at around 3500rpm. I was just cruising around the lake, not even working the engine hard. It sputtered and stalled out, and when I tried to start it again, the starter wasnt able to crank it over, almost like the pistons had seized.It had cooling water and oil, and the block wasn't hot, so I knew it hadn't overheated. But what got me was when I tried to start it 5 mins after. It started right up, but was missing really bad. I was just happy to have it running again, and it got me back to the dock. The entire way back it was missing really bad, but was able to keep the boat up on plane. I don't really know where to start on this diagnosis. I checked the plugs, and they are all fine, and the engine once again starts and runs perfect. Some guys are telling me that there could be short in the ignition somewhere, but why would that cause the engine to not crank over for 5 mins? If you guys could give me some insight on where to look, or even just some info on if this has happened to you before, I'd really appreciate it.

Thanks, Tyler

 

[LubeDude]

Re: 89 Merc Black Max issues

When you checked the plugs was there anything on them that resembled aluminum?

If not then your next course of action would be a compression test. If they are around 120 and within 5% of each other then move on to ignition.

 

[OldMercsRule]

Re: 89 Merc Black Max issues

Hi Tyler, The failer to turn over and then the ability to turn five minutes later sounds like a heat related problem to me. (Something seemed to increase resistance for the starter, assuming the solenoid clicked and the starter engaged the flywheel but would not crank it.) I am assuming your battery is strong, well charged and the electrical connections are clean and tight. Could there be water in your fuel, or are you running an alcohol blend that has picked up some water, or just maybe a bad tank of gas? I think that could explain the engine quitting @ 3500 and running rough, back to the dock. Partially plugged fuel filters, and or a weak fuel pump could be related to this problem as well. The starter issue seems like the real mystery here, and may be an unrelated electrical bug that picked on you at the same time the engine sputtered. JR

 

[Texasmark]

Re: 89 Merc Black Max issues

Couple of things.

Boy son has a 95 150 so they are probably the same critter. Each bank of cylinders has a thermostat which is located at the top of the water jacket and has a 3/8" rubber hose coming from it's cover. I don't think this engine has a bypass valve (which opens at high rpm/s or high input water pressure encountered when "ram" water is present).

So, if a thermostat sticks closed, or fails to open for whatever reason there is no fresh water getting to the heads and they, and their respective cylinders, can overheat.

About midway down the rear of the heads should be a brown (brown/blue) wire coming out which is connected to the overtemp sensor; one on each bank of 3 cylinders. If the engine experiences a stuck stat, (opens at 143F on his) the respective switch should close (195F) and generate a constant tone on the audible alarm or constant light if so equipped.

If you overheated and had no functioning alarm, you experienced a siezure from overheating. BTDT

The fact that you were able to get it started tells me that you cooled enough for the pistons to again move in the cylinders but the missing says that you damaged something.

Like Lube said, check the plugs closely for metallic particles and while your plugs are out observe the cylinder walls for scoring/scratches/galling indicating that the piston got hot and expanded to the point where the skirt was dragging on the cylinder. Alum on alum spells galling (chunks of alum sitcking to the other alum surface).

If that happened you are in for an overhaul and the more you run it the more you are going to score the cylinders and may prevent an overbore which would require a new block.

In my situation I was "green" to this engine and thermostats in general in outboards and all, and mine was going bad. I sensed that the engine was doing funny things but had no idea what was doing it. Had the same 5 or so minute senario you had but still didn't put 2 and 2 together. Then one day it finally froze when I was at wot and brought the boat to an abrupt stop, I assure you. Then reminissing, all the "funnies" added up.

Cost me $1000 for the powerhead overhaul, bored .030 over, new pistons and all; I did the rest of the work.

Good luck.

Mark

 

[KCLOST]

Re: 89 Merc Black Max issues

Texas could be right...

But there is also the possiblity that one of both of your switchboxes are bad.....
But the inability of the engine to turn over at all does not sound good... First check the compression, and spray some fogging oil in the cylinders before you do it...

Second, check the spark on each cylinder and let us know....

 

[ozziebob]

Re: 89 Merc Black Max issues

switch box my ass! Let's think about this. All of a sudden the motor experiences two intermittant faults. Not likely! THE Problems have to be relateded. Check your overheat warning system first. Compression test your engine and if both are O.K lets looks towards faulty power supply! Eg. bad connectors, wiring harness

 

[Capt Ken]

Re: 89 Merc Black Max issues

You leaned out a cylinder and burnt a cylinder. You will find one cylinder with zero compression.

 

[LubeDude]

Re: 89 Merc Black Max issues

You leaned out a cylinder and burnt a cylinder. You will find one cylinder with zero compression.

Like I said in the beginning, start with a compression test then move to electronics, doesn`t sound electrical to me.