Mercury 150 Black Max Lacks Power

[orlwind]

I have a Mercury 150 HP Oil Injected Black Max Serial Number 6608229 on a 20 foot Wellcraft. I think the engine is about a 1985 or 1986 model year but I am not sure. I don't see this number on the listings of Mercury serial numbers.

Here is the problem
When not under load, It seems to run fine and will accelerate in rpm. However, when under load (in gear and in the water), it will not accelerate properly and lacks power -- it won't power the boat past about 10 or 15 mph. Normally this engine will push my boat at 40 to 45 mph.

Also, occasionally, when not in gear and I increase the RPM, I get a beep...beep...beep noise that stops when the RPM is reduced. What does this sound mean? Is there some kind of RPM limiter that is engaging to prevent engine damage?

I have checked the plugs and all appear to be getting ample oil. In fact, it seems to be running a little rich as there is more smoke than normal at startup.

I checked the compression and the spark for each cylinder. Here are the results.

Cylinder Compression Spark
#1 115 PSI Yes (But not as strong as Cylinders 2, 4 & 6)
#2 128 PSI Yes (Strong Spark)
#3 115 PSI Yes (But not as strong as Cylinders 2, 4 & 6)
#4 123 PSI Yes (Strong Spark)
#5 118 PSI Yes (But not as strong as Cylinders 2, 4 & 6)
#6 124 PSI Yes (Strong Spark)

Because cylinders 1,3 and 5 seem to have a poor spark, I am thinking that either the Stator or the power pack are bad.

Can you provide advice on what the problem may be and how to diagnose the specific problem?

Thanks!

 

[Chris1956]

Re: Mercury 150 Black Max Lacks Power

It can clearly be stator or power pack. How do you know the spark is weak? You can swap powerpacks(you should have two PPs on that motor) and see if the problem moves.

 

[Laddies]

Re: Mercury 150 Black Max Lacks Power

Just swap the red with the red/white and the blue and the blue/white if problem moves it's the stator and if it don't it's the box.

 

[orlwind]

Re: Mercury 150 Black Max Lacks Power

Thanks! I will give that a try.

 

[j_martin]

Re: Mercury 150 Black Max Lacks Power

The beep -beep-beep you hear is the oil alert. It get's information that the engine is running from #2 spark plug (the green primary wire). That's another indication that #2 is not firing.

If you move that wire form the oil alert module to any terminal on the other switch box, the beeping would stop, but it still would not run right.

If you do the stator lead switch as recommended above, the beeping will stop if the stator was the problem. It will continue to beep if the switchbox is bad.

Yer looking at a switchbox (power pack) or stator as the guys above said.

hope it helps
John