Merc 175 - total loss of power

[customfab]

So I was out today cruising the lake when suddenly the boat lost power. It never died but lost a bunch of power. For a second I thought maybe it was running out of gas. Turns out the tank is full. So I ran the boat slowly back to the dock (about a 20 min ride). It idles perfectly and had so problems starting. Almost as if the boat was running off just a few cylinders.

Thoughts?

 

[Mark]

Unfortunately it could be a dozen different things. Start with the simplest three first.
1) Check the plugs, are they fouled? Do you use new plugs every spring?
2) Check for water in the gas. Motors run crappy on water.
3) Dirt in the filter or fuel restriction in line?

Then you go dig deeper;
4) Does your fuel tank have an anti-syphon valve? Remove it?
5) Fuel pump diaphram shot? Replace.
6)Crud in carbs? Clean or rebuild.

The electrical side is tougher to test and requires a DVA meter. Bad Stator, bad trigger, bad switch box, bad coil etc.
My best advice is order a service manual for that motor from your dealer. They have the perscribed troubleshooting protocol for each problem. The hit and miss approach almost never works.

 

[ross]

that about sums it up mark

 

[customfab]

Unfortunately it could be a dozen different things. Start with the simplest three first.
1) Check the plugs, are they fouled? Do you use new plugs every spring?
2) Check for water in the gas. Motors run crappy on water.
3) Dirt in the filter or fuel restriction in line?

Then you go dig deeper;
4) Does your fuel tank have an anti-syphon valve? Remove it?
5) Fuel pump diaphram shot? Replace.
6)Crud in carbs? Clean or rebuild.

The electrical side is tougher to test and requires a DVA meter. Bad Stator, bad trigger, bad switch box, bad coil etc.
My best advice is order a service manual for that motor from your dealer. They have the perscribed troubleshooting protocol for each problem. The hit and miss approach almost never works.

Yeah, thanks. Boat is extremely well kept. Regular gas every week.

Plugs replaced last year. I will check them but they were ok 2 weeks ago.

Don't know about any anti-sphyon valve. Easy to see inline near the tank?

I have a feeling this is eletrical related. Boat instantaneously lost a majority of power. Not intermittent signs or anything. Instant. Thinking maybe a coil pack went bad. Guess I'll start with your list so thanks.

 

[illMATTic]

did you ever try to run the boat again? did you try to run it fast just before you put it away? i am wondering if it was just a fuel delivery issue when running higher rpm's.

 

[LAPLANT]

DON'T FORGET TO RUN A COMPRESSON TEST

 

[Mark]

Actually there is one fairly simple test. Bring idle to 2000 rpm. Pull one plug wire at a time using gloves and insulated pliers. The RPM should drop sliightly each time. If it does not then that is culprit. If it is just one cylinder it could be a coil. (you can switch the leads and plug wire to a different cylinder and see if the problem moves with it.) If it is two it could be the trigger or switch box. If it is three it is probably a switch box. Then there is you stator as well. At this pont if it is not a coil or plug you will probably need the DVA. You don't want to just start swapping parts unless you have extras lying around. It is a very expensive way to diagnose a problem. Usually we leave that approach to the marina mechanics.

 

[familyboat]

I have a 1993 mercury 175 it did the same thing last week while we were at the lake.
I replaced stator and fuel diaphragm before realizing it was the fuel "bulb" had gone bad. The check valve on the bulb was leaking and getting air into the fuel line. So it would idle fine, but as you tried to give it gas it would bog because it was getting air in the line.

I hope this helps, this was my problem.

 

[customfab]

So I was out today cruising the lake when suddenly the boat lost power. It never died but lost a bunch of power. For a second I thought maybe it was running out of gas. Turns out the tank is full. So I ran the boat slowly back to the dock (about a 20 min ride). It idles perfectly and had so problems starting. Almost as if the boat was running off just a few cylinders.

Thoughts?

Thanks for all the input. I forgot to provide updates from long ago. Boat is back to running excellent. Plugs needed changing and a few of the leads turned out to have non-secure conditions. I think I pumped them with the motor cowl. Easy fix.