WESTERBEKE 3M-20A ELECTRICAL SCHEMATIC

[The Shadow Knows]

GUYS,
Having a mechanical/electrical design background, I’m pretty good at troubleshooting but this problem is weird. I turn on the key to preheat glow plugs & start the fuel pump up. I do this for 12 seconds then hit the starter button & she fires right up. I also recently changed out my 10 & 2 micron filters & have fresh fuel in a clean tank so, fuel is knot the problem.

She’ll run 2-3 minutes then the rpm’s slowly falls & she stalls out.
She starts right back up then stalls over-n-over. I put my spare solenoid in but,
the same thing happens. I did a continuity check on the 10 amp circuit breaker leading to the pump and alarm buzzer & all is fine. What I did notice however was that both solenoids felt alittle too warm with engine running so, I hooked the fuel pump up directly to a continuous 12V supply & the engine runs fine with no problems & the solenoid doesn't heat up.

Anyone run into a problem like this? Could there be a problem with the alarm buzzer in the control panel, but I doubt this would cause it to stall. This is frustrating. Here also is the electrical schematic.

Any help is much appreciated guys.

 

[LeslieTroyer]

You are probably not powering the fuel pump when the engine has oil pressure.

The pump runs two times
1) when the glow plugs are on and
2) when you have oil pressure.

Since it starts when you use glow plugs that part of the circuit is ok. Look at the wire between the fuel pump and oil pressure switch - is it in good shape?? Next startup and see if you have 12v at both terminals of the OP switch - if only one terminal it’s a bad switch, if no power at either the problem is upstream of the switch.

 

[Scott T-Bird]

It sounds like you've already diagnosed the problem. Why is it not a faulty preheat solenoid interrupting the lift pump operation? My only question is why do you routinely heat the glow plugs in Florida? I have only rarely pushed the glow plug button, basically only in November in NJ. Is it too warm to heat the glow plugs? The heat may cause loss of current?

 

[The Shadow Knows]

Leslie,

Thanks for your input pal. I did give some thought to OP but my focus was elsewhere.
It will be a few daze, but I'll let you know what I find.

 

[The Shadow Knows]

Scott,

Normally in summer, I don't do it to heat the plugs, but to prime the fuel pump instead.

 

[Scott T-Bird]

I think Les might be on to it between the fuel pump and the oil pressure. I seem to recall another instance were a signal indicating low oil pressure caused the shut down right after starting. But you have normal operating when you provide direct juice to the fuel pump, right?

 

[Scott T-Bird]

Scott,

Normally in summer, I don't do it to heat the plugs, but to prime the fuel pump instead.

Is that normal for your engine or just good practice in general? I don't recall reading that in regard to my Yanmar.

 

[The Shadow Knows]

Scott,

I've been doing it this way since I first put the engine in.
After 12 seconds, I may get a half-crank of the engine & Voila, it's running at idle.
Sometimes if a cold winter day, she may crank twice before starting.

 

[Scott T-Bird]

It sounds like a good idea to prime the fuel pump before hitting the ignition button! Hope you resolve the starting issue. It sounds eerily familiar about the oil pressure. I distinctly remember somebody describing the same symptoms and it turned out to be a bad signal from the oil pressure gauge or perhaps the oil pressure really was low and caused shut down.

 

[Stu Jackson]

Is that normal for your engine or just good practice in general? I don't recall reading that in regard to my Yanmar.

Scott, that's not the issue at all.
First, you have two different engines. Does your Yanmar have glow plugs?
Second, look at the wiring diagram so helpfully posted in the OP. It shows the fuel pump tied to the glow plug solenoid and the oil pressure switch.
This means the pump only comes on when the glow plugs are on (preheat before engine starts) and oil pressure (after engine starts).
"Prime the fuel pump" is actually wrong, 'cuz that's not what the purpose is. The electrical design, which I find amusing at best, turns the pump on, then off, then on again.
The earlier M25 engines had it real simple: IGN on, pump runs. No interconnects with anything else.
The M25XP, M30 and other W engines used this system.
At least the OP knows what he has.

 

[Davidasailor26]

Just to cover all the bases, are you sure that the tank vent is clear? I imagine it might be possible that the vent is somewhat blocked, causing a partial vacuum in the tank after the engine runs for a few minutes. Maybe hot-wiring the pump is enough to overcome such a vacuum and pull fuel anyway. I would not bet that's the problem, but just to make sure maybe run the engine with the fuel fill cap open to confirm.

 

[Rich Stidger]

Make two voltage measurements. First measure the voltage at the lift pump when the glow plugs are energized. You will probably see something around 11.8 to 12.3V. Then right after the engine starts, measure the voltage at the lift pump again. You should see a voltage over 12.3 to 12.6 V.
My bet is that the oil pressure sender is bad and has a high resistance. That would cause the pump to have a low voltage and not pump at full capacity. This oil pressure switch should either be open or closed. Open when there is no pressure and closed when there is pressure.
You can prove this easily by connecting a jumper across the oil pressure sender. That should provide upwards of 12.6V at the lift pump. Then remove the jumper and see if the engine dies. I am betting that it will because the oil pressure sender is bad.
If you check your oil pressure gauge I am confident that you will see good pressure. This system has two oil pressure senders. One drives the oil pressure gauge and the other provides power to the lift pump. Should the pressure drop, the power to the lift pump will be disconnected and the engine will stop.

 

[Mark Maulden]

Stu and Rich has it. This is a bad design. Wire the lift pump to the “key switch” or a dedicated relay from the key switch. Separate the lift pump from all the oil stuff..

 

[The Shadow Knows]

Leslie, Stu, David, & Rich,

There is no problem with fuel vent/flow rather, it's on to checking The OP switch.
If I bypass this & power the fuel pump directly to 12V, the engine runs fine.
I just hadn't thought to look at the OP as maybe causing the problem. It's on my list for tomorrow.

But I wanted to thank you all for your input.

 

[RitSim]

I had a similar situation on my Westerbeke 42, but the problem was not electrical. I temporarily inserted a piece of clear tubing into the discharge of the lift pump. Almost all of my hose and piping joints were allowing air to be sucked in. In addition, I had changed my fuel filter body and there was a ball check that was the final culprit in choking the fuel flow.

 

[The Shadow Knows]

RI,

I've checked all my fuel line connections & I have every hose connection on my boat be it water,
fuel etc. double clamped. But, if the pump runs fine without the connection to what
might be a bad OP switch is causing this as I go down the line of troubleshooting.

But you found your problem, as it always takes thorough checking to find the culprit.