Low-pressure fuel pump activation

Pete G · May 19, 2025, 12:35:20 PM

I rewired my boat to address the "critical upgrade" issue. I'm not able to start the engine. When I turn on the batteries, I hear the low-pressure pump activate. Do I have this wired incorrectly? Should it only turn on when I'm cranking the engine over?

Ted Pounds · May 19, 2025, 02:30:06 PM

It should always be on to ensure fuel is flowing from the tank....

Ron Hill · May 19, 2025, 03:16:45 PM

Pete : The electric fuel pump is wired into the key switch and when that switch is ON the fuel pump keeps running so that fuel is at the injector pump. Like Ted said - it always is running.

Most fuel tanks are not higher than the engine (C34 is an exception) so that's why the pump is always ON!!

A few thoughts

Pete G · May 19, 2025, 04:00:07 PM

I've been struggling with a fueling issue to the injectors. I cannot get fuel flow through the high pressure pump. I tried replacing the pump with another one, but no change. I can see the fuel cam turn with the pump out when turning the engine by hand. I've bled the system at the fuel filter, and then at the fuel rail.

Maybe I didn't have the boat at TDC? I'm out of ideas and my yard has neglected my boat. Maybe the glow plugs?

Jon W · May 19, 2025, 07:09:53 PM

It did run and now it doesn't?

Pete G · May 20, 2025, 04:59:15 AM

Quote from: Jon W on May 19, 2025, 07:09:53 PMIt did run and now it doesn't?

Yes. It ran after the wiring change. I let it run for a minute, and then when I came back to put in, it wouldn't start.

Jon W · May 20, 2025, 07:29:22 AM

Do you still have a M25XP in your 1987? It ran after the wiring change, so that's not the problem. When you replaced the high pressure pump did you verify the timing of the pump is correct? Did it run after replacing the high pressure pump? I have individual tubes from the pump to the injectors. Is that what you mean by fuel rail? Is there fuel to the pump, but not after the pump? What does "when I came back to put in, it wouldn't start" mean? Hopefully others chime in to help you troubleshoot.

Pete G · May 20, 2025, 11:13:59 AM

I am not sure about the timing - I'm going to revisit to make sure I was at TDC when I installed the new pump, but even if I was off, I would still expect some fuel to be pushed through the pump. Yes, by fuel rail, I mean the 3 metal fuel tubes.

waughoo · May 20, 2025, 12:07:58 PM

so... even if you were off on TDC, you would see fuel at the injectors via the hard piping, but only if you were cranking the engine. They won't spit fuel with just the electric pump on itself. The electric pump will deliver fuel to the injection pump, but not through the injection pump.

Hard to say from this far away, but I suspect you need to turn the engine over more with the injector nuts cracked off. I would try only one injector nut at a time until you get fuel there. You should only run the starter for about 10-15 seconds and then give it a rest for about the same amount of time. I'd try that for each injector nut until you get fuel at the injector. You might still be out of time on the injection pump, but regardless should see fuel delivered to the pipes.

Jim Hardesty · May 20, 2025, 01:55:53 PM

QuoteYou should only run the starter for about 10-15 seconds and then give it a rest for about the same amount of time.

Also, if a lot of cranking, maybe about 2 minutes total, drain the muffler. Without exhaust pressure, water can enter the engine.
Jim

Ron Hill · May 20, 2025, 06:12:06 PM

Pete : The timing of the injection pump is set by the shim/shims that are between the pump and the engine. What were the instructions that came with the new pump?? TDC of which piston??

A few thoughts

Jon W · May 20, 2025, 08:35:06 PM

Pete, still trying to get a picture of what you're facing.
Do you have a M25XP?

You say you bled the system at the fuel filter, and the fuel rail. Did you get fuel exiting the fuel filter and fuel rail?

Pete G · May 21, 2025, 06:06:43 AM

I tried that with the line open at the injector, not the pump, so I'll try that this weekend. I won't be able to see the fuel spurt out, but I'll be able to see the evidence.

Pete G · May 21, 2025, 06:08:18 AM

Quote from: Jon W on May 20, 2025, 08:35:06 PMPete, still trying to get a picture of what you're facing.
Do you have a M25XP?

You say you bled the system at the fuel filter, and the fuel rail. Did you get fuel exiting the fuel filter and fuel rail?

I get fuel to the filter, and I get fuel to the high pressure pump. I get fuel flowing through the bypass/return line. It does not exit the high pressure pump - at least at the end of the metal line - checking with the line removed next.

Pete G · May 21, 2025, 06:09:43 AM

Quote from: Jim Hardesty on May 20, 2025, 01:55:53 PM
QuoteYou should only run the starter for about 10-15 seconds and then give it a rest for about the same amount of time.

Also, if a lot of cranking, maybe about 2 minutes total, drain the muffler. Without exhaust pressure, water can enter the engine.
Jim

The boat's still on the hard. How does one drain a muffler?