I have a Universal M-25XPB engine. Last year the wire for the oil pressure switch broke off. Not realizing the problem, I was still able to run the engine with no problems. Finally on a cruise the engine stalled. After being towed to a marina a mechanic repaired the broken wire. He explained that the oil pressure switch actuates the fuel pump. When I turned the engine key on I could hear the pump clicking. He claimed I was able to run the engine without the pump activating since gravity delivered the fuel. I had a full tank. When the tank was less than halve full gravity was not able to do the trick hence the stall. Now finally my question. Now,I do not hear the fuel pump clicking when I turn the key. Is this caused by a full tank and hence the fuel pump does not need to be activated? Or is the fuel pump always activated when the engine key is turned on?
fuel pump
- Thread starter insamji1
- Start date
- Status
The fuel pump will run and make a clicking sound if either of these 2 conditions exist.
1) The key switch is held in the spring loaded position (activating the glow clips as well).
2) After the engine starts and the oil pressure switch closes.
Note: you should hear the buzzer sound continuously when you first turn the start switch to the on position, (not the spring loaded position). The buzzer circuit is getting it's ground when the motor is not running from the + 12 side of the fuel pump, yep, the + 12 side. This is because the coil that runs the fuel pump is low enough resistance to provide a stiff enough ground for the buzzer to sound when it is not energized. Once it energizes them the buzzer shuts off because it now has +12v for it's ground connection, no potential difference from +12-+12 so it won't sound.
This feature is a good check to let the operator know that the fuel pump is at least in the circuit and likely to function. There is a shovel connector on a pig tail that provides the + 12 connection to the fuel pump located on top of the the pump, it corrodes in this acrid environment and then will not pass current. The engine will gravity feed until ~5/8 of a tank running on the level. After that it will start loosing power and then crap out from fuel starvation.
So, if you don't hear the buzzer when you turn the key on, than check this connector.
1) The key switch is held in the spring loaded position (activating the glow clips as well).
2) After the engine starts and the oil pressure switch closes.
Note: you should hear the buzzer sound continuously when you first turn the start switch to the on position, (not the spring loaded position). The buzzer circuit is getting it's ground when the motor is not running from the + 12 side of the fuel pump, yep, the + 12 side. This is because the coil that runs the fuel pump is low enough resistance to provide a stiff enough ground for the buzzer to sound when it is not energized. Once it energizes them the buzzer shuts off because it now has +12v for it's ground connection, no potential difference from +12-+12 so it won't sound.
This feature is a good check to let the operator know that the fuel pump is at least in the circuit and likely to function. There is a shovel connector on a pig tail that provides the + 12 connection to the fuel pump located on top of the the pump, it corrodes in this acrid environment and then will not pass current. The engine will gravity feed until ~5/8 of a tank running on the level. After that it will start loosing power and then crap out from fuel starvation.
So, if you don't hear the buzzer when you turn the key on, than check this connector.
Thanks for the information. I will check out the connection, since I am not getting a buzzer sound.
Witzend is right. You should check the wiring diagrams in your manuals. The fuel pump runs when the glow plugs are on and when the oil pressure switch closes once the engine gets going.
A detailed discussion starts on page 4, here: http://c34.org/bbs/index.php/topic,3347.45.html
A detailed discussion starts on page 4, here: http://c34.org/bbs/index.php/topic,3347.45.html
- Status