Does Fuel Pump Only Run When Needed?

[Urantian]

I discovered that the fuel pump on my M35A2 was not running. There was 24v on the plug which connects over the pump. However, the pin inside the receptacle had no continuity with the fuse inside. There was evidence of electrical issues inside the housing, and the in-line fuse had been replaced with a small metal bar. I found that if I connected the wire from the pump directly to the plug, the pump worked. After letting it run for a minute, the truck started right up, much more easily than usual. However, after shutting down, I found that the pump was not running. Does the pump have a pressure sensor, so it only runs when needed?

Thank you.

 

[NY Tom]

Normally the in tank pump runs all the time that the main power switch is on. Not needed to run the engine - but starts much easier with it running.

 

[Urantian]

Thank you. When you say "normally", does that mean it might be off sometimes? I'm not sure whether it died after a short while, or it's not needed. I understand the pump is only needed for starting.

 

[NY Tom]

It will only be off if the main power switch is turned OFF or you have an electrical connection problem. Otherwise it will run all the time. Doesn't hurt anything to have it running - just shortens the life of the pump by some amount.