Lift Pump Problem

[Shermanator31660]

So I've narrowed my lack of fuel delivery down to the lower lift pump on the F150. It barely shows any vacuum at all on the inlet port and shows zero pressure on the outlet port. So my question is, which part is faulty, the rubber diaphragm, the small ports that are fixed in place in the valve body, or the gasket on the outer cover. There are rebuild kits for these pumps but I'd rather buy the right part rather than all the guts. It hasn't been bleeding gas into the motor so I don't know if that would eliminate the rubber gasket as the culprit or not. The pump on my 8 Yammy went and it was the rubber diaphragm but it also bleed gas into the motor. Also, any reason there couldn't be a low pressure electric lift pump doing this job rather than the two mechanical pumps???? Sherm

 

[99yam40]

lift pumps do not last forever, replace with new ones and go enjoy the water

 

[Shermanator31660]

If life were that easy I'd be in a different world, at $400 here for a pump in Canada I'd rather figure out which part is hooped rather than replace entire unit, I believe that's why they have rebuild kits, but thanks! Sherm

 

[99yam40]

did not realize they were so much money
definitely not like the old 2 stroke lift pumps

still with a diaphragm and check valves there should not be much that can go wrong if there is proper driving force to make it work

I take it these still run off of some kind of pulse, but not sure from what

If the other one works fine you might try swapping them if they are the same, to see if it makes a difference

 

[Shermanator31660]

I have a pretty good idea which one if FUBAR'd and I've just isolated the bad one by disconnecting the plugging fuel lines, the good one runs fine and shows fuel pressure on my GPH gauge. I was going to leave the bad one disconnected and see if I could just operate on the one lift pump but my local mechanic advised against it, stating that you could cause damage to the small movable vents in the body area, due to them not getting any fuel over them for lubrications, makes sense. I also asked him about going to an electric pump rather than the mechanical, he also advised against that as the mechanicals are much more reliable, or at least the electric fuel pumps that are not cooled by being submerged in fuel such as the high pressure pump in the VST tank. Any fuel pump that simply has fuel run through it is prone to overheating, and that could be why Yamaha has stuck to the type of lift pumps they have. Anyways, I have a new diaphragm on order so will replace the one in the "bad" pump and hopefully it'll be fixed. I still use the motor though, just have to make sure to prime the bulb up before launching! Sherm