79 300td - relationship between primer pump and lift pump function?
 

Hi:

If the hand primer pump leaks with use and is difficult (but not impossible) to close without some leakage, does this indicate that the lift pump itself is also not functioning well?

It was my impression that the hand pumps fail all the time, but that the lift pumps rarely do.

Thanks to all who offer an opinion,

Brad

No. But any leakage from the primer pump is a problem.

Thanks. In what way?
 

If the leakage is temporary, can there then be subsequent ways that it affects how the car runs?

On the Old Style Hand Prime with the shiny Aluminum body there is a seal at the Bottom. When you push the Knob all the way down and you screw it down snug that seal is supposed to prevent air from leaking in. It is possible for the bottom seal to be good and for it to leak when you pump it up and down. However, a Hand Primer that is leaking out of top of the Aluminum tube is on borrowed time.

To make it simple the Hand Primer sits between the Inlet Valve and the Outlet Valve and with the exception of being a possible source of an Air leak The Hand Primer does not effect the performance of the Lift/Fuel Supply Pump.

Thanks.
 

I appreciate the clarity.

No they don't fail all the time. They fail after 25-30 years; so many cars with the original primer pumps will likely have issues sooner than later.

the question is misleading.

I agree with tango; the LP performance can be effected by the leak, but the LP mechanisms work independently of the hand primer.