Lift Pump Failure Analysis

[EScott]

Any of you guys who have had lift pumps go south take 'em apart?



I changed out mine yesterday and having a lift pump that does what it supposed to really helps with the grin factor. For addtional grins I decided to take the pump apart. I wish I had a digital camera because describing this is going to be tough but...



I removed the plate at the top of the pump and the first thing that I noticed was that the impeller was NOT centered in the pump housing! I removed the impeller and looked at the shaft coming up from the motor, and it was so far off center that the shaft was actually rubbing on the side of the housing!!!



Anyone else see anything like this?

 

[TKilgore]

Off Centered

I posted a couple months back when I changed mine and it looked as you described. My shaft was actually against the housing. I was told they are built off center,and alot of pumps are, but I don't know why given the location of the inlet and outlet port. All I know is my new one does better, wish I had taken the top off it.



Tom

 

[Mopar-muscle]

yes they are built that way , its a sliding vane , and inorder to get the space for the vanes to slide out it has to be that way ...

 

[EScott]

Ok so I realize that it's a sliding vane, but I have never seen one where the "hub" was actually rubbing on the inside of the housing. How can there be room for the vanes to move to the outside when half of the rotation the hub is against the housing. Seems to me it would cut pump ability in half?



I seriously got half a brain to pull the new pump and inspect it...

 

[icarus33]

Here's the photos I took from my disection.



ic

 

[hammersley]

How Long does it take to change a lift Pump?????

About how long does it take to change the beast... .

 

[jjohnson1177]

On my 2001 it took about a hour and that was with pulling the top off of the old one to see why it was weak. Other then some wear on the vains nothing seemed to be wrong. The new pump sure works great though.

 

[Vaughn MacKenzie]

E-Scott, the center portion has to be right smack against the side of the chamber for a suction pump to work properly. Those vanes are thrown outward by centrifugal force when the pump is running and that is how each little section between the vanes can "seal" against the side and be able to "pump" the fuel in and out of the chamber as it changes size.



Vaughn

 

[EScott]

Originally posted by Vaughn MacKenzie

E-Scott, the center portion has to be right smack against the side of the chamber for a suction pump to work properly. Those vanes are thrown outward by centrifugal force when the pump is running and that is how each little section between the vanes can "seal" against the side and be able to "pump" the fuel in and out of the chamber as it changes size.



Vaughn

Ok, but should the two parts be scoring each other? I would say that close would be ok, but gouging each other is a whole 'nother rodeo...

 

[THerman]

Ok, but should the two parts be scoring each other? I would say that close would be ok, but gouging each other is a whole 'nother rodeo... [/B][/QUOTE]



The hub of the vane pump must be VERY close to the wall (as close as they are to the side plates!)



The way vane pumps work is that the empty volume(between vanes) increase over the inlet port (sucking in the fuel) and then decreases in volume over the oulet port (pumping out the fuel) The starting volume should be as close to zero as possible for best efficiency. The pumping rate is a function of rpm of the pump and the max change in volume... the amount of pressure the pump can produce is a function of the sealing ability of the vanes(on all three sides) and side sealing of the hub... leakage at these points lowers pump oulet pressure. These sealing surfaces are usually where the problems lie.