Engine/Transmission (1998.5 - 2002) Lift pump plastic motor coupling

[15w40]

I have been reading a lot of posts about “fixing” the lift pump problem, and adding a filter before the lift pump. One mode of failure has been with the plastic coupler that connects the electric motor to the pump rotor. I had assumed that if the pump inhaled some trash along with the fuel the rotor could jam and the motor would then break the fragile coupling. I was wrong.



The Carter pump has an inlet screen that will filter particles down to about 600 uM (microns). The pump inside the volute has a clearance greater than 700 uM. It seems to me that there has to be another reason for the motor coupling breaking. I wonder if the failure of the coupling is due to fuel gelling in cold temperatures? If it is then mounting a Carter pump back by the tank, away from engine heat may be a problem.



Here is a photo of the pump volute, rotor and vanes. The smallest gap measures 0. 030” or 762 uM, too large for trash to jam. This pump has about 70K miles on it and the machining marks are still visible. The plastic coupler is still in good shape as well. What failed on this pump was the infamous spillover valve spring.



What I find interesting in this photo is the “+” sign in the middle of the rotor. It took me a while to see that it is used to channel fuel from behind the vane on the output side to the input side vane. This hydraulic pressure in combination with the centripetal force of the spinning rotor keeps the vanes pressed against the volute wall.



Still pondering the mysteries of lift pumps …

 

[Steve St.Laurent]

Well, my truck has been through 2 winters with the carter pusher pump by the tank. This winter was veeeeeeery cold too. My truck was parked outside all winter and through a lot of it wasn't plugged in (block heater had failed). No problems with it yet.

 

[Ncostello]

Too bad the rotor connection isn't simply metal and molded into the rotor during manufacturing. I cant even tell how they get that plastic thing in there... press fit perhaps. I was trying to figure out how to get something in there if mine breaks. Wonder if Carter would sell individual replacement rotors?