Engine/Transmission (1998.5 - 2002) WHAT fails on the lift pump??

[merryman]

After suffering an intermitant lift pump failure, today I took the OEM apart. It seems to be a heavy, well built pump, and I coud find nothing wrong with it except aht in innards were quite wet with what looked and smelled like diesel.

/wires were in place and looked OK,

Brushes and armature looked good,

The little "vanes" all seemed to be in place and free without apparent damage.

So what was the failure???

Could a failed seal that allowed diesel into the pump electrical components cause a failure?

In may case, pressure went to zero,followed in just seconds by the engine faltering and missing. On restarting it would run fine, the first couple times for about 15 miles, then one time it started and ran very pooly, the last time after sitting for a couple hours it started and ran fine with good pressure (15 idle, 12 cruising +-), the started faltering and barely running.

I would appreciate ideas,

I would also like to hear details of any complete pump relocations.



Vaughn

 

[WadePatton]

Somewhere in the million or two LP threads I've read, I remember there being more than one type of failure. I'll let those who, like you, have cut the little suckers open give you those details. My weak, but functional LP is out in the garage intact.

 

[isb360]

I haven't pulled an LP apart yet, but if it's a brushed motor, failure could come from worn brushes. As brushes wear and spring pressure on the armature decreases, resistance increases and current flowing to the armature (translating to torque on the shaft) decreases as well. That could be why there is a gradual degradation in performance as motor brushes wear out. Separately, there is probably a spec somewhere on motor winding coil resistance. As a motor is used and the insulation goes through heat/cold cycles on the motor windings, it will break down. Depending on the location of breakdown, the effective winding length will decrease, providing a weaker magnetic field for the armature, therefore less current, etc.



What I am getting at is that although it appears healthy, further diagnostics would be required, compared to specifications, to determine root cause of failure.

 

[rweis]

LP = $133, VP = $1200, I'd replace it if it even whimpers once. Then you can test and check until you are satisfied you have found the cause.



Bob Weis

 

[Turbo Tim 1]

I hate to say it, but here is a link to a very good post from an ex-TDR member who moved over to the DTR and is now an ex-DTR member, not sure where he is now but I am sure he is arguing with someone. People just don't seem to get along with Gary, I guess they all have problems.



Anatomy of a lift pump

 

[merryman]

After reading a BUNCH of post, especially some threads Gary put my onto, I learned enough about the "guts" of the lift pump to figure out that the "ball" in the regulator portions was just not there!!

Wonder if it was in the filter? Or maybe I just let it fall out as I disasembled it, but that appears to be the cause of my failure.



Vaughn