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testing lift pump on 94 6.5

16K views 13 replies 6 participants last post by  efren 
#1 ·
i got a 94 deisel 3500 i was reading the newbie thing anyways went to check the lift pump operation, the pump on the 94 does not prerun with the glowplogs apparently, so i had the engine running i cracked open the t valve for about 3 seconds fuel poured out of it and the engine did not burp or stutter it never missed a beat..... did i have the valve open long enough? and does this mean my lift pump works?
 
#2 · (Edited)
If you get fuel with the engine running and it does not stall right away I suspect that the LP is working.
A better test would be to hook a fuel presure gauge to the line connected to the tee-valve and check running pressure-that will tell you for certain if there is pressure at that point and how your lift pump is working.
 
#3 ·
94-95, the lift pump will NEVER pre-run. It is like that from factory. Nothing to worry about. You can mod it such as Kennedy LP/OPS harness will pre-run with key "on".

In this same year, the OPS controls the LP during engine run. So bad OPS can cause LP not to run. This is the part of the OPS which controls the LP not the one to the gauge.
 
#4 ·
In addition, from your description, you have a good running LP and OPS.

Unless you have other symptoms, just enjoy your truck. Worry about it when something is not right.
 
#7 ·
Oil Pressure Switch/sending unit. It gives the reading on the dash as well as controls the flow of current to the lift pump.

Check through the FAQ's at the top of this forum for a complete list and other helpful info.
 
#10 ·
#11 ·
I bought a 12v relay, and an 'Add a Fuse" and now my lift pump runs when the key is switched to run.
 
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