Engine/Transmission (1994 - 1998) Is Lift Pump My Bad?

[Jeff H]

Well lately I've noticed some loss of power. I use to be able to slip the clutch easily. Now it don't slip and feels slugish.

My normal reading for lift pump psi were.

20 psi idle 750 rpm.

31 psi 2000 rpm.

My latest reading as of now.

5-8 at idle 750 rpm

15 to 19 psi at 2000 rpm.

When I start up the truck its at 0 for about 3 to 5 secounds and run rough. Pressure builds very slowly even up to 2000 rpm.

I streched out the spring on the over flow valve a little. . 055

No change.

I checked the prescreen fuel heater. Had a slight leek again. Was very clean on the inside.

I have 217,000 miles on the origanal lift pump and over flow valve.

What your thought?

Thanks

Jeff H.

 

[Joe G.]

It sounds like an air leak prior to the lift pump to me. Mine did the same thing. It turned out to be the fuel heater electrical connecton. Another guy had a bad fitting where the steel fuel line connected to the fuel heater. It also could be the supply fuel hose or a gasket in the fuel heater/prescreen assembly.

 

[JohnE]

Jeff

You fought the leaking fuel heater a couple times. Maybe back again?



How about the elbow hose between heater and lift pump.



What was the pressure when you checked it at Mike's in January?

 

[Jeff H]

I did have some leaking some where around the preheater. Also have oil or fuel running down the side of the engine down to the oil pan. Starts in the lift pump preheater erea. Not easy to see exactly where it starts. Electrical connection looks dry. Will disconect it tomarow and inspect.

I pulled the heater bowl off. Cleaned it and reinstalled it. After that is when it started to run rough.

I have had problems last year with the preheater. Never really lost any power due to it. Fuel coming out of the electrical connections.

Might try and pinch off the return line tomarow to see if it will build any pressure.

 

[Joe G.]

Jeff,



If fuel is running down the fuel heater/pre-filter then it's sucking air for sure. You might try removing the heater and see what happens. Do this by removing the pre-filter on the bottom. Then unplug the wireing harness that goes to the heater from the engine wiring harness. Use an 8mm allen wrench to remove the shiny screw the holds the black plastic heater. Becareful of the O-ring type gaskets. Put the shiny screw, heater, short harness, and one of the gaskets on your work bench. Reinstall the pre-filter. While you are at it check to see if the input fitting on top of the heater/filter assembly is tight and in good shape. After it's all back together, start and check for leaks. If no fuel is dripping take it for a drive.

 

[Jeff H]

Well I hope its not the preheater? But today I checked a few thing out. I started up the truck and opened the bleed screw for a few secounds. I then checked the pressure again. Now the pressure is about normal again. A tadd higher. But I think that had to do streching the spring in the ov valve.

I geuss there must have been a lot of air in the line. Pulling the heater bowl off. Some of the fuel must have drained back to the tank. Then what ever drained out of the line to the filter. But will have to keep en eye on the preheater for leaks yet. I'm about ready to yank that darn thing for good. Plenty of after market fuel heaters out there.

 

[Joe G.]

Just remove the hockey puck shaped thing that is the fuel heater and put it back together for a test. It takes less than five minutes to do that. A 17mm socket and an 8mm allen wrench is all the tools you need.