• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Lift Pump Not Working, Where to Start

Will L.

Well-Known Member
Messages
14,394
Reaction score
22,042
Location
Boulder City Nv
Remove the fuel shut off solenoid and try again.
that fuel should be flowing through the ip, and it isn’t.

If that doesn’t let it flow, screw it back in.
Remove incoming fuel line, use rubber tipped air blower from air compressor set at 20psi, and blow air through while cranking for 20 seconds. Then hook back up remote fuel line and try again.

keep that fuel return line disconnected the entire time.

And Did you loose my number? Shoot a text to a couple folks if we aint answering while your wrenching and stuck. Sheesh.
 

Big T

Well-Known Member
Messages
6,276
Reaction score
8,813
Location
Fullerton, CA
Remove the fuel shut off solenoid and try again.
that fuel should be flowing through the ip, and it isn’t.

If that doesn’t let it flow, screw it back in.
Remove incoming fuel line, use rubber tipped air blower from air compressor set at 20psi, and blow air through while cranking for 20 seconds. Then hook back up remote fuel line and try again.

keep that fuel return line disconnected the entire time.

And Did you loose my number? Shoot a text to a couple folks if we aint answering while your wrenching and stuck. Sheesh.
After you said 6 psi dead head pressure was insufficient, I'm installing the Walbro FRC-10 to eliminate all doubt. Had already purchased the Walbro when Leroy was first pushing it.
 

Big T

Well-Known Member
Messages
6,276
Reaction score
8,813
Location
Fullerton, CA
So did you ever get this running?
Nope. Had to leave back to Montana.

No change in fuel coming out the return line side of the IP. Did not have time with 2nd person to operate starter so I could check pressure before IP or pull the fuel shut off solenoid to check fuel there. LP was working as I could hear it. I think the theories of clogged return line to tank is hogwash because it’s not coming through the IP. Likely back down in October or November. I was also busy working on wife’s 4Runner which takes higher priority as it is her daily driver, while this ‘94 Suburban is my son’s and he obviously does not care about it after leaving it in my backyard for 2+ years. I have a rebuilt IP from Marty that will be my next test.
 

Will L.

Well-Known Member
Messages
14,394
Reaction score
22,042
Location
Boulder City Nv
If you let the return line leak on the ground out the ip (or a bucket) and the ip allows fuel to flow through, then you connect it to the tank and fuel stops flowing through the ip- it is plugged.

If fuel does not flows out the return line onto the ground when disconnected - it is in the ip.
Remove fuel shut off solenoid and try again. If still no fuel flows out return that is open - problem is in the ip, or in the pmd controlling the ip. but to reach this conclusion you need to verify the screen and tiny holes on the ip inlet fitting is clear, and that you have proper fuel pressure going into that fitting.
 

Big T

Well-Known Member
Messages
6,276
Reaction score
8,813
Location
Fullerton, CA
If you let the return line leak on the ground out the ip (or a bucket) and the ip allows fuel to flow through, then you connect it to the tank and fuel stops flowing through the ip- it is plugged.

If fuel does not flows out the return line onto the ground when disconnected - it is in the ip.
Remove fuel shut off solenoid and try again. If still no fuel flows out return that is open - problem is in the ip, or in the pmd controlling the ip. but to reach this conclusion you need to verify the screen and tiny holes on the ip inlet fitting is clear, and that you have proper fuel pressure going into that fitting.
Already posted pics of the IP inlet screen and it is clean. Already posted video of fuel pressure to IP and it was 6+ PSI and that was the old LP. Now it has the Walbro. Either way it gushes before the IP and maybe a trickle out the clear return line when disconnected. Don’t know how I could be more clear on this.

I am in Montana, while truck is in SoCal. I will be down there October or November. Will do final tests with fuel pressure gauge, then remove solenoid. Last time I fully removed solenoid, some fuel came up and flowed over, but it was no gusher.

I will order another PMD to test. I can always use a back up for either the ‘94 or the ‘99.
 
Last edited:

jrsavoie

Recruit
Messages
6,417
Reaction score
1,889
Location
Rural Clifton, Illinois
Already posted pics of the IP inlet screen and it is clean. Already posted video of fuel pressure to IP and it was 6+ PSI and that was the old LP. Now it has the Walbro. Either way it gushes before the IP and maybe a trickle out the clear return line when disconnected. Don’t know how I could be more clear on this.

I am in Montana, while truck is in SoCal. I will be down there October or November. Will do final tests with fuel pressure gauge, then remove solenoid. Last time I fully removed solenoid, some fuel came up and flowed over, but it was no gusher.

I will order another PMD to test. I can always use a back up for either the ‘94 or the ‘99.
Has voltage to and from the pmd been tested?

I had a pin connection on the connector that normally goes to the pmd on the ip, go bad. The 94 truck, just shut down while my wife was driving down the road. A different extension harness made connection - after I had tried several other harnesses.
 

Big T

Well-Known Member
Messages
6,276
Reaction score
8,813
Location
Fullerton, CA
Has voltage to and from the pmd been tested?

I had a pin connection on the connector that normally goes to the pmd on the ip, go bad. The 94 truck, just shut down while my wife was driving down the road. A different extension harness made connection - after I had tried several other harnesses.
No. Please explain how to test.
 

jrsavoie

Recruit
Messages
6,417
Reaction score
1,889
Location
Rural Clifton, Illinois
I thought it was in the 6.5 diagnostics post.

It is in the thread about my 1994 from a few years ago. I will look for it.

 
Last edited:

WarWagon

Well it hits on 7 of 8...
Messages
10,030
Reaction score
6,446
Location
AZ
You have a shaft driven vane pump in the IP between the fuel inlet and the rest of the IP. Unless it's turning the only fuel you see is leakage through it. The engine must be turning the IP to flow fuel.

Spin the engine over and see how much fuel you get out.

IMO with the past 9 pages the point is reached where the shaft has sheared off in the IP or something else is refusing to flow fuel through it.

Compare the fuel return on a running 6.5 when cranking (unplug PMD) and this problem will become very clear. :wideyed:
 

colbythekid

Member
Messages
157
Reaction score
21
Location
Fullerton, CA
It was the same flow out the return line when cranking the engine.


This is the flow coming out a different IP not attached to the truck but just hooked up to the fuel system.

I'll try and change the IP to a rebuilt one today and see what happens.
 

Will L.

Well-Known Member
Messages
14,394
Reaction score
22,042
Location
Boulder City Nv
Is that first video where it is flowing good the one that attaches to the ip?
Also, inspect that hose really well- I have seen Many fail inside and create a flap that plugs the line right at the fitting. A bug part of why I want to see metal “Tee” used fat the ip for fuel pressure gauge.
 
Last edited:

WarWagon

Well it hits on 7 of 8...
Messages
10,030
Reaction score
6,446
Location
AZ
This is the flow coming out a different IP not attached to the truck but just hooked up to the fuel system.
Compare to a running 6.5 when cranking. This video is leakage past the vane pump plus draining the fuel out of the hose. It doesn't tell us what we need to know. The IP vane pump does not "flow on fail". When it turns fuel moves like a BP Gulf oil spill.

Swapping the IP likely will solve the problem anyway.

Hose flapper example at inlet to IP. Kinked shut hoses soft from Biodiesel also gave me no end of trouble.


hose_flapper.jpg

Hose_flapper1.jpg
 

colbythekid

Member
Messages
157
Reaction score
21
Location
Fullerton, CA
Is that first video where it is flowing good the one that attaches to the ip?
Also, inspect that hose really well- I have seen Many fail inside and create a flap that plugs the line right at the fitting. A bug part of why I want to see metal “Tee” used fat the ip for fuel pressure gauge.
The first video shows fuel coming from the fuel filter before the IP.

The second video is coming out the IP. The fuel flow coming from the IP is about the same when the engine is cranking or not.
 
Top