• 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

Big T

Big T

Well-Known Member
Messages
11,918
Reaction score
26,353
Location
Fullerton, CA
Got the batteries in on the '94 and the lift pump is not working. So where do I start? Son says he installed new lift pump. Can't hear it working. Son says he also installed new OPS. Were is this located? Where do I test on harness to make sure it's getting power?

I also have LeRoy's original replacement lift pump and his replacement harness, plus a pre-filter set-up, all NIB.b Have one weekend left in SoCal, but can extend.
 
Did the engine run? If yes, you can open the t-valve and see if fuel is flowing.
If not, you can jump the relay and then open the t-valve to see if fuel is flowing.

The OPS in a 94 should be on the back near the firewall to the driver side of the FFM.
 
JMJNet said:
Did the engine run? If yes, you can open the t-valve and see if fuel is flowing.
If not, you can jump the relay and then open the t-valve to see if fuel is flowing.

The OPS in a 94 should be on the back near the firewall to the driver side of the FFM.
Click to expand...

It ran, but poorly, thus swapping in known working IP.

I opened t-valve, nothing. I opened FFM and no fuel coming in.

Where is the fuse?
 
The new Leroy Diesel harness I believe has a fuse in one of the wires, not a fusable link. If not then be sure that the power source that it is hooked to is getting voltage.
 
Big T said:
Son says he also installed new OPS. Were is this located?
Click to expand...

OPS back of engine driver side top. Buried by the Glow Plug controller relay.

I would jumper 12V direct to lift pump and "quality check" new parts. Make sure you get the "+ -" proper.

Check there is 12V at the OPS harness on any of the 3 pins. It's +12V, gauge reading, lift pump.

Did 1994 have a separate single fuse by the power block like the 1993's? Or does it have a underhood fuse center like 1995?
 
Installed the Leroy harness and when I went to plug it into the lift pump, red lead from the pump to the plug was broken:
842BD999-0B05-4158-848B-258BB1E7D39C.jpeg9A7C59DF-B37E-4170-984D-349FD9DE3BEB.jpeg

Now I’m getting fuel to the FFM (cover was leaking initially) and to the bleeder valve. I have not attached the injector lines on the driver’s side and not getting fuel there after much cranking.
 
OK getting 14v to the fuel solenoid. Can hear it click open and close when wife turned on the ignition key. Confirmed that fuel is pouring out the fuel line connected to the IP elbow (feed the beast fitting). Still no fuel coming out the injector lines.

The 6 pin connection below was originally on the PMD plug of the engine harness, but it will not fit into remote 6 pin PMD harness as they are both male side 6 pin. Not sure where it goes. Nothing is plugged into the PMD that’s still on the IP.
D0C3AA11-68F3-496A-BEFA-B44154321716.jpeg727CEB49-9D1D-403B-808B-AE61DDFC5566.jpeg
 
So let me back up to where this started. Son was having trouble with the truck now 2 years ago. He replaced the lift pump, but it was still barely running. Not sure when the wire lead from lift pump to the plug broke. Just too much time has passed. So I swapped in the IP from the engine harvested from the ‘95 wreck. Verified here by model number that it would work. Truck has a remote mounted (bumper) PMD and harness with 6 pin plug. Verified that fuel is getting to the IP. Verified that the fuel solenoid is getting power and is working. Can’t get fuel out of the 4 disconnected injector lines at the injectors on driver’s side. What should I do next to trouble shoot this? Disconnect an injector line or two at the IP and test for fuel there?

Would like to get this truck running, timed, etc., after which I will replace timing chain and gears.
 
Will L. said:
Almost Computer time boss.

Don’t bother with other side or lines at ip end. They will all be dry.

Bypass fuel shut off solenoid yet?
Fuel flowing through clear line when cranking?
Click to expand...

No on bypass fuel solenoid. How would I do that?

Clear line not installed, but I’m not getting fuel to the injectors which are upstream.
 
If fuel isn't flowing out of the IP it isn't going to run. This can include a kinked or restricted hose on the return side. The clear return line would verify fuel flow through the IP.

You have enough injector lines disconnected to purge air IF it was getting fuel or any fuel commanded. No need to remove more.

The fuel "shut off" solenoid is unthreaded from the IP and you use a thread similar to faucet aerators for a nice plug. As you noted it thump I wouldn't bother. This is a redundant test to the clear fuel line on the return. If it's stuck shut you get NO return fuel flow, period.

Do you get the SES and STS lights on a bulb check indicating the ECM is alive?

I would remove the PMD extension harness and temp move the (or a known good working PMD on a heatsink) to the OEM harness.

The wire to the lift pump looks cut. That has F'N mice type critters written all over it. A wire harness inspection may be in order.
 
You must log in or register to reply here.
Back
Top