Lift Pump Not Working, Where to Start

[Big T]

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.

I get SES and WTS lights.

PMD was known working before the IP change.

The lift pump wire looked like it was broken from a rub. It was just one of two. Wouldn’t mice chew them all?

 

[Will L.]

On the fss, i just unscrew it a ways. Put a small rag near it- Fuel will spill- so what. If the fuel starts spraying out the open injection lines- that tells you it was the problem.

Fuel flows through the clear line without a pmd in place.

Any damaged wires definitely need correction.

 

[Big T]

On the fss, i just unscrew it a ways. Put a small rag near it- Fuel will spill- so what. If the fuel starts spraying out the open injection lines- that tells you it was the problem.

Fuel flows through the clear line without a pmd in place.

Any damaged wires definitely need correction.

I will install the clear line and all injector lines but the front one on driver’s side.

So you want physical proof that the fuel solenoid is working? How about just pulling it out and observing the plunger working while someone activates the ignition?

The IP has the original PMD mounted on the side and was not used as we had a remote mounted PMD. What does connecting the remote PMD directly to the engine harness get me?

 

[Will L.]

I never bothered trying to see or feel the solenoid move by key- i just back it out and try starting. If it starts, turn key off, getvout and screw it in. Then I grab a meter and check power & ground to be sure it isn’t electrical fault keeping a good solenoid from working -1 in like 250 times a fuse was bad connection. Every other time it was bad solenoid.

But I always knew I had fuel flow without contamination including air first. GM says do that first wisely.

Bypassing the pmd Extension cable eliminates it as possible fail point, so long as you are 100% the other pmd is good.

Right now it is sounding 97% you have electric/electronic problem.

 

[smokymtn65]

Where did the extension cable come from? i beat my head against the wall over a bad "new" one.

 

[Big T]

Where did the extension cable come from? i beat my head against the wall over a bad "new" one.

Extension cable is from Leroy Diesel. It’s a 6 pin and was working before this IP swap. I will first do a detail check of its condition.

The square plug that goes into the top center of the IP has lost its locking tab, but it stays in there snugly.

IP nuts are 6 point, so I ordered 12 point versions from Unique Diesel (Peninsular).

I apologize for the delay on this work. I checked posts and this truck has been down since at least January 2019. This was due to a combination of multiple foot surgeries and then COVID interruptus which had me working from home at the Montana ranch (I know, tough life). Truck was having major stalling issues and we could barely get it to light before I just decided to go with a different IP. Son was thinking clogged sock in fuel tank, then lift pump, etc. Went through that process of elimination. I then verified here that the IP from the ‘95 engine we have would work and that is the direction I went. I did swap feed the beast fuel fitting and fuel solenoid from the old pump onto this one. The original fuel solenoid on this IP had a loose/wobbling body.

 

[Big T]

OK, duck out after a video meeting and did some more testing. Pulled the fuel shut off solenoid and the IP fills and spills over, but no fuel out the injection lines and the return line to IP is dry. I plugged the engine harness into the old PMD mounted on the IP and no difference. I inspected wiring at all the plugs and there is no damage that I can see from mice.

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[Will L.]

Darn. Was hoping it was an easy one for ya.
Either electrical or electronic.

 

[Big T]

Darn. Was hoping it was an easy one for ya.
Either electrical or electronic.

PMD? I can see if my son has another one.

What exactly does the PMD do?

Electronic? I have the manifold off, but all plugs are plugged in. Could there be grounds disconnected with the manifold off?

 

[ak diesel driver]

Check the 3 at the back passenger side of the intake manifold

 

[Big T]

I’ll try this one....

 

[Will L.]

Yup. You are at classic square 1 with 6.5 no start process.
Remove and clean all grounds. Swap with known good pmd- bypassing all extension cables if possible- and since on a heat sink- you can do that.

But you need the clear line and pressure read AT THE IP INLET. ——So crucial to watch PERFECT fuel flowing through it while cranking. I can’t tell you how many times people replaced ip, pmd, harnesses, and more to get mad and sell the truck. Then we put on a clear line and pressure gauge and made money flipping the truck sale.

 

[WarWagon]

What exactly does the PMD do?

It Pisses GM diesel customers off when it strands a brand new vehicle on the way home from the dealer. Or any other place it dies. Some get so fed up with the awful design they went with a DB2. Some even wrote a manual on how to convert to a DB2.

The PMD, Pump Mounted Driver, controls the fuel fill solenoid in the injection pump. It's the DS4's inefficient high power electronic replacement for the metering valve in a DB2. So a no fuel situation can be a PMD problem.

I would attempt running the SOB out of a 5 gal can at this point. If either fuel line is restricted it will not run. A restricted return line is a problem. The suggested clear fuel line is about the last step before you go hardcore on electronics.

After we verify it's got fuel with a clear line: do you have any scanning software? I wonder if it's not seeing any CPS or optical disc readings. Maybe disconnect one and then try a 30 second crank. Then reconnect and disconnect the other.

 

[Big T]

It Pisses GM diesel customers off when it strands a brand new vehicle on the way home from the dealer. Or any other place it dies. Some get so fed up with the awful design they went with a DB2. Some even wrote a manual on how to convert to a DB2.

The PMD, Pump Mounted Driver, controls the fuel fill solenoid in the injection pump. It's the DS4's inefficient high power electronic replacement for the metering valve in a DB2. So a no fuel situation can be a PMD problem.

I would attempt running the SOB out of a 5 gal can at this point. If either fuel line is restricted it will not run. A restricted return line is a problem. The suggested clear fuel line is about the last step before you go hardcore on electronics.

After we verify it's got fuel with a clear line: do you have any scanning software? I wonder if it's not seeing any CPS or optical disc readings. Maybe disconnect one and then try a 30 second crank. Then reconnect and disconnect the other.

I have the ChiCom GM Tech II scanner.

I tried the second PMD and no go.

Is the large square plug on top of pump for the optic sensor?

 

[Will L.]

yes that is optic sensor

 

[WarWagon]

Does the scanner show you cranking RPM? If so we could see if the ECM is seeing engine RPM. I don't know if it will show you CPS and IP RPM sensors? I never used that scanner.

One more thought on return fuel ... if for some reason the pump locked up and snapped the input shaft or isn't turning for whatever reason there will be no fuel flow on the return.

 

[Big T]

Does the scanner show you cranking RPM? If so we could see if the ECM is seeing engine RPM. I don't know if it will show you CPS and IP RPM sensors? I never used that scanner.

One more thought on return fuel ... if for some reason the pump locked up and snapped the input shaft or isn't turning for whatever reason there will be no fuel flow on the return.

Now this could be onto something. This IP was harvested off a good engine in a '95 Suburban that went through a rollover accident after hitting black ice. Have not hooked up the scanner....yet. I need to do some more checking with an assistant cranking the engine over.

 

[Big T]

Yup. You are at classic square 1 with 6.5 no start process.
Remove and clean all grounds. Swap with known good pmd- bypassing all extension cables if possible- and since on a heat sink- you can do that.

But you need the clear line and pressure read AT THE IP INLET. ——So crucial to watch PERFECT fuel flowing through it while cranking. I can’t tell you how many times people replaced ip, pmd, harnesses, and more to get mad and sell the truck. Then we put on a clear line and pressure gauge and made money flipping the truck sale.

Clear line between the FFM and IP? Install fuel pressure gauge between FFM and IP?

I’ve verified that it has fuel. Fuel squirt out of the bleeder valve. Fuel pours out of the line going into the IP. Fuel pour out of hole for the Fuel Shut Off Solenoid. The return line to the IP is dry and will remain dry because the IP is pumping nothing and the driver’s side injection lines are not connected. Even if they were, the IP is not pumping fuel.

I will try it with optic sensor disconnected. Then I will try it with CPS disconnected. After that I will put the original IP on because we at least got fuel out of that and the engine would light periodically. Hopefully, it was bad lift pump wire in the first place. If no success there, then I will send the original IP in for rebuild.

 

[ak diesel driver]

Did you ever check those grounds?

 

[Will L.]

Clear line is 1/4” return line coming out ip. The only time you put clear line between the FFM and IP is when you have air bubbles out the IP, but cannot find where the leak is. If no bubbles go into the IP, but bubbles come out, then the IP is leaking and sucking air or is causing cavitation inside the IP must be repaired.

Pressure gauge is after rubber line from ffm before metal inlet line of ip. The most common place of rubber fuel line failure is that piece just before the ip. Over the years I have had 3 people from this site send me pics of how that line failed and they replaced an ip mistakenly because of it. I have had 1 guy and 1 gal on hummer forum do the same. I did it 2 times in the fleet. 2 other guys 1 fleet and 1 dealership did it. CRAZY COMMON error. I know I sound dumb hammering this point but figure out why I have been saying it since I joined this forum. $100 gauge set up that stops early ip death and often stops replacing a good ip.

if you were getting tons of fuel coming out where the solenoid was removed when testing then the fuel pressure gauge waits for now.
But you still work should take the time andthe three dollars to put on the clear return.

Double check all the pins are not bent inside the connectors. Then get the scanner on there. The removed ip from crash should be fine. Never seen a crash damage an ip unless it got smacked which would have visible damage. This indicates the original ip wasn’t the cause to me.

yes optic/crank sensor test is good idea. Something electrical or electronic goin on here.
Does ecm work on both? Did you remove and clean the grounds? Have to scrub em- looking ok on outside doesn’t mean anything.