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Lift Pump Not Working, Where to Start

After I replaced the valve covers on my truck I couldn’t get it to run. It ran fine before. I had no fuel flowing through my IP when my wife tried cranking it with me watching the clear line on the IP. I got to looking everything over and realized that I didn’t plug the PMD extension harness back in. After I reconnected it it fired off shortly after. Make sure that the PMD and harness is good and is plugged in.
 
Jaryd said:
After I replaced the valve covers on my truck I couldn’t get it to run. It ran fine before. I had no fuel flowing through my IP when my wife tried cranking it with me watching the clear line on the IP. I got to looking everything over and realized that I didn’t plug the PMD extension harness back in. After I reconnected it it fired off shortly after. Make sure that the PMD and harness is good and is plugged in.
Click to expand...

I am buying another PMD and harness before I go the replacement IP route. I can use a spare for my ‘99 Suburban and it’s a cheaper step than replacement IP.
 
@Big T IMO you need to pull the return off one of your running 6.5's and put it in a bucket. Look at the amount of fuel it dumps in a 10 second cranking. It's a lot of fuel and I politely suggest it may not be clear to you. Think BP well blowout oil spill. :woot:

With all you have tried I am not clear how much fuel you got out of the stop solenoid hole and how much fuel is going through the IP?

I also suggest a Known Good PMD off another rig because it's cheaper and New Parts are not always good parts.
 
Look at every pin in the PMD harnesses. Be sure that they are all hanging out where they belong.
Check with an ohms meter to be sure continuity is flowing through all of the connectors and wires.
 
You guys are ok on testing pins, pmd, pmd cable, etc IF it was getting fuel through the ip and not out the injector lines.
But that stuff is WRONG for this problem. Chasing a shadow down the rabbit hole.

If the fuel does not flow out the return of the ip at the same basic rate as it comes from the liftpump- the pmd makes no difference.
It’s like testing pmd when the fuel tank is empty. Focus on known primary problem.

dont buy another pmd right now. Why? Because you are 70% of the way to buying a new ip, which always come with a new pmd.

IF YOU DONT HAVE FUEL GOING THROUGH THE IP, A PMD CAN NOT FIX THE PROBLEM.
 
WarWagon said:
@Big T IMO you need to pull the return off one of your running 6.5's and put it in a bucket. Look at the amount of fuel it dumps in a 10 second cranking. It's a lot of fuel and I politely suggest it may not be clear to you. Think BP well blowout oil spill. :woot:

With all you have tried I am not clear how much fuel you got out of the stop solenoid hole and how much fuel is going through the IP?

I also suggest a Known Good PMD off another rig because it's cheaper and New Parts are not always good parts.
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It was not a gusher out of the stop solenoid hole. It rose and spilled over.

I checked the screen on the incoming to the IP and it was completely clean.

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Tomorrow I fly from Orange County to Missoula. Will be there through the first week of July, then back down to Fullerton. Wife is getting a shoulder replacement done to become the bionic woman. Will be down there for at least 2 weeks and will deal with the Suburban again. Sounding like a new IP.
 
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How is the fuel coming out of the inlet pipe to the IP that you disconnected from the IP to check the screens? Although subjective, if it's not a gusher with the lift pump running I would ask how old is fuel filter, remove the last ditch screen in the FFM, and suspect a hose kink or flapper between the FFM and IP.

You have good pressure at the FFM water drain: it then goes through the filter and last ditch screen.

Really need to feed the IP out of a bucket as it's the second one with problems.
 
Yes to using bucket (or small gas can preferred incase you knock it over) with hose to ip, the return from ip to bucket. That bucket needs to be elevated above engine, like on top of 6’ ladder next to truck so it gravity feeds ip. Or if you have a spare lift pump laying around, bucket on ground.
DONT reuse any of the old fuel hose.
 
WarWagon said:
How is the fuel coming out of the inlet pipe to the IP that you disconnected from the IP to check the screens? Although subjective, if it's not a gusher with the lift pump running I would ask how old is fuel filter, remove the last ditch screen in the FFM, and suspect a hose kink or flapper between the FFM and IP.

You have good pressure at the FFM water drain: it then goes through the filter and last ditch screen.

Really need to feed the IP out of a bucket as it's the second one with problems.
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That pressure measurement was at the IP end of the line from the FFM.
 
But not with proper amount of fuel flowing through the ip by the sounds of it. That raises the pressure you read. 8-14 psi needed WHEN fuel flowing through ip instead of getting backed up.

Right now, take huge breathe and whistle high pitched and softly without changing pitch or volume. In the middle of it, use finger to plug lips. Your cheeks swell. Pressure goes up because volume of flow changed even though supply maintained. Boyles law.

If fuel is not flowing through ip properly- the psi on gauge becomes a worthless number.

you had 6 psi dead headed (no actual flow) i can only guess but that is probably 0.5 when flowing properly at idle. Way into negative (vacuum) at high rpm. Translation- pitting the heck out of the pump housing where the rotors rub to create pressure and early death of ip results.
 
Will L. said:
But not with proper amount of fuel flowing through the ip by the sounds of it. That raises the pressure you read. 8-14 psi needed WHEN fuel flowing through ip instead of getting backed up.

Right now, take huge breathe and whistle high pitched and softly without changing pitch or volume. In the middle of it, use finger to plug lips. Your cheeks swell. Pressure goes up because volume of flow changed even though supply maintained. Boyles law.

If fuel is not flowing through ip properly- the psi on gauge becomes a worthless number.

you had 6 psi dead headed (no actual flow) i can only guess but that is probably 0.5 when flowing properly at idle. Way into negative (vacuum) at high rpm. Translation- pitting the heck out of the pump housing where the rotors rub to create pressure and early death of ip results.
Click to expand...

It’s a new OEM style lift pump.

I do have a brand new Walbro pump for it.
 
There is no factory style inline lift pump that properly feeds a ds4. The one that used to exist quit getting made in 2001 or 2002.

But you need to solve the other issues first imo. Basically measure the volume of fuel going into ip, almost the same volume should come out the ip return when cranking the engine.
 
I do have a new reman ip setting here I could send over.
Problem with it is, it is a SSDS rema’d pump so the reliability of it may be a crap shoot. Next thing is it has been setting for about four years so, it may be plugged with old fuel and whatever else happens to reman pumps when they set for too long.
If there are any opinions of sending this over for a test run then please let us know. I sure would not want to put You through the trouble of trying this pump then have it found to be a bad reman job or a plugged up pump.
 
Alright, while we’re down in Fullerton, thought I would revisit this IP issue. As instructed, I connected the IP to a 5 gallon jug of fuel on top of a ladder. Siphoned the fuel down the clear hose to the IP. Pulled the clear return line.

Test #1 is with a remote Dtech PMD.

youtube.com

Test #1 Dtech PMD

youtube.com youtube.com

Test #2 is with a remote Stanadyne PMD.


The second attempt pulled some fuel through the IP, but not much.
 
Big T said:
So I did the suggested tests. Posted the videos and results and no responses? Do I need to start a new thread?
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Should not need to start a new thread.
Everyone must be busy today. I sure have been. A real 💩 show over here.
I’m just not familiar enough with what needs to be going on with the pumps to give You a good answer.
Maybe pull a GP and see if there is a mist of fuel emanating from that cylinder.
 
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