1994 gmc 3500hd, 6.5 turbo diesel.

[Boblaw66]

MECHANIC needed, 20 mins west of Philadelphia for my 1994 gmc 3500hd, 6.5 turbo diesel, dump. Thanx
Or for sale, new, ip, ops, fuel pump, grounds, new relocated pdm, ran great for mos after all that stuff but after a while it dies, then starts after 10-15 minutes. 484-213-6093

 

[Will L.]

@Boblaw66 if you like, we might be able to walk you through the repairs.
This sounds like one of two issues.
Air intrusion into the fuel system or a lift pump failing.

Stop at any hardware store and get 1/4” diameter clear tubing, replace the 6” long piece coming out the front of the ds4 in an u shape. Then watch that for bubbles going through which indicates air is getting sucked into the fuel line. Basically a fuel leak before a pump wont leak out fuel but will instead suck in air. The ds4 can’t handle it and ya repair the leak.
To find the leak, put 1-2psi air pressure in the fuel tank with engine off. This will cause fuel (or air) to leak out and you can hear it or see it. Usually where the rubber lines are connecting to metal lines, or rusted metal lines.

For lift pump- Add a T at the inlet fuel line of the ds4 and monitor pressure when starting/running. 8-14psi is desired. But anything above 1psi should allow it to start. When the lift pump is bad, the ds4 will suck fuel past the lift pump and run but does so poorly with harder starts, loss in power, loss in mpg all possible.

Ideally use a metal T fitting and mount a fuel pressure sensor there, mounting a gauge permanently in the dash to monitor while driving. This is instant diagnostic when something is going on. A bad lift pump will ruin a good ds4 in no time flat. So the gauge becomes insurance to not ruin a ds4.

Most of the time people learn the factory lift pump is inadequate and has dhort lifespan. You sound like you are about to eliminate the 6.5 or the truck all together? If keeping the truck no matter what- strongly consider if the lift pump is bad- investing in a fass lift pump with filters. Pricey but the best water stopping ability, way better filtering, and the pump last basically forever. No matter if 6.5, Cummins, duramax, etc- they all do better with them than factory filters and Lift pump. You eliminate the factory filters when this is added btw.

 

[Will L.]

There is a Hummer mechanic- same engine- he MIGHT work on it for you.
Tor is his name, has a good reputation for quality but some Hummer mechanics only do Hummer, just like some pickup mechanics wont work on Hummers or RVs.
He is in South Jersey

Tor Fossnes and H1 One Stop Shop

 

[jrsavoie]

I wouldn't rule out the PMD or resistor even though they're new.

Where did you get your parts?

There's also thevfuel fill cap and the optical sensor noise harness to investigate and rule out.

 

[MrMarty51]

Throw a new PMD at it and see what it does.
As @jrsavoie suggested, be sure it has a new resistor installed within the PMD plug too.
I was typing same time he was posting.

 

[MrMarty51]

That sounds to me like the typical PMD failure.
On My truck I have three PMDs mounted on heat sinks with remote harnesses strung to each one.
One driver is a Dorman that I am currently running on and Oriellys life time warranties those, dont know if other parts stores does or dont.
The other morning started my truck, made it the length of one block side. Boom, engine stalled. Turned off switch, back on and it started, made the trip around the rest of the block to my garage, opened the hood, swapped harnesses and went on about my business. Got back home and pulled the faulty unit, called Oriellys, the counter man said we have never sold one of those. Had to furnish my receipt, took in the receipt and the bad driver and he ordered in a new one.
He had not looked far enough back in the years.
The suppliers in the forum handles the Flight Systems pump drivers so if it can wait maybe order one in from them. Leroy Diesel or QuadStar tuning.
I am to the belief that Dorman purchased the Flight Systems plant but they still are making them in the USA and thats a big bonus in my books.
FS drivers too are warranted for life.
Best to order two in case of a failure then You can keep going while the replacement is in the mail.

 

[MrMarty51]

Oh yeah, also, I have the top side harness connectors and the bumper ends all three numbered, if one fails then I know which one it is and can then remove it without guessing.
Also, I have not had to replace a pump driver for l quite some time.
I no longer call them a PMD or pump mounted driver. They no longer are attached to the injection pump so I call them pump driver or just driver.

 

[Turbine Doc]

Fuel Solenoid Driver/FSD (actual function) is what I call them after removing from IP, mine mounts on heat sink inside my Buck Stop Bumper, I keep a spare in the truck pre mounted to a plate on case I need to swap out, I can just swap to the spare one and put in bumper, permanent mount later if needed, so far no fails of the original Heath one installed back around 2007

 

[Boblaw66]

Throw a new PMD at it and see what it does.
As @jrsavoie suggested, be sure it has a new resistor installed within the PMD plug too.
I was typing same time he was posting.

Thanks, I did put 2 new pdms in, I had spares and the new relocation harness.

 

[Boblaw66]

That sounds to me like the typical PMD failure.
On My truck I have three PMDs mounted on heat sinks with remote harnesses strung to each one.
One driver is a Dorman that I am currently running on and Oriellys life time warranties those, dont know if other parts stores does or dont.
The other morning started my truck, made it the length of one block side. Boom, engine stalled. Turned off switch, back on and it started, made the trip around the rest of the block to my garage, opened the hood, swapped harnesses and went on about my business. Got back home and pulled the faulty unit, called Oriellys, the counter man said we have never sold one of those. Had to furnish my receipt, took in the receipt and the bad driver and he ordered in a new one.
He had not looked far enough back in the years.
The suppliers in the forum handles the Flight Systems pump drivers so if it can wait maybe order one in from them. Leroy Diesel or QuadStar tuning.
I am to the belief that Dorman purchased the Flight Systems plant but they still are making them in the USA and thats a big bonus in my books.
FS drivers too are warranted for life.
Best to order two in case of a failure then You can keep going while the replacement is in the mail.

I ha e pdm on ip, one on the front grill and one I just put In temporarily with zips to the master cylinder.

@Boblaw66 if you like, we might be able to walk you through the repairs.
This sounds like one of two issues.
Air intrusion into the fuel system or a lift pump failing.

Stop at any hardware store and get 1/4” diameter clear tubing, replace the 6” long piece coming out the front of the ds4 in an u shape. Then watch that for bubbles going through which indicates air is getting sucked into the fuel line. Basically a fuel leak before a pump wont leak out fuel but will instead suck in air. The ds4 can’t handle it and ya repair the leak.
To find the leak, put 1-2psi air pressure in the fuel tank with engine off. This will cause fuel (or air) to leak out and you can hear it or see it. Usually where the rubber lines are connecting to metal lines, or rusted metal lines.

For lift pump- Add a T at the inlet fuel line of the ds4 and monitor pressure when starting/running. 8-14psi is desired. But anything above 1psi should allow it to start. When the lift pump is bad, the ds4 will suck fuel past the lift pump and run but does so poorly with harder starts, loss in power, loss in mpg all possible.

Ideally use a metal T fitting and mount a fuel pressure sensor there, mounting a gauge permanently in the dash to monitor while driving. This is instant diagnostic when something is going on. A bad lift pump will ruin a good ds4 in no time flat. So the gauge becomes insurance to not ruin a ds4.

Most of the time people learn the factory lift pump is inadequate and has dhort lifespan. You sound like you are about to eliminate the 6.5 or the truck all together? If keeping the truck no matter what- strongly consider if the lift pump is bad- investing in a fass lift pump with filters. Pricey but the best water stopping ability, way better filtering, and the pump last basically forever. No matter if 6.5, Cummins, duramax, etc- they all do better with them than factory filters and Lift pump. You eliminate the factory filters when this is added btw.

I did put a new ac delco lift pump but same thing. I have a Detroit motor. How do I put air in the tank, just with my air Compressor? Do I ha e to make a seal around the fuel cap? Thanx in advance. Also, for the clear hose, I install it the way I take off the other hose or do I leave 1 end off and do the air?

 

[Will L.]

The clear line replace the rubber one completely. You will leave it permanently. If you use the clear pvc from hardware stores it will last 3-5 years. Some people add new screw style hose clamps, some dont, I do.

The new lift pumps- the AC Delco EP158 is the best of them. But I have seen them die in less than a year. Also every great once in a while it will be a new defective- that can be for any new part unfortunately. Even so, a restriction in the line somewhere after the lift pump won’t show up unless you have a fuel pressure gauge that has the T fitting at the inlet for the injection pump.

To put air in the tank- safest move I saw was using a pressure regulator on the hose from a compressor. Then the hose end just wrapped with a shop rag to seal it up somewhat. Professional mechanic will use an old gas cap and drill it for an air fitting- but for a one time use- doesn’t make sense. Another option I saw once was a guy seriously used a bicycle pump so he could add it slow- but had the modified gas cap so it stayed sealed fairly well.
There is a vent that will dump the air but making the tank swell up is a
HUGE NO-NO!!! You can ruin the fuel tank that way- basically pop like a balloon.
So be cautious with it. Take your time figuring it out. Remember diy you are saving $175 per hour on average shop rate. So pay yourself accordingly in time to learn.