staling after 2 hours of use

[fixitguy1ca]

Hi
I have a 98 3500hd with the 6.5 turbo diesel. It starts and runs fine for the first hour or so then stalls as it is out of fuel. It usualy starts right up again and then stalls within 3 minutes, only to repeat the process. Throttle posistion or speed doesn't seem to make a difference. There seems to be no change in the exhaust as it stalls. I have changed the: booster pump under the cab, the transfer pump between the two tanks, the float module in the front tank, and checked the lines from the fuel tanks for leaks. I have also changed the fuel filter in the engine. I have ran the truck with the bleeder open to the point of empting the tanks and got no air bubbles. It has the electronic injector pump, and throtte control. I have been a diesel tech for 15 years but this one has me stumped. Oh and yes i am in montreal so i don't think it is the module on the intake manifold that is overheating as it is cold to touch yet the truck still stalls. any help or ideas would be appreciated. Thanks.

[Mark Rinker]

Welcome aboard.

From your description, and thorough troubleshooting of the fuel delivery system, I'd say it is likely the PMD. (Also referred to as the FSD...)

The PMD/FSD doesn't need to overheat to fail. My advice would be to buy one mounted to a heatsink with a harness extension - leaving the 'iffy' one on the injection pump as an emergency backup in case it happens again.

Lots of used PMD/FSDs out there floating around if you need to save money, but the cost is obviously reliability over the long run...

Good luck!

[fixitguy1ca]

is there any way to test the PMD?...I have already sunk about $1000 into this only to not fix it. I am reluctant to throw more money into a guess. thanks for your input.

[bp250065]

I hear you, I have the same problem, but Unfortunatly there is now way to test the PMD unless you have another one that you know is good to try.

[Robyn]

PMD failure is the one item that has plagued these engines since the 1994 model year.

The PMD (Little black box on LH side of IP) is best left right where it is and abandoned there.

You can use a small screw driver to unclip the harness that plugs into the rear side of it and then fish the wire harness up and out.

Usually there is enough slack that you can get ahold of it easily.

The DTECH brand of aftermarket replacement PMD has proven itself to be reliable.

As was mentioned, a remote mount (cool area away from engine) and an extension harness (many places online to buy one as well as TDP supporting vendors) is the best plan.

Use a number 5 resistor with the new PMD (no way to tell what the old one is) The number 5 resistor will work with most pumps and the ECM will likley not complain. (The resistor plugs into the opening in the PMD and fits over the pins and is self explanatory when you see it)


A PMD thats mounted on the pump can have a very short life span.
I have seen new Pumps installed by the dealers back in the day, that worked for less than 30K miles before they failed.
The Pumps are not usually the issue but instead the PMD.

If your rig has displayed any codes (SES LIGHT ON ) check these or get them checked first.

It is very common for a PMD to fail and not set any codes. They can trip once in a while if the rig is rolling at speed when the PMD fails.

You might get a P1216 or a P1217 depending, but normally no codes set when the PMD fails

Keep us posted

Robyn

[JohnC]

2 hours? How is the tank vent?

If you have a scanner, and can monitor solenoid closure time while it is stalling, sometimes you can see it act up right before the stall.

[fixitguy1ca]

After 5 days of use now I can say that it was the pmd. I also installed the cooler on top of the intake. I have removed the old pmd from the pump and I think i have found a way to repair it. The two transistors on the back of the unit had come loose. I have disolved a the epoxy just to see how it failed. I am a component level electronics tech as well. One of the transistor leads had broken the solder joint to the pcb. This left the unit running on 1 transistor which was heating up into thermal shutdown. I repaired the broken solder, and tightened the transistors to the heat sink(case) I have been running the repaired unit for 2 days now in another tow truck and it has yet to fail. took about 2 hours of soaking to clean the epoxy and about 15 minutes to repair the unit. Good way to save $300 in the future. I had a way to test the existing transistors, but I reccomend, that anyone wishing to repair thier own unit buy a new pair of transistors (less than $5.00) from any electronics component supplier.

[Splitrimz]

Do you think it is possible to measure the transistor leads to any of the pins on the case connector to determine continuity? I would love to experiment with a couple of failed units that I have laying around.

What did you use to dissolve the epoxy.

I have a couple of old PCms lying around that I would love fiddle with.

Thanks

[fixitguy1ca]

use Klinks epoxy thinner to disolve the epoxy. It is available at hardware stores and used to refinish bath tubs and sinks. I do not think it would be possible to test for continuety on the pins outside the case, but I am not sure. The repaired unit is running in another truck so I cannot see the schematic or pin out. If they are just lying around tho it is worth trying to repair them as they are worth $$ if fixed.

[Warren96]

Klinks epoxy thinner, and what kind of transistors did you use 2N3773?