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Mark, ASE Certified Technician
Category: GM
Satisfied Customers: 847
Experience:  34+ yrs Dealership Exp. - Fully State & ASE Certified - GM Master & GM World Class Tech
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GMC: turbo diesel..shuts..going down..No check engine light.

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I have a 94 6.5 GMC turbo diesel. It shuts off going down the road. No check engine light. It doesn't do it all the time. It might do it 2 or 3 times a week or it might no do it for a month. Sometimes it will start right back up other times it takes an hour. How do you check the PDM?
Greetings, my name is Mark.

I will do my best to help you. Please do not accept my answer unless you can leave positive feedback. It is important to me that I have helped you and you are satisfied with my answer. I don't know if you are a tech or just a person who is attempting to repair their own vehicle. I only know as much about your issue as you have told me on your post. My answers will be base on the amount of information I am reading. Try to give me as much detail as you can, so we can accurately solve your problem.

Even though you do not have a "check-engine" light on, you most likely have codes stored. Not all codes will trigger a light, OR, it may only put it in history. Does sound to me you have injection pump issues. However, you could have a "crank-sensor" failing.

At this point, it does no good to just guess, or to "part-dart" it. You have asked about the PDM. There are some out there that recommend installing a new one out and away from the pump. Not so sure I agree that it makes a difference. I will say I haven't had too much success replacing parts on the pump. It is totally an electronic pump, computer controlled. You really should have a scanner and get some readings.

I can help you with any diagnostics or repair procedures if we know what's going on. Below, is a picture and description of your fuel system and pump.

If I were a guessing man, and note I said "guessing", you might have a "shut-off" solenoid going bad. That would be number 4 in the picture. This is what shuts the pump off when you turn the key off. I have replaced them before with some success in random stalling.

Fuel System Description

The fuel injection system has a PCM controlled fuel injection pump mounted on top of the engine under the intake manifold. The pump is driven by the camshaft through two gears, one attached to the front of the camshaft and the other attached to the end of the pump shaft. These gears are the same size and have the same number of teeth; therefore, the injection pump shaft turns at the same speed as the camshaft.

Electronic Fuel Injection Pump

Object Number: 54847  Size: LF

(1)Fuel Solenoid Driver
(2)Optical/Fuel Temperature Sensor
(3)Fuel Inlet
(4)Engine Shutoff Solenoid
(5)Two Stage Housing Pressure Regulator
(6)Injector Timing Stepper Motor
(7)Fuel Solenoid

The injection pump is a high pressure rotary type that is controlled by the PCM. The injection pump meters, pressurizes, and distributes fuel to the eight injector nozzles by way of eight high pressure lines. An outlet port in the injection pump allows the fuel to enter the fuel return system and then travel back to the fuel tank.

Mark and other GM Specialists are ready to help you
Customer: replied 6 years ago.
Sounds like that could be the problem. I am a Diesel mechanic ( MAC). I'll give it a try. Any idea what the parts might cost?
Hey..........nice to hear you turn the wrench a bit yourself.

Can't say I know the cost. It's been a bit since I have done this. We had a parts truck that had the diesel. I maintained it for years (amongst joe customer). The truck was hauled in on a couple of occasions for the inter. stall. I changed the "shut-off" solenoid on a guess and never saw it again for that problem. Got lucky.

I am guessing around 50-75 bucks. Don't quote me on that though. That part should still be available through GM or your diesel pump shop.

Take care, be safe, and keep me informed if you want.
Customer: replied 6 years ago.
Great! Thanks! I'll let you know how I make out!
Customer: replied 6 years ago.
Ok, finally got the part from the dealer and got it in. The truck is still stalling, any more suggestions?