Hi - new to the Forum - bought a used 94 Chevy 3500 6.5 Diesel Dually a couple weeks ago with 211+K miles on it. Was told it has a rebuilt engine - but who knows if thats true or not. Got a pretty good deal - so wasn't too worried about whether it does or doesn't.
We were told upfront that it needed a new PMD, that the truck would stall. Also the truck runs rough - engine vibrates at lot in idle.

Here's the history - test drove for about 5 miles (no stalling); turned engine off for about 30 mins then after driving about 3 miles it stalled; threw it in neutral-turned off and back on, back into drive and it ran fine for another 5-6 miles. Then stopped & turned off the engine for fuel; drove another 3-4 miles; stopped and turned off engine for 30 mins; drove another 5-6 miles; stopped and turned off engine for 15 mins; then drove 100 miles - no issues.

Couple hours later drove 12 miles no issues, stopped and turned off engine, on return trip of 12 miles truck stalled again - restarted in neutral - came on home.

Next day made a couple stops doing errands, after 2nd stop and driving 3-4 miles uninterruppted it stalled - again restart in neutral. AFter that stall we made about 4-5 more stops (no problems with stalling - engine would start right up after each stop), then we drove about 60 miles non-stop with no issues.

Each time we've driven it, it's been a repeat performance - one stall usually within about 5-10 miles out or we might make it 10-12 miles - turn it off while we shop or have dinner and then on the return trip it will stall. Each time restarting while rolling along.

So after reading a lot about the PMD problems - decided to try a used PMD with the extended wiring harness.
Did a lot of reading about the PMD and stalling issues and rough idling and decided to try the PMD route. Found a used PMD with the extension harness and installed it up on the motor mounts. Drove about 7 miles and it stalled again!!!! Restart on the fly, no problems getting to our destination. On the return no problems. Then we took it back out again and drove it for 40 miles or so with a couple stops with no stalling. Next day 25 miles no problems - coming back stalled again - restart and kept going.

So did I screw up buying a used PMD? (I can return it) OR does it sound like something else. I'm NOT a mechanic - and fortunately I have a really good diesel mech I can take this to, but I'd just like some idea of what I might have going on. This truck was purchased by my daughter (first vehicle) to haul her horses - and right now we realize the danger of trying to do so.

Thanks to whoever offers insight.

 

ok first did you pull the chip out of the old pdm or atleast check to see if the ohm number is the same? second i would never reccomend a used pdm. is the pdm on a cooler? is your uplift pump working? is the water/filter clean? are you leaking any fuel and its getting an air pocket? and finally any codes? check engine light

 

Thanks for the input - I purchased a new resistor (is that the same as the chip)? I know purchasing a used PMD was probably not a wise idea - but I did - The PMD is on a cooler. Don't know how to get the codes. No check engine light.

 

yes the resistor is the same as the chip its located inside the plug on the pdm.and usually the reason someone has a used pdm is because its actually bad and there trying to get a few bucks back to offset the cost of a new one..have you checked the lift pump located on the driverside frame rail under the drivers seat? how old is the diesel in the tank? have you drained or replaced the fuel/water separator filter?another thing if your lift pump is getting power and runs when you turn the key on is check the fuel line bleader valve located on the front top of the engine is to break it open and turn the key on but dont start it. if fuel is comming out then pull the line off the back passanger side fuel injector and turn the key on and try to start it and see if fuel comes out.. now keep in mind if the pdm is working the fuel will fly out so cover it with a rag to keep it from spraying everywhere and shut the truck off asap if it does start.. if you have no fuel then the used pdm is no good.. but before you replace it check all the connections and make sure there clean and have good contact

 

Any codes? Does sound like a pmd

 

Thanks to all - too late and dark to try your suggestions, but we will tomorrow evening. Appreciate the detail on where to find these parts etc. I had read about the checking whether fuel was coming, but didn't know where to look - you helped describe this so well.
I will post our results, when we have time to take a look.

 

best way to look for fuel is to twist the cap on top of the fuel filter and crank the truck over and see if fuel comes out

 

OK - we twisted the cap on the top of the fuel filter - 2-turns had been suggested and we turned the key to the ACC 'on' and off, but never actually cranking/starting the engine. No fuel came out - so I'm thinking the lift pump needs to be replaced - we're gonna change the fuel filter at the same time.
Any thoughts - did we test it correctly?
As you can tell I'm NOT a mechanic - just trying to learn some more stuff and save some $$.

 

no you didnt, the fuel will only come out when the truck is being cranked.

 

OK - we tested again - actually cranking the engine and we had fuel exiting the fuel filter - so that means the lift pump is working, correct?
So I guess the next test is to remove one of the injector lines (the one on the passenger side has been suggested) and see if diesel comes out of that injector line.
Been told this should spray and to have a rag handy to catch the spray and to cut the engine quickly. Also to then clean up the connection when you replace the line.

Also been suggested to pull fuel from the water/air brass fitting in the front of the engine?

Thanks for any comments, corrections etc