Diesel quits running

[Pault]

I have a 97 GMC 3500 with a 6.5 turbo diesel. At times it will just quit running. It will run fine for days and then for no apparent reason it will quit running and wont restart. After it sits around for a couple of days it will finally restart, run and start fine for a few morre days, and then repeat the cycle. I have had a mechanic check it out. He replaced the fuel filter and fuel pump, but it still has the same problem. I suspect an intermittent electrical problem that causes the fuel pump to stop working. I have replaced the fuel pump relay, and checked all wiring, but still cant find the problem. If any one has any suggestions, I sure would be grateful for the advice. My email address is gcea@juno.com.

[Mark Rinker]

Search this forum for entries containing FSD or PMD. FSD stands for Fuel Solenoid Driver, PMD stands for Pump Mounted Driver. They are the same thing - a little black box mounted to the side of your IP - injection pump.

Most people on here have replaced this componant at least once in their trucks life. Most mount a new one on a heat sink, rather than back on the injector pump. Its easier, and the goal is to reduce heat from the electronic componant to increase its longevity. Heat kills.

Happy reading.

[Pault]

thanks so much. I'll replace it and see what happens.

[moondoggie]

Good Day!

Like Mark says, classic FSD/PMD symptoms. I think the best bet is to get an extension harness & mount it in front of the driver-side battery, or go with Heath's unit.

"He replaced the fuel filter and fuel pump, but it still has the same problem." Did he actually determine if the LP* was defective or not? Your truck should run fine even if the LP is dead or not getting power. The most common symptom of a failed LP system is a miss under load just like a gasser with an ignition miss.

"I suspect an intermittent electrical problem that causes the fuel pump to stop working." If it were me & I had to know, I'd go to the boneyard & clip the wires to the LP, before & after the LP. That would give you both connectors, so you could make up a jumper that would add two wires to be temporarily strung into the cab. You could then connect a small 12V lamp to the two wires. Be careful troubleshooting this way, I think the PCM in trucks after 95 might be switching the LP on & off; earlier trucks like mine powered the LP through the OPS whenever the engine is running. As I said, however, I highly doubt your LP has anything to do with your symptom.

Be careful of terminology: there are three fuel pumps on your truck, the lift pump, a fuel pump built into the injection pump (which is why it'll run without the LP), & the injection pump itself.

It was nice of you to include your email address, but keep in mind: if you troubleshoot outside these forums, the only person that profits by your new-found knowledge is you, the rest of us will never know what you did & what fixed it. When your troubleshooting is done in the forums, all of us gain your knowledge. It's what's allowed a poor mechanic (me) to keep my trucks running.

Blessings!

*LP = Lift Pump