First, I want to say thanks to everyone on here. I picked this truck up non-running and after a couples of days of reading on this forum I was able to successfully troubleshoot my motor and get it running flawlessly (for about 4 hours, LOL).

A little history:
The previous owner apparently didn't know how to take care of the truck. He let the air filter clog and kept driving it until he finally clogged the catalytic converter. He replaced the air filter but had no idea about the Cat. After 2 mechanics gave up troubleshooting he finally parked it and let it sit for the last 8 months. I found him trying to get it going again last week, we talked a bit, and next thing I know, I'm the proud owner of a non-op chevy 6.5l.

After troubleshooting the truck I finally found the clogged Cat. I cut it out and ran a bypass temporarily today(Sunday) until I could order a new Cat on Monday. When it first started up I was thrilled. There is nothing like that sound. It was surprisingly smooth for a truck that sat for 8 months.

I drove her around the rest of the day and suddenly it happened, the truck began to accelerate (on it's own) for a few seconds (and smoked). I pressed the pedal a few times and regained control (smoking stopped). Not sure if I did it or it just fixed itself. When I stopped at a light it seemed to idle fine, but then it bucked, kind of like a misfire. It did it twice at the light. I continued heading to the house. It surged again ( a trail of smoke), accelerating 5 mph over the speed I was traveling, but when I hit the brake it dropped down to idle and I was able to push the peddle and resume my normal speed. Then it began to intermittently surge a couple of seconds at a time ( some haze but not much smoking). When I reached a light it misfired several times. Progressively got worse as I drove. I finally got home and parked it.

After about an hour I went out to move it into the driveway to take a better look at what was going on. When I started it the truck immediately began to rev up (3500 and climbing, huge cloud of smoke). In a panic I shut it off. I popped the hood and checked to see if something was disconnected but found nothing. I started it again and it surged between idle and about 3000 rpms several times (a second at a time) and finally settled into an idle, but when I pressed the peddle it began to surge again (Still smoking).

Things to NOTE:
Replaced all fluids once I got her running initially.(Fuel, oil, radiator, trans)
New Air filter, oil filter and trans filter.
New Batteries.
Did not replace fuel filter.
Tested LP and LP Relay (Crank and OPS), OPS (operating as specified), glow plugs, EGR, grounds
Air Bags have been disabled (Light flashes 7 times, not sure why this was done)
There are no codes.

I plan to begin troubleshooting my new problem tomorrow but I'm not even sure where to start.
I was planning on looking at the following but any advice is welcome:
1. Fuel Filter is all plastic and covered in fuel (might be leaking). Was going to replace with Delco filter.
2. Check return lines for bubbles. (If fuel filter is leaking, should I expect bubbles?)
3. Return lines seem very loose fitting. (doesn't seem right, they pop off with a touch. Will buy new tubing and clamps)
4. Check ground wires again.
5. Still have a replacement PMD from my first troubleshooting exercise (old one on truck is still working, so I left it), but it sounds like this is not a PMD issue. Will swap anyway just to be sure.

Oh the joys of new ownership on a well used old truck.

I look forward to feedback.

 

By what you are describing, my first guess would be the PMD.

 

X2 on the pmd mine started doing this today

 

Well, now I'm not sure what to make of it. After I got home from work, I started her up and she ran great. No hiccups no overspeed, no smoke. Drove it about 45 minutes before heading back home. I'm going to have to drive more to get it to fail I suppose. I'm thinking the problem is heat related, which works well with your thinking it is the PMD, since it is cooled by the fuel in the IP and probably takes much longer to heatsoak the transistors than the rest of the motor.

Went ahead and replaced the return lines. I don't see any bubbles so I assume it was due to the poor fit of the old lines.
Replaced the fuel filter and it fits much better with no leaks.
All of the grounds appear to be tight and clean.

Since the PMD is probably still fine and the problem is most likely a lack of thermal transfer due to age and fatigue of the thermal material, I wonder if I could reuse the PMD for a remote setup? Will be ordering one tomorrow. Any recommendations on the best PMD remote kit for the price? I have found so many and the prices vary drastically for what appears to be very similar. Based on discussions I've found it appears the bumper placement is the most accepted practice. Does this sound fairly accurate?

Thanks again cviola2005 and Mayhem for your input. It's always nice to know someone is willing to put up with my longwinded typing.

 

The bumper location seems to be where the majority of us 6.5 owners seem to relocate to mine has been on the firewall for 3+ years since purchasing the my truck allthough I will relocate mine to the bumper as well ,as for pmd's I would stay away from anything that is remanufactured and try to get the largest heat sink as possible good luck i hope you enjoy you're truck as much as I enjoy mine

 

You were dead on. I purchased a new Flight Systems PMD and a remote kit, mounted it to the bumper on drove 300 miles this weekend without even a hiccup. I checked the temp of the PMD after a long run and it was barely warm. Thanks for your help.