For the past 3-4 months I have been fighting with this problem, some days the stumbling is very bad and other days you cant make it do it. I started with a fuel filter change - didnt help. Two nights ago I put in a new lift pump and it ran perfect for the next day, I thought that I had it then! Then last night on the way home I was passing a car on the highway and it was missing/stumbing so bad that I had trouble getting past the car. Once I let up and maintained highway speed it was good again.
I tried opening the filter drain line (brass valve on top of the thermostat housing) with the truck running, nothing came out and the truck died, but with the engine off and truck in gear, I can get good flow/pressure out of this line when I engage the starter to get the lift pump to run.

The OPS was changed less than a year ago - could it be bad again? I dont have a relay on it.

What kind of pickup is in the fuel tank? Is there a screen in there that could be plugged?

What about the fuel cap, can it get plugged and how do I check it?

PMD?

Thanks in advance
Slapshot

It does seem the OPS has quit and is not powering the LP after the engine starts.

Coming soon:
http://dieselplace.com/forum/showthread.php?t=22860&page=1&pp=10


http://dieselplace.com/forum/attachment.php?attachmentid=1710&stc=1

As per usual John clean looking kit, let me know when they are available

What are we looking at here John?

Pump control ckt. Description of the function is here:

http://www.kennedydiesel.com/detail.cfm?ID=324

Wow, that looks like an excellent unit. It will work for both Duramax and 6.5?

Also thanks QM for your diagnosis of my problem, I probably have a good used (spare) lift pump now.
I will pick up a new OPS sender and a relay tonight.

Is there anything else I will need for supplies to wire in the relay? Connectors? Splices?

Newbie Question
Instead of paying shop rate to change my OPS, I decided to try to do it myself, I feel silly here but I cant find it.

Help!

Also, the relay I bought doesnt have the terminals labled like in the instructions, they are numbered. Can anyone offer any insight into that as well?

Slapshot

It's behind, below, and slightly to the right of the fuel filter. Pull the two bolts that hold the fuel filter in place and hold the filter to the side to give yourself more room to work on the OPS.

It's easy, just take your time.

Takes a special socket to remove Napa carries it as do others