Rail loosing pressure while towing and WOT

[PDW Power]

I'm not much for help when it comes to Duramax so I thought I could get some input for a friend of mine with a 2001. I'm going to first start with a description of his truck.

2001, Auto, FASS, Brand New Stock Injectors, Power Pup...with a weird fuel problem that I couldn't make sense of.

This is second hand info from another Dodge enthusiast, so bare with me.

While towing a 20' stock trailer up grades he looses 5K+ PSI on the rail which throws his truck into a limp mode. After shutting down and restarting he'll get another 100' up the grade and it starts limping along again. He gets a code that was explained to me as “large volume fuel loss.” This problem happens at 2 different times. WOT with no trailer and pulling a grade with what I consider a rather light trailer. At no other time will he have any problem with the truck. He's disconnected the Pup and replaced the fuel filter 3 times. He's not loosing fuel on idle and has replaced all of the fuel lines from tank to rail, nothing is pinched either. I'd like to recommend something else and without knowing the ins and outs of the Duramax this is where you all come in. If you can help I appreciate it. If you can't thanks for reading anyhow.

 

[JOHNBOY]

Will it hold pressure with the stock tune? I mean no more power pup. Has he checked the pressure from the Fass? Should be no less than 5psi no more than 10psi. Idles smoothly? No lope or rattle? How is he monitoring rail pressure? Tech II, EFI? Does he have a pressure box? Like a TS MP8 or PPE maximizer? People tend to forget about pressure boxs. I had a buddies truck that would not hold rail pressure no matter what I did. He told me his Maximizer was disconnected it was not. With a pressure box connected your rail pressure readings from the ECM are meaningless because the box skews them trying to make power.

Just off the wall is his trans stock. Any chance maybe he is limping it?

 

[PDW Power]

Will it hold pressure with the stock tune? I mean no more power pup. Has he checked the pressure from the Fass? Should be no less than 5psi no more than 10psi. Idles smoothly? No lope or rattle? How is he monitoring rail pressure? Tech II, EFI? Does he have a pressure box? Like a TS MP8 or PPE maximizer? People tend to forget about pressure boxs. I had a buddies truck that would not hold rail pressure no matter what I did. He told me his Maximizer was disconnected it was not. With a pressure box connected your rail pressure readings from the ECM are meaningless because the box skews them trying to make power.

Just off the wall is his trans stock. Any chance maybe he is limping it?

He is getting the same results with stock tune. Pressure gauge was T-d off the feed line, pressure reported as ok (not sure what psi). Stock idle. No pressure box, he's only running the Pup. I'm not sure of how he's monitoring pressure. 100% stock tranny, that is a possibility with the pup removed his truck is stock...IMO there should be no reason the trans can't hold. Thanks for the reply. He's thinking about buying a 6.7 and i know he can't afford it so i'm trying to get this straightend out for him.