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I just want to help solve the problem. There are several possibilities, and doing a valve shim is not the easiest thing to do (and easy to screw up), so just trying to avoid "lawn dart" approach, and narrow down the cause, before proceeding.
 

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i appreciate all the help and info you guys got me allready.i'll try to narrow my problem down to a more passific thing.thanks again.ps i scanned for codes but it didn't have any codes.
ok, no codes.

Oddly that does help. The dmax is prone to laydown under high fuel loads. Some FPRV's will 1093, and others do not. Mine has fallen into the latter category.

My symptoms are as follows: Under a WOT load, as the rpm approaches higher levels, the truck just seems to give up, and the rpm fades back, with a lack of power. When I completely unload it, the problem has dissappeared, and I can just go on my way. Elusivity.

Does this sound familiar? Or does yours stay in a limp mode?
 

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I am satisfied you have an FPRV popping. The fuel pressure regulating valve. Except for one thing. it normally resets itself, as it is purely mechanical. However, if you had a code 1093, you would be in limp mode until it was cleared. Reprogramming would normally accomplish this, as most box protocols clear codes automatically.

if you're standing in front of the truck looking at the engine, its to the right of the turbo, The fuel rail is easy to see, its like a big long round cylinder, runs front to back about 1.5' round. The FPRV is on the END of the driver side fuel rail, closest to the rear of the truck.

Look HERE for some pics.

When you locate the valve, it is a bugger to break it loose. Use a very high quality 18 mm (IIRC, or it might be 19 mm, was an uncommon size) offset wrench or a 6 point socket (don't use a 12 point). You don't want to round off this sucker, or you will have to pull off the fuel rail. Be patient, get the right tool, with some extra leverage, maybe a pipe, or another breakover tool. BE PATIENT. Don't torque on it, until you are sure you can, without it slipping off the end. A helper might be useful.

Once you get it off, it is time for a trip to ACE.
 
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