First I would like to say I am glad I found this site! I am new to diesels and need all the info I can get.There seems to be a lot of knowledge here,maybe some one can help. I am having some issues with my truck I cant figure out!

I put a Vulcan big line in with a new stock lift pump, got 9 psi at idle, 7 under acceleration. The pressure started to drop to 0 and stay there for a while then go back to normal,but when I start it will always have pressure then nothing. I just put a 4601 pump in and now the pressure stays up but only 10psi,8psi. I checked the isolator the gauge,line. I am wondering if the vp44 has some thing to do with it. I am getting the dreaded 0216 code, but the truck runs perfect. I only get the dead pedal when its cold for the fist 5 minutes or so then she runs perfect. Does the vp44 have a check valve that may be stuck ?
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VP has a overflow (check) valve on the return line, although this won't affect fuel pressure going in like it does on the 12v's. The VP has an internal pump, which provides enough pressure to overcome the OFV. This is also why these trucks can continue running with a dead LP.

Where do you have your gauge plumbed in? After the fuel filter is best. You can monitor the condition of it by the pressure drop. With that said, how is your fuel filter? Are there any kinks in the new hose you put in? Do you have another gauge to verify that yours is correct? Just at an idle should tell you if your current gauge is accurate.

 

How can the bypass valve, set at 17 psi (on a stock VP), not affect the fuel pressure at the inlet? Isn't the whole idea of the bypass valve to control the FP at a level suitable for VP?
I read and re-read the factory manual and the only way I can see for FASS and Walbro to get FP to 26 psi and more, is to provide so much fuel flow that the VP bypass can not handle it and more pressure builds up with a wide-open bypass.
-P