2smoke4ever

I have an 01 with glacier fuel boss lift pump. Truck has 195k, had lift pump for 10 yrs. Recently out of nowhere the fuel pressure will drop to 5 psi from 15-17 for no reason under normal running. Replaced fuel gauge, isolator, lift pump, return fuel flow valve on vp44, replaced pressure regulator, installed fuel sump on tank, no results, same symptoms. No codes for vp 44 or anything else for that matter. Thoroughbred diesel told me the problem is not my vp44, and to check camshaft sensor, crankshaft sensor, or ecm, possibly a bad ground. This has been going on for two months now, truck still runs fine, good power, no rough idle or excessive smoke. Any help is appreciated, I'm about ready to go nuts. Fuel pressure will drop and then return to normal only to drop again for some reason.

AlpineRAM

My take on this would be trying to determine if it's a true fuel pressure fluctuation or a gauge fluctuation- of possible I'd get a cheap fuel pressure gauge (preferably mechanical) and jury-rig it to get some readings. (read duck tape to the windshield)
This can reduce the $ for parts you throw at it..

2smoke4ever

I did tape another gauge to my windshield wiper, it was a mechanical oil pressure gauge tapped directly to the vp 44 inlet(no isolator). The fuel pressure fluctuated just the same. Gonna clean all the ground wires, and go from there. Thanks.

KATOOM

Interesting that you found the mechanical oil pressure gauge did the same thing as your mechanical fuel pressure gauge... So knowing that, what grounds are you wanting to clean up and why? What do you think is going on to cause the 10 psi drop in pressure?

Question I have is, does this happen while driving or idling? Are there ANY noticeable running conditions which would coincide with the pressure drop? Like the engine sounds different or runs different... And how long does the fuel pressure stay low before it returns to normal?

AlpineRAM

OK, with that question answered-
since the glacier is a mechanical system it should not depend on grounds to deliver fuel pressure while the engine is running.
I assume you checked the belt- so it can either be an input restriction or break, or a defective pump or a sticking regulator.
With all that you replaced I think it may be the line from the fuel tank to the pump..

SIXSLUG

Fuel line? Is it rubber? Could it be getting sucked down to a restricting point. Are you pushing or pulling fuel? Just a few shots in the dark.....