Last night it got into the 40's and on my way to work my fuel pressure stays 5 psi and creeps down to 4 psi. Im am running 2 stroke oil. I wouldnt think that I would need to run thinners already even with the weather in the 40's. I still have a dealers warrenty. My fear is that there gonna put an intank pump. Or should I just replace the whole fuel system with a FASS?

 

Return fuel warms the tank pretty darn fast.
Unless you are short tripping it my opinion is the weather has nothing to do with your lower pressure.

 

I had the "in tank" pump put in by the dealer just before having the vp44 installed by the dealer. I as you was skeptical of the "in the tank" lift pump. I then installed the "big line kit" getting rid of ALL the banjo fittings and running a 3/8 fuel line directly to the new vp44. this all happened in May of '06 about 10,000 miles ago. Since installing the "big line" kit my fuel pressure runs at 7-9 psi this is all the time even at full throttle climbing mountain passes with my 5th wheel. After the dealer first installed the "in the tank" lift pump my fuel pressure would fall to almost 0 when I really got on it. only after installing the "big line kit" did my pressure remain constant. Getting rid of all the banjo fittings seemed to be the key.

 

Yea im gonna be doin the same. But I figured if im gonna do it might as well do it right with a FASS kit for future mods.

 

When it gets down to -15 to -20 F I've seen the fuel pressure down at 1-3 for quite a long time. It really bothered me the first time. The truck would not warm up just idling. I finally got to where I could plug the block heater in and it started warming up. At least it got off the peg. As it warmed up the fuel pressure came back up about 12. After about an hour I took it on the highway. It took another hour for the pressure to get to 14 normal. I try not to let the truck soak at -15 for more than 8 hours even if it means a midnight cruise for an hour. It starts a lot easier too.

The fuel does not gell but it surely gets thicker or more viscous. I always use a healthy dose of white PS too, even though our fuel is winter graded.