Does anyone know why it seems like rail pressure is lower when the temp is colder? Does the the ECM cheat it back because of sensor readings? Or is there something else going on?

What's you lift pump pressure like?

I havnt got around to getting a fuel pressure gauge but its on the list:smart: But as far as I know it seems fine. It just seems when it is cold the rail pressure is lower.

On my truck, whether it's cold or hot out, idle RP is around 6500PSI. The '03-'04's should be about 5000psi IIRC.On cold start up, my trucks RP is actually "HIGHER" than at normal idle RP.As said earlier, check your LP first. Then you should probably check your fuel filter/filters. If those are good, check your FCA.Could also be IAT sensor or a weak CP3.Any codes????How many miles on the truck???

I just changed the fuel filter this past weekend. I dont think there is necesseraly a problem or anything because I remember that is did this last winter but I just thought id ask. I didnt know if it was similar to egts and in colder weather you would see a lower value. Anyways I know off hand that mine idles at 5000 but I will have to wait till it cools off again to see what it is when im driving, Im thinking that it might be under 10000 at highway speed. I almost forgot but no there is no codes and it just hit 110,000:lol:

I just changed the fuel filter this past weekend. I dont think there is necesseraly a problem or anything because I remember that is did this last winter but I just thought id ask. I didnt know if it was similar to egts and in colder weather you would see a lower value. Anyways I know off hand that mine idles at 5000 but I will have to wait till it cools off again to see what it is when im driving, Im thinking that it might be under 10000 at highway speed. I almost forgot but no there is no codes and it just hit 110,000:lol:

Is your truck an '04 or '04.5???? If it's an '04, 5000psi at idle is perfectly normal. The '04.5+ idle at 6500psi. Plus or minus a bit. To maintain 65mph in my '04.5, I'm running about 16-17,500psi RP. That's normal.

It is an 04 and I usually see 15 or 16000 driving. Also I thought of another question on the engine tags on our trucks it says the fuel rate at advertised hp. What controlls the fuel rate the fca? My fuel rate is lower since I unfortunally ended up with a cali spec engine.