Ok so three weeks ago about 1500 km's I replaced the IP in my 01 24V, and WOT on the highway it would drop to around 11 or 12, well this morning I saw it drop as I left the farm to under 10.

It was cold mind you close to freezing, it was at 2 degrees Celsius or about 35F.

Can the cold make this kind of difference, to fuel pressure, or do I have a brand new IP going out again.

 

I think you're referring to your "lift pump" or transfer pump. Your injection pump makes a wee bit more than 12 lbs. If this is your case, I doubt 35 degrees would cause your pressure to lower. I'd keep an eye on it. It's not uncommon to see a new pump quickly fail after installation or even be DOA.

 

Yup your right LP not IP that was a clear typo on my part, also in the wrong forum

 

Down here in New England during the winter months my Fuel Pressure reads lower and rises as the truck warms up.

 

My truck seems to create a vaccume in the tank so when I am on long road trips my pressure will drop from 13 to as low as 9 pounds until I stop and fuel up or at least release the fuel cap. You can hear the vaccume seal when you open the cap.

 

My LP pressure is 1 to 1.5 psi lower cold until the fuel warms up too. I thought my lift pump was wearing through the winter but as the weather warmed up, my LP pressure returned.

 

There is a vent on the top of the tank. it is similar to the vent on the diff breather. Clean it off, and you shouldn't have that problem.

 

I clean this vent opening periodically. I can tell when it's clogged because after I shut the truck off you can hear it whistle for a long time. I crawl under there and stick a nail through it. But even after I do that i still have the vaccume when I release the fuel cap.

 

That kinda makes me wonder if a bee built a nest in it or not. The vent is supposed to vent your tank. Maybe if you gave it a quick shot of carburetor cleaner w/little red plastic line...use some goggles or a face shield, that stuff goes straight for my eyes every time I use it. It'll even go for my eyes if someone else uses it.

 

I thought about just making the hole a little bigger, but I'm afraid of what may get into the tank. Keep in mind that this is a farm use truck. With as dry as it's been for a long time now it sees alot of dust and driving through the weeds. I use a pair of panty hose over my air filter as a pre-filter other wise it's due for a cleaning every few months. With this I just brush off the big stuff and truck on.