so i have retro fitted a tbi setup on a '85 chevy blazer, and am using an external adjustable fuel regulator. what's happening is the colder the motor temp is the higher the fuel pressure. as it warms up it drops till my setting of 14 psi. i need ideas why the fuel pressure starts high and then drops slowly as it warms up....

 

Liquid filled gauge under the hood? If so it is the gauge, not the fuel pressure. The liquid expands as it heats up and puts additional pressure on the Bourdon tube, thereby displaying a lower fuel pressure.

RBob.

 

yeah i have noticed mine does this too. ugh. i need a higher pressure pump anyway. according to my gauge im getting barely 10.5 lbs..

 

i bet your absolutely right!!! liquid filled gauge and under the hood, yep. so when its hot and saying 14 psi, its probably less in reality? set the pressure when its cold and forget the gauge when its hot?

 

set when cold and forget when hot. And what he is saying is if its showing 14 its actually more

 

What UnderCover said... Set it cold and don't look at it when hot.

RBob.

 

Took me about 3 years to pound this into Kurt's (OldRed95) head, but finally was able to.

 

Indeed, my Autometer liquid filled gauge info states about 1psi for 30*F change,
it has a pressure equalizing/liquid filling port.

Setting the pressure cold won't work either, remote mounted Bourdon tube or electronic transducers (I use both) will also show a drop, as the rise to normal operating temps affect pressure.

The solution is to NOT use an underhood gauge, liquid filled or otherwise.

Most Bourdon tube gauges state 140*F as an upper limit.
&
Check & set your fuel pressure at operating temp with the proper equipment.

A gauge like this will correctly reflect the warm pressure drop.
http://www.amazon.com/Actron-CP7817-.../dp/B0006V2BK0

Electronic gauge & sender can cost $200.

Shop around for the best price/equipment to suit your needs.