I just installed my FASS 150 and finally got my fuel pressure gauge working again. (The guy before me had it rigged up odd.) While idling/ driving normal my fuel pressure will move 1-2psi or so very quickly back and forth. When I turn on my comp box and get on it a little I goes freaking nuts. It jumps back and forth between 14psi-24psi. I have heard that sometimes this can be caused by having too big of a pump. My injectors are stock until i find time to install my 150hp nozzles. I am just wondering if what I've heard is correct and the bigger nozzles will help at all. All information is helpful, thanks.

 

is the gauge electric or mechanical ? if it is electric do you have a fuel pressure snubber ?

 

It's mechanical. The guy before me tied the line in right at the injection pump with a fitting and some 3/8" hose. That hose ties into like a metal saucer thing with a rubber diaphragm in it, then a line runs directly to the gauge. Sorry for the terrible description but i've never seen anything like this haha. The metal thing has a screw so i can bleed all of the air out before the diaphragm which is what im going to do tomorrow. If it helps at all the engine doesent surge with the gauge but when I open my door i hear the pump kicking on and off with the pressure fluctuations.

 

I dont believe your pump is supposed to turn on and off, I would be curious to see if it is a bad pump or something in the wiring. My fass is on at all times while the truck is on

 

Sounds like what is happening is the water hammer effect. Water hammer will affect both mechanical and electric gauges. Use a needle vavle for mechanical gauges and a snubber for electric gauges. Here is a couple links with more info and how to fix it.
Mopar1973Man's Dodge Cummins Articles - Fuel Pressure Gauge And Water Hammer Effects

Mopar1973Man's Dodge Cummins Articles - Gauges

Hope that helps you out.

 

Put a needle valve in the line to the gauge.
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