The last few days, my fuel pressure gauge has been bouncing alot more than usual. At idle it usually bounces from 4-5psi. The other day it started bouncing from 3-6psi. Today at low rpm driving its bouncing from about 2-6psi and occasionally goes 0-6psi. What would make it do that???

 

Do you have a snubber in line?

 

A gauge "snubber" will prevent the lift-pump pulses from flinching the gauge-needle.

The only place I have ever seen snubbers available is McMaster-CARR.

Although they have one that is rated for fuel and light oils, it is better to go up a few notches and get the one for "air and other gases".


That being said, a snubber is not a lifetime solution; I have found that they are good for about six years with a diaphragm lift-pump and only about a year with a piston-lift-pump.


Starting at the gauge-port in the fuel-system, I put first in line a 1/8-NPT ball-type cut-off valve with the valve just barely open; then, I have last years old snubber to absorb the brunt of the pulse; then, this years new snubber to quelch the rest of the needle flinch, to which connects the pressure line that goes into the back of the gauge itself.


When you order a snubber, you may as well get a dozen, as they don't last forever.

 

Check valve in pump staying open possible spring broken or weak.

 

All you have to do is let air into the pressure line. If its full of fuel it will see every pump, but the air will buffer and compress these spikes and give you a smoother reading. Mine was very steady after I did this and should work for you.

 

Thanks for the comments. I have a valve mounted at the banjo, It was listed as a "snubber valve". Maybe it gave up. I believe Glowshift sells banjo snubbers. I might get a couple.

 

^^^ This makes good sense. ^^^

I have noticed that a recently molested gauge is a lot steadier than one that has been in use for a few weeks.

 

Lift pump or injection pump? Please dont say injection pump, that things been rebuilt 3 times in the last couple years...

 

I have the snubber but sooner or later the fp gauge starts jumping again, I have searched for a better gauge but nothing that will solve the problem permanently yet. I would also like to know of a better option.

 

I kinda am led to believe that the needle flinching problem is why they have liquid-filled gauge faces.

Surplus Center has a big selection of liquid-filled gauges.

Does anyone know if the liquid-fill does indeed absorb the fluctuations ??

 

Liquid fill gauges will help. what you are calling a "snubber", is that the same as an isolater? Randy.

 

NO; a snubber permits the product being monitored to pass through the snubber and on to the gauge; whereas, an isolater is a liquid-filled line that connects between the gauge and whatever is being measured, thus isolating the gauge from the fuel in our case.

Isolaters are often filled with anti-freeze, although other liquids are used as well.

In my opinion, isolaters are detrimental to the accuracy required to monitor variances in the relatively low pressures of a fuel system, where a single PSI can mean the difference in NORMAL and a filter starting to plug or a pump getting weak.

 

Years ago I ran a isolater/liquid gauge on a big rig; NTC-400 cummins. Never had a problem with needle fluctuation,but as you say,I was at a higher PSI <100 at cruise up to 350 PSI Max.

 

The purpose of the glycerin in a liquid filled gauge is to dampen the pulsations and to protect the mechanism from damage while operating in a corrosive environment.

The bourdon tube, gears and pointer are immersed in viscous glycerin and slow down or dampens the pointer as it now has to move through the viscous liquid.


Bourdon is not to be confused for Bourbon

Here is a 2 5/8" liquid filled fuel pressure gauge.



Some have also used a section of high pressure hose between the rigid tubing and the tap on the fuel filter to act as a snubber, a grease gun hose will work.


Or you can use an Electric Fuel Pressure gauge, this would be more accurate in my opinion.



Instructions.

http://www.autometer.com/download_instruction/783h.pdf

Jim

 

I just got a suggestion. If i was to connect a "T" fitting inline and run a capped line upward with air in it, would that help dampen the pressure? They do that with house plumbing sometimes.