Alpine951

I recently purchased an analog fuel pressure gauge with the correct size fitting that screws right onto the end of the fuel rail. I just put an adjustable FPR on and when the car is idling or revved the fuel pressure dithers rapidly between a 10 psi swing. The needle moves so fast it is a blur. Is this how it should be or should it stay right on a specific pressure? I am not 100% sure if it did the same with the 3 bar fpr that was on there before but I will probably put the 3 bar back on to see if it dithers rapidly as well.

Tom M'Guinn

They tend to do that (mine does) especially with big pumps and injectors.

Alpine951

I have the stock pump and stock injectors. When I look on youtube for fuel pressure tests every one I see the needle does not rapidly dither all over the place. It just stays at what ever the pressure is. Can someone else confirm that the gauge should dither? If it is supposed to dither then does that mean the highest of the swing for a 3 bar fpr should be 43 pounds even though it rapidly dithers back and forth from 33 to 43?

Tom M'Guinn

BTW, not saying it "should" jump around, just that it's common with typical cheap-o gauges... I think the mid-point is probably the best bet...

See references to it in these threads....

https://rennlist.com/forums/944-turb...ng-normal.html

https://rennlist.com/forums/924-931-...ail-broke.html

Alpine951

What's a good gauge that works better and what adaptors do I need to screw on to the fuel rail?

eman930

You need a fluid filled gauge, the non fluid ones will bounce around when the engine is running

eman930

Buy here, select a the liquid filled gauge

http://www.lindseyracing.com/LR/Pors...-FPGK-944.html

zerMATT951

My Autometer gauge from LR doesn't move at all. It is rock solid at 43psi no matter what RPM and I'm running 80# injectors with the Bosch HV fuel pump.

TurboTommy

Mine is fluid filled and dithers as well.

Crackership

Mine too.

Alpine951

So I ordered the LR one. We'll see what happens.

eman930

Id think if its still doing it, Check you fuel dampner

968 GUY

I was going to suggest the damper as well.
My gauge, which I have not installed yet, is fluid filled but also has some sort of adjustment screw at the fitting on the back of the gauge, which if I remember correctly is for dampening. Sort of like a needle valve. It's at my Dad's place, so I can't look right now.

cheapmods

is it just your run of the mill fluid filled 100psi gauge or is something special about it? is the nipple on the back? 1/4"? compression or NPT type threads?

968 GUY

@ cheapmods. If you were asking me, in my post I stated that I am not able to take a look at it right now, but I may have bought it from Summit at their ebay page.