Weird fuel pressure

[DartVadar]

Ever since I've broken in the cam on my new motor the fuel pressure has always read about 1-3 PSI cold or hot, and sometimes it doesn't even read at all. But it occasionally reads about 8. This is an edlelbrock mechanical fuel pump on my 360 btw. At first I figured the gauge was the problem considering I had good fuel pressure when I first started the engine. I also find it odd because the engine runs perfectly, its never stalled, hesitated or surged, starts easily, even after sitting, so there are no symptoms that would indicate low fuel pressure. The fuel pressure gauge is after the pump and filter, the filter is in a aluminum case so I can't see if its clogged or not.

Is it possible that there is some crud that is restricting flow to the sender in the fuel tank? I never fully cleaned the tank, I just flushed it out. What are the odds that I either installed the gauge wrong or I had really bad luck and found another inaccurate gauge? Or is it somehow running good with low pressure?

 

[EL5DEMON340]

If the gauge is in the engine compartment and is liquid filled it will be all over the place ,

 

[DartVadar]

If the gauge is in the engine compartment and is liquid filled it will be all over the place ,

Its liquid filled, and in a little hole before the dual carb feed line, so right above the intake manifold, and yea it kinda moves around, its never been steady. So liquid filled ones are no good?

 

[67Dart273]

If the gauge is in the engine compartment and is liquid filled it will be all over the place ,

No idea what this is supposed to mean

The whole idea of a liquid gauge is to stabilize and dampen the movement. The insides of a gauge are actually pretty precision and delicate, like a watch. Constant pounding from some source that beats them to death will..........beat them to death

Not only that, but the tube (bourdon) that "makes them work" is essentially a piece of copper / brass tube that the pressure is trying t o straighten. If you pound it enough, it will "work harden" rendering the gauge useless and inaccurate

 

[DartVadar]

No idea what this is supposed to mean

The whole idea of a liquid gauge is to stabilize and dampen the movement. The insides of a gauge are actually pretty precision and delicate, like a watch. Constant pounding from some source that beats them to death will..........beat them to death

Not only that, but the tube (bourdon) that "makes them work" is essentially a piece of copper / brass tube that the pressure is trying t o straighten. If you pound it enough, it will "work harden" rendering the gauge useless and inaccurate

So could I have ruined the new gauge already? or is it just not reading accurately because of its location? Never realized they were such precision gauges, pretty neat.

So what could be the cause of this low pressure reading?

 

[EL5DEMON340]

The heat changes the reading, like what heat does to oil thins it cool off a bit thickens it.

 

[EL5DEMON340]

No idea what this is supposed to mean

The whole idea of a liquid gauge is to stabilize and dampen the movement. The insides of a gauge are actually pretty precision and delicate, like a watch. Constant pounding from some source that beats them to death will..........beat them to death

Not only that, but the tube (bourdon) that "makes them work" is essentially a piece of copper / brass tube that the pressure is trying t o straighten. If you pound it enough, it will "work harden" rendering the gauge useless and inaccurate

Here's what it means 67dart right from Aeromotive

"we do not sell a liquid or oil filled gauge due to their extreme sensitivity to temperature, i.e. when a liquid filled gauge warms up the liquid expands and pressurizes the case internally. This creates the illusion of falling fuel pressure, i.e. the gauge reads lower and lower pressure as it gets hotter and hotter.

Selling a dry gauge eliminates the pressure fluctuations on the gauge needle caused by temperature, but unfortunately, a dry gauge is more prone to damage by engine vibration. We recommend that you use the Aeromotive gauge for a reference when you are checking fuel pressure, but that you then remove it in order to prevent damage."

 

[67Dart273]

Here's what it means 67dart right from Aeromotive"

Thanks, temperature is all you really had to say........................

"All over the place" would be my description of a non-liquid gauge, LOL

 

[74Dusted]

Thanks, temperature is all you really had to say........................

"All over the place" would be my description of a non-liquid gauge, LOL

I'm pretty happy with my Non-Liquid Filled Gauge on my 6-71 Blown '73 340 Duster.

I have it mounted to the side of the rear carb (so I can keep an eye on Fuel Pressure while driving), and even with the heat of the blower and the vibration (solid motor mounts) the gauge only fluctuates about 1/4 - 1/2psi

 

[famous bob]

I'm pretty happy with my Non-Liquid Filled Gauge on my 6-71 Blown '73 340 Duster.

I have it mounted to the side of the rear carb (so I can keep an eye on Fuel Pressure while driving), and even with the heat of the blower and the vibration (solid motor mounts) the gauge only fluctuates about 1/4 - 1/2psi

pull the little rubber plug out and drain the oil out of the gauge, reinsert plug, will work just like a dry gauge!---bob

 

[nm9stheham]

I've seen a couple of cases of these mounted on race engines and they were grossly inaccurate. Not sure if it was the heat of the vibration. As a race tech inspector, I made guys take them out of these on-engine locations; it's an easy part to have break and have fuel spraying all over, and very uneecessary to have on all the time.... in a locaotin where you can't see it. If you want to see fuel pressure regulary, then use a remote sensing electic type.