Fuel pressure gauge question

[Layne02]

I put an inline fuel pressure gauge on and its jumping like crazy, someone said it is because I have mechanical pump. If thats true , why is that?

 

[1987 GMC Jimmy]

I haven’t put a gauge on a mechanical pump setup, but it makes sense. The electric pump uses an impeller thats always spinning, and the mechanical pump uses a back and forth mechanical actuation to push down and release a lever that controls a diaphragm. It’s like pumping up a bicycle tire. You can’t consistently apply pressure because you have to release plunger to get another pump stroke in there to continue pumping more air in. The cam eccentric just spins a bunch faster than a person pumping up and down to air a bike tire.

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[Layne02]

Thats exactly what mine is doing, Id like to know what the pressure is , may put a regulator between pump and carb

 

[Snoots]

It would seem to me that you would need a liquid-damped meter movement for a mechanical pump but, shouldn't a backflow valve before the gauge prevent this?

 

[Honky Kong jr]

It’s because of the pulse and that gauge is pretty much trash now......ask me how I know. I’ll tell you I’ve been there done that. A liquid filled gauge will curtail some, but not all a regulator may help but the bouncing needle is an evil of a pulse pump.

 

[Layne02]

Ive read other posts on different sights where people are saying their mechanical pump is putting out this much or that much pressure, how would they measure it if the pulse from it causes gauge to jump around? Or are they just blowing smoke?

 

[Layne02]

Oh, and I have a liquid filled gauge also that I put on it after this one and it jumped just as bad. So I am pizzled how you check the pressure.

 

[74 Shortbed]

The highest point the gauge bounces to should be your max pressure.

 

[Layne02]

Ok, so, Just to update. I installed a Holley regulator between pump and carb. Put a liquid filled gauge on also. Now it jumps a little between 5-6 most of the time, sometimes it will go between 4-6. So its better, but I was hoping for dead still at 5.5. Anyway, its been an experiment.

 

[Honky Kong jr]

Ok, so, Just to update. I installed a Holley regulator between pump and carb. Put a liquid filled gauge on also. Now it jumps a little between 5-6 most of the time, sometimes it will go between 4-6. So its better, but I was hoping for dead still at 5.5. Anyway, its been an experiment.

With a pulse pump your always gonna get some kind of movement in the needle.

 

[Layne02]

I'm hip

 

[Honky Kong jr]

I'm hip

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[Zoomalot]

One could try what they call an in-line SNUBBER/FILTER in different micron and mini sizes. Made for the PULSE
problems you are experiencing.