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Old 06-22-2013, 02:23 PM
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Bad fuel pressure gauge?

Hey all;
Long story short I installed a Fuel Pressure (liquid filled) gauge and a fuel pressure regulator on my SBC400. I was having hard starts when cold and the gauge was showing about 8-9psi with an Edlebrock. So was using the regulator to cut it down.

The gauge bounces a little when car is running, and always higher at first startup. So I would tune it down, and after some on/off cycles with the car, the pressure would show around 2-3psi. I took her for a drive the first time and she drove pretty good, little hesitant off the line but solid. I look at the gauge while motor is still running and it shows 0psi. Obviously not 0 since the car wouldn't be running, so is it a bad gauge?

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/D

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Old 06-22-2013, 03:34 PM
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Yah, I'm curious for a response as well, my summit liquid filled guage was showing 11psi when cold, so this morn I turned it to 5ish, when its hot it reads 1-2 psi and seems to now have a lean surge on the highway.
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Old 06-23-2013, 12:16 PM
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The problem with the liquid filled gauges is that the "reference pressure" is that small air space within the gauge. As the liquid heats up that pressure increases and this is affecting the gauge reading. A non-liquid gauge references to the air outside the gauge. All quality liquid-filled gauges carry this disclaimer.
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Old 06-23-2013, 01:46 PM
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Quote:
Originally Posted by toddalin View Post
The problem with the liquid filled gauges is that the "reference pressure" is that small air space within the gauge. As the liquid heats up that pressure increases and this is affecting the gauge reading. A non-liquid gauge references to the air outside the gauge. All quality liquid-filled gauges carry this disclaimer.
Which was my understanding, accept mines backwards to that.
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Old 06-23-2013, 03:49 PM
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Quote:
Originally Posted by bygddy View Post
Which was my understanding, accept mines backwards to that.
Why do you think it is backwards? The gauge is looking at the differential between the air space and the actual fuel pressure.

If the fuel pressure is 7# (above atmospheric pressure) and the air space has a pressure of 4# (above atmospheric pressure) because the liquid is heated up and exerting pressure on it, the gauge would read the 3# differential.
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Old 06-23-2013, 07:23 PM
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So after app 5 min run time, the needle read 2psi, I adjusted it up to 6, and let it run, it stayed at 6. Then hours later restarted it, it now read 9 for again, the first 3-4 min, then dropped down to 6 and remained there. So I'm going to leave it alone.
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Old 06-24-2013, 08:40 AM
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So then what would be the solution to fix the gauge? Empty out the fluid? I got this installed so I could see what's going on, and right now it's useless if it's going to be doing that.
I was under the assumption that the liquid filled gauges were best for underhood references.
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Old 06-24-2013, 01:09 PM
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Originally Posted by david-b View Post
So then what would be the solution to fix the gauge? Empty out the fluid? I got this installed so I could see what's going on, and right now it's useless if it's going to be doing that.
I was under the assumption that the liquid filled gauges were best for underhood references.
The non liquid filled guages bounce bad from fuel cavitation when using a mechanical pump.
I would try what i ended up doing, and that just give it a few min to stabalize, then set it and see if it changes. Mine was all over the board, and still shows 9psi on first start, after a few min it drops to 5.5 and stay there consistant.
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Old 07-10-2013, 12:56 AM
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i guess i got lucky... I used a quality industrial pressure gauge from Ashcroft. (not liquid filled) never had a problem with it bouncing..

i installed the pressure gauge on the regulator.. still no bouncing.. in fact... I believe I have a you tube video of it.. hang on a sec I'll look ~

]intermission music here[

yep. .here it is.. sorry for the awful audio.. but the mic in that camera SUCKED

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