Dumb Question on fuel pressure testers

[ramba_ral]

Hi all,
I'm in the middle of troubleshooting a fuel pressure issue on one of my vehicles so went out and bought a fuel pressure gauge.( maddox from harbor freight)
I wanted to make sure the gauge was working so I isolated the gauge from the rest of the system to test. I did this by making a hose with a ball valve , pressurized the system , bleed air out and closed the ball valve with no other components in the system.(pump -> ball valve -> gauge) Everything is dry no leaks.

Is it expected for a fuel pressure tester to slowly bleed off pressure by its self?

 

[cgrutt]

Does the fitting connected to gauge have a button on it as shown below?



That is used to (1) bleed air out of system and (2) to release pressure when done.

 

[ramba_ral]

it does yes

 

[cgrutt]

If you press it it should release pressure in hose and gauge (when pump is not running).

 

[Firebrick43]

make sure you put the hose in a gas can before pushing the button

 

[ramba_ral]

yea all that works. I'm saying if i leave the gauge alone it bleeds pressure off with out pressing it.

 

[charbar]

Gauge/tester should hold indefinitely. It's either leaking through the button that cgrutt mentioned or back through your ball valve

 

[Firebrick43]

Pressurize the setup, close the valve, unhook the inlet hose to the valve and put the whole thing in the sink full of water, you will see where your leak is

 

[charbar]

Clamp the line off with something (vice grips etc) between your gauge and ball valve so you can figure out if it's your ball valve or gauge leaking.


How much of a drop are we talking here? How long to drop, say, 10 psi?

 

[ramba_ral]

I tested the ball valve by taking the gauge off and running the pump. Not a drop past the ball valve.
I did spray down the setup with soapy water to find a leak but didn't see any. putting the whole thing in a container of water is a good idea though


it drops about 10 psi in about 2-3 minutes.

 

[charbar]

10 psi in 2-3 minutes should be pretty easy to spot I would think.

Soapy water wouldn't be the best test for that since we aren't looking for bubbles from air escaping. Any leaking fuel would probably blend in with the soapy water and be hard to spot.

If your ball valve is for sure holding Id take that pressure tester back and exchange for a new one.

 

[ramba_ral]

Think I'm gonna take it back and exchange it. I will take the ball valve part and put it in water to see what happens though to make sure its not the ball valve.

 

[jsaw]

If it is not leaking, but the pressure bleeds down, then the check valve in your fuel pump is defective it should hold pressure for a long time.

 

[Firebrick43]

If it is not leaking, but the pressure bleeds down, then the check valve in your fuel pump is defective it should hold pressure for a long time.

he has a ball valve installed, with it closed the regulator isn't part of the system anymore

 

[308guru]

Do your "does it leak" testing with air instead of connecting it to the car. Once you confirm it's good then move on to the car.

 

[joecon]

If you isolated the gauge and the pressure leaked down, there would be gas were the leak was. You may have a leak at the pressure regulator or a fuel injector leaking or the check valve in the tank. Anything else will show as gas leaking out of the gauge or hose or valve.

 

[no704]

Use a lighter

 

[jsaw]

he has a ball valve installed, with it closed the regulator isn't part of the system anymore

That is correct, but the check valve on the fuel pump side can leak so that fuel pressure to drop

 

[rust in the eye]

How long do you expect it to take to read the pressure?
Vehicle fuel pressure checks typically are a go/no-go situation. Need 3 bar and see anything much less and you have your answer.
Not a whole lot of precision needed here

 

[dscheidt]

How long do you expect it to take to read the pressure?
Vehicle fuel pressure checks typically are a go/no-go situation. Need 3 bar and see anything much less and you have your answer.
Not a whole lot of precision needed here

There are things like testing for injector leakage, where you want to see the pressure decay slowly over time (or not at all). If your gauge won't hold pressure, it's hard to know if it's the gauge or something else leaking. Fuel isn't terribly compressible, and the volumes in the lines are small, so it doesn't take much leakage to result in a substantial drop in pressure.

 

[rust in the eye]

Very good point, sir I hadn't thought of that