Test fuel pressure with a tire gauge?

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Hi,

my car (1997 Volvo S40) has a nipple connector on the fuel rail to check fuel pressure. That nipple is exactly the same as the one on tires. Since I have a tire pressure gauge on my air compressor, I was wondering whether it would be possible to check the fuel pressure SAFELY with that tire gauge! Actually it is possible bt I'm unsure if that's safe because the connector on the tire pressure gauge is held by a spring and it's not bolted on the nipple on the fuel rail. Therefore I'm unsure if:

1) fuel may leak
2) the fuel pressure would be accurate

Apparently ther's no leak when just setting the ignition on (engine not started) ad I get a fuel pressure reading of about 40psi. But do you know if that's an OK method to check fuel pressure (with engine on) or is tis dangerous/inaccurate?
 
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My concern would be self immolation. One slip and you spray yourself and a possible ignition source, the running engine, with a mix of liquid/vapor gasoline. Buy a fuel pressure gauge with a schraeder valve end. Harbor freight had them for 39.99 and I think OTC has a kit w/several adapters for 89.99. Years ago we had one of our salesmens cars in for repair, a 94 crown vic and the guy testing the fuel pressure connected a gauge to the schraeder valve and made the test. When he took the gauge off and started the car, gas sprayed everywhere. The schreader valve stuck open. No fire, but the gas bubbled the paint under the hood and took the shine off of the clearcoat on the fender.
 
For emergency use to test for high/low pressure, this could work OK. Then throw it away.
But it won't respond correctly to test variations, and I doubt the materials would hold up inside.
 
I never thought of using a tire guage for that. I think that there would be inaccuracies because a tire guage is meant to measure air pressure and not liquid pressure, so maybe you'd get a false reading because there's no place for the air to escape that could get trapped in the gauge. Fuel guages have a bleeder valve that lets you expell all the air, but they also have long lines for air to trap in.

Of course, the gasoline will probably ruin the tire guage. I'm guessing it would probably give you a pretty accurate reading once anyway.
 
Pressure is pressure.

The schraeder valve in the test port is too deep to be depressed by a tire pressure gauge. Have enough shop helpers over the years and this comes up.
 
No pressure is not pressure! Air is highly compressible gasoline is not any where near as compressible as air. Is the pressure of the fuel even in psi? Fuel will leak where water or air would not this is why some radiator shops test with gasoline as the final test not with air pressure or water.Air pressur egages are not designed to have solvents inside of them and for the most part gasoline is full of solvents.Ever put automotive oil in a syringe designed for human use? It swells the rubber inthem so much that you can never reuse it again. What if this air tire pressure guage starts to disolve in his hand. The saftey risks are not worth being a cheap "insert word for rear end where waste comes out of body" in this situation....You might end up like my Father in law! He did something stupid that he had probably done well over 10,000 times in his life time and now he is in a wheel chair because that one time got him!
 
I am not sure how the pencil style tire gauges work and if they would measure anything but air. If it is a tapered tube and depends on the viscosity of the fluid, no. A Burbon tube type gauge, which many dial gauges use, is accurate with any fluid. Even a metal one may have rubber seals gasoline would ruin.
 
Originally Posted By: JohnBrowning
No pressure is not pressure! Air is highly compressible gasoline is not any where near as compressible as air. Is the pressure of the fuel even in psi?


Yes. The pressure of fuel (or any other liquid for that matter) can be specified in PSI, and is specified that way in Ford shop manuals for one. In my Saab manual I believe it's specified in bar, but 1 bar=14.5PSI so you could figure it out from that.
 
I'm not really sure how a tire gauge measures pressure, or if it will measure liquid pressure accurately. I assumed it was spring loaded
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But when I think about it, I tend to agree that pressure is pressure. If a fuel pump will deliver 40 psi of fuel pressure through a line that has some air in it, then it should be able to deliver 40 psi of fuel pressure if the air bleeds out of it too.

So I tend to agree that pressure may not be volume, but pressure is pressure.
 
AutoZone has a fuel pressure tester in loan a tool. its pretty new but deposit only get all your money back when done and has a bunch of adapters etc...
 
Kilou, do you need to check your fuel pressure? if so, do it right. use the proper gauge and be confident you will get the proper result's. are you a good mechanic or a 1/2 assed shade tree, old technology guy. autozone DOES have the proper tool to use.
 
Tire pressure gauges are for checking pressure in tires. Get the right tool, for safety and best results. If not pay someone to test the fuel pressure for you.
 
Originally Posted By: StevieC
Also the Tire Pressure gauge is calibrated for air and not a liquid.


It doesn't matter. Agreed using a tire gauge to check fuel pressure is not a bright thing to do, but pressure is pressure be it liquid or gas (air). A psi or bar is the same no matter the fluid.
 
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