What is the advantage of using Schrader Valve on fuel rails.

[amirfarzad]

Dears

Is there any body can explain what is the main reson they design and use a Schrader Valve on the returnless fuel rails. As I can imagine there is some advantage with releasing gasoline vapor when the temperature rises and flow is blocked. also if they want to repair an injector for instance they can releas fuel pressure before disassembeling them from fuel rail.The next one is to use Schrader Valve when measuring fuel pressure. if there is any other as well? Also what would be a problem if there is no valve on the fuel rail and what is other alternative solution?

Regards

 

[TStaples]

amirfarzad,

You are correct regarding the primary reasons. A diagnostic port is required so that vehicle service techs can measure pressure, and/or introduce service chemicals into the systems. It is also required to SAFELY bleed down system pressure prior to disassembly and service. It may or may not be used for bleeding air out of a returnless system during initial startup after assembly or re-assembly. (I do this myself when I'm wrenching on my stuff. It saves wear and tear on the starter motor. But I'm not sure if any engine plants are doing this prior to cold/hot testing.

-Tony Staples

http://www.tscombustion.com

 

[Fabrico]

There is no problem except that you can't do any of the things listed. My Grand Cherokee V-8 has no such port in the fuel rail.

 

[TStaples]

Fabrico,

Not sure if yours is the same, but my '99 Grand Cherokee 4.7L had the newer style Siemens fuel rail assembly with the notoriously leaky quick connectors. (I hope someone got fired over that debacle!) The Schrader valve was located on an inlet line, just prior to the rail, and not on the rail itself.



-Tony Staples

http://www.tscombustion.com

 

[aamatureracer]

NHRA and SCCA racing uses the fuel rail tap to sample fuel and I have built fuel sampling systems to retrofit many cars. There are some fuel injected cars that do not have sample ports and more than one have found fuel pumps that are not producing the pressure needed for the injectors to spray properly. This usually results in a high speed miss that is hard to diagnose because it only happens under load.
I have made some to fit street cars especially the injected Jaguars as they seem to have fuel pump issues, something about a Lucas syndrome has been mentioned. Look at the website

http://www.fuelports.com

for more information.
Have a safe and successful race season.