how to test for bad pressure regulator

[eds66bronco]

any tips on testing for a bad fuel rail pressure regulator? i pulled the upper intake last night to pull the injectors for cleaning and want to test the regulator while it's easy to get to. crown vic fuel rails/regulator if it matters. the reason i suspect it is i've only got low 30's on the rail and it drops to mid 20's at about 2000. both fuel pumps are new Carter LP and Airtex hp pumps. regulator holds pressure in the rail for a few hours after shutoff. 4 out of my 8 injectors were not even firing so idon't know if that has anything to do with it.

 

[bluebroncodrive]

are you checking the pressure with the engine turned off?
low pressure is a bad fuel pump, if the regulator is bad the pressure will go up.
the regulator will also hold pressure after the motor is turned off and with the motor running if you pull the vacuum line on the regulator the pressure will also go up it should be good. But I have see one that will stay open all the time (wont hold pressure)

the fuel pressure spec is 35 - 45 psi with the engine not running

 

[Broncobowsher]

With the presures you are stating it sounds more like a bad fuel pump, but could be a regulator.

Quick test, with a couple of vacuum caps on a pair of locking needle nose pliers, pinch off the rubber return line while the engine is running. If the pressure climbs, the regulator is dumping too soon and needs replacement (or adjustment if aftermarket and adjustable). If the pressure doesn’t spike then the fuel pump isn’t up to snuff.

You can also do it by pulling a fuel line, rigging up a new return to a fuel can and starting the engine. Flow out the regulator to the can shows the regulator opening too soon and that is the problem. No flow shows the pump can’t build enough pressure to open the regulator.

Just because parts are new doesn’t mean that they will work right.

 

[eds66bronco]

thanks guys, i'll be giving these suggestions a try as soon as i get my injectors back from getting them cleaned. i can hook up the spare fuel pump and see if that fixes the pressure as well.

 

[Socal Tom]

The pressure is adjusted so that it remains 40 accross the injectors, which means as the pressure drops in the manifold ( vacuum can be as low as 20 inches) so that would cause the pressure to drop to probably somewhere around 20 psi.
Tom

 

[70_Steve]

The pressure is adjusted so that it remains 40 accross the injectors, which means as the pressure drops in the manifold ( vacuum can be as low as 20 inches) so that would cause the pressure to drop to probably somewhere around 20 psi.
Tom

From www.onlineconversion.com ...
1 inch of mercury [0 °C] = 0.4911542 pound/square inch [absolute]

If the 40 psi differential is true, then with 20 inches of mercury manifold vacuum being roughly equal to 10 psi, the rail pressure should be no lower than 30 psi.... I think...

 

[Socal Tom]

From www.onlineconversion.com ...
1 inch of mercury [0 °C] = 0.4911542 pound/square inch [absolute]

If the 40 psi differential is true, then with 20 inches of mercury manifold vacuum being roughly equal to 10 psi, the rail pressure should be no lower than 30 psi.... I think...

man, there is a website for everything! I wasn't sure what the conversion was. Of course were also depending on the accuracy of the guage. I'm not entirely sure what the differential is, but that is how it works.
Tom

 

[eds66bronco]

man, there is a website for everything! I wasn't sure what the conversion was. Of course were also depending on the accuracy of the guage. I'm not entirely sure what the differential is, but that is how it works.
Tom

that is something i hadn't thought about. the guage is one of the cheapo summit racing guages. i'll check it against my father inlaws guage to compare.