Fox Fuel Pressure Spec Help

Tim Hughes

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Apr 7, 2016
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Hey Everyone, new member here. I have a 93 5.0 with an AFPR, I just checked my pressure and it was at 60 with vacuum off and plugged. Now I know why exhaust burned my eyes while running! So I adjusted it down to 39 but when I reinstall the vacuum hose the pressure doesn't drop like everyone else says it should? Is this normal on a AFPR or is something else going on? Any suggestions?
 
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jrichker

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Lets make sure we have the correct basic procedure first...

Check fuel pressure:
The local auto parts store may rent or loan a fuel pressure test gauge if you don't have one.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line; leave the fuel pressure regulator end of the vacuum line disconnected. Then cap or plug the open end of the vacuum line and stow it out of the way.
Connect the fuel pressure test gauge to the Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure: you should see 37-41 PSI at idle.
Turn the ignition off; reconnect the vacuum line to the fuel pressure regulator. Then disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.



Fuel pressure doesn't drop when the vacuum line is connected - check for presence of vacuum at the end of the line or tubing that connects to the fuel pressure regulator. Stick you finger over the end of the tubing and you should feel suction. Or even better, use a vacuum gauge to check for vacuum. It should read the same on the tubing or hose that connects to the fuel pressure regulator as it does when you connect it to the vacuum tree fitting on the firewall. if it is greatly different, then there is a problem with the fuel pump vacuum line or the port it is connected to. If the are the same or close to the same then your AFPR isn't working correctly.
 

Tim Hughes

New Member
Apr 7, 2016
2
0
1
52
Lets make sure we have the correct basic procedure first...

Check fuel pressure:
The local auto parts store may rent or loan a fuel pressure test gauge if you don't have one.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line; leave the fuel pressure regulator end of the vacuum line disconnected. Then cap or plug the open end of the vacuum line and stow it out of the way.
Connect the fuel pressure test gauge to the Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure: you should see 37-41 PSI at idle.
Turn the ignition off; reconnect the vacuum line to the fuel pressure regulator. Then disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.



Fuel pressure doesn't drop when the vacuum line is connected - check for presence of vacuum at the end of the line or tubing that connects to the fuel pressure regulator. Stick you finger over the end of the tubing and you should feel suction. Or even better, use a vacuum gauge to check for vacuum. It should read the same on the tubing or hose that connects to the fuel pressure regulator as it does when you connect it to the vacuum tree fitting on the firewall. if it is greatly different, then there is a problem with the fuel pump vacuum line or the port it is connected to. If the are the same or close to the same then your AFPR isn't working correctly.
Thank you for your reply, I think maybe you misunderstood my actual question. My AFPR does not drop when vacuum is hooked back up, it stays at a constant 39. I just read on other posts people stating theirs dropped to 30 when vacuum was hooked back up. I do have adequate vacuum, 18hg. So according to your post my AFPR is working correctly! Sorry for the confusion.
 
Last edited:

jrichker

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Thank you for your reply, I think maybe you misunderstood my actual question. My AFPR does not drop when vacuum is hooked back up, it stays at a constant 39. I just read on other posts people stating theirs dropped to 30 when vacuum was hooked back up. I do have adequate vacuum, 18hg. So according to your post my AFPR is working correctly! Sorry for the confusion.

You missed something in the translation...I said it was supposed to drop and then advised you to make sure that there was vacuum on the line that connects to the fuel pressure regulator.

Fuel pressure doesn't drop when the vacuum line is connected - check for presence of vacuum at the end of the line or tubing that connects to the fuel pressure regulator. Stick you finger over the end of the tubing and you should feel suction. Or even better, use a vacuum gauge to check for vacuum. It should read the same on the tubing or hose that connects to the fuel pressure regulator as it does when you connect it to the vacuum tree fitting on the firewall. if it is greatly different, then there is a problem with the fuel pump vacuum line or the port it is connected to. If the are the same or close to the same then your AFPR isn't working correctly.