• Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-

Fox Fuel Pressure Spec Help

  • Thread starter Thread starter Tim Hughes
  • Start date Start date Apr 7, 2016
  • Tags Tags
    5.0 foxbody lx gt
T

Tim Hughes

New Member
Apr 7, 2016
2
0
1
Apr 7, 2016
#1
  • Apr 7, 2016
  • #1
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?
 

jrichker

StangNet's favorite TOOL
In Remembrance. Thank you for your contributions
Mar 10, 2000
27,512
2,813
234
Dublin GA
Apr 7, 2016
#2
  • Apr 7, 2016
  • #2
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.
 
T

Tim Hughes

New Member
Apr 7, 2016
2
0
1
Apr 7, 2016
#3
  • Apr 7, 2016
  • #3
jrichker said:
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.
Click to expand...

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: Apr 7, 2016

jrichker

StangNet's favorite TOOL
In Remembrance. Thank you for your contributions
Mar 10, 2000
27,512
2,813
234
Dublin GA
Apr 7, 2016
#4
  • Apr 7, 2016
  • #4
Tim Hughes said:
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.
Click to expand...


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.

jrichker said:
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.
Click to expand...
 
You must log in or register to reply here.

Similar threads

Fox Fuel Pump Issues After Replacement/Upgrade
  • Ryu
  • Jun 23, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • 2
Replies
23
Views
464
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Sunday at 11:45 PM
Ryu
S
Progress Thread 1989 LX 5.0 convertible - mild project
  • Scott_S
  • Aug 18, 2025
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • 4 5 6
Replies
107
Views
3K
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Jun 26, 2026
AeroCoupe
H
Engine 1987 5.0 HO vacuum hose locations
  • harryhaber
  • Jun 20, 2025
  • Fox 5.0 Mustang Tech
Replies
2
Views
487
Fox 5.0 Mustang Tech Jun 21, 2025
limp
S
Help! Fuel pump not turning on.
  • Steezin636
  • Dec 13, 2024
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • 2
Replies
35
Views
2K
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Jan 3, 2025
Mcmahst
B
'03 GT Fuel Pump/Pressure/Delivery Issue
  • Brodach
  • Oct 21, 2025
  • SN95 4.6L Mustang Tech
Replies
8
Views
869
SN95 4.6L Mustang Tech Oct 31, 2025
gkomo
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Menu
Log in

Register

  • Forums
  • What's new
  • Media
  • Resources
  • Contact
  • Sponsor
X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?

X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?