Modded Mustang Forums banner

1 - 11 of 11 Posts

·
Registered
Joined
·
4,406 Posts
Fuel pressure should be around 40 driving around.
 

·
Registered
Joined
·
2,936 Posts
+1, if you read it at the fuel rail, or the generic PID through the OBD2 port, with a scanner, it will be 40 psi + the intake manifold pressure (vacuum = negative pressure).
 

·
Premium Member
Joined
·
4,464 Posts
+1, if you read it at the fuel rail, or the generic PID through the OBD2 port, with a scanner, it will be 40 psi + the intake manifold pressure (vacuum = negative pressure).
Nope. What you said is only for the rail pressure. The data off the frps should read 40 all the time because its pressure referenced.
 

·
Registered
Joined
·
2,936 Posts
You are correct, that's what you get for relying on 62 year-old memory...

The raw return value for generic PID 010Ah is rail pressure in psig (gauge pressure), which has to have 14,7 psi added to it to get the pressure drop across the injectors.

I was recalling that the raw value was less than the drop, forgot about why...
 

·
US Air Force (retired)
Joined
·
13,542 Posts
Yep. And the result is that my aftermarket fuel pressure gage swings from 30-50 psi as I open and close the throttle. But if you datalog the fuel pressure it says its a constant 40 psi. You can actually test the aftermarket gage by turning on the ignition but not starting the car. My gage will swing up to 43 and then settle at 40 psi (zero vacuum and zero boost).

P.S. The aftermarket gage will also show an increase in fuel pressure when the weather is hot. This is to prevent vapor locking the fuel rails. My aftermarket gage has read as high as 50 psi at idle.
 

·
Premium Member
Joined
·
4,464 Posts
1 - 11 of 11 Posts
Top