Ford Mustang Forums banner
1 - 7 of 7 Posts

·
Registered
Joined
·
2,471 Posts
Stock pressure is 39 psi. Surging is often because it's too rich, and that fuel pressure would make it run rich. My guess is the gauge is inaccurate if you have a stock regulator. I've run 340lph on stock rails and lines, the pressure was normal. It could also be a defective regulator. Harbor freight sells a cheap fuel pressure gauge you can use to verify pressure. I think most autoparts stores also rent them.
 

·
Registered
Joined
·
2,471 Posts
I'm not trying to start an argument but opening the throttle blade more is going to do nothing but mess things up. The computer controls idle speed. Opening the throttle more will just cause the iac to close more. More important, the computer is calibrated for the amount of air that passes through the the throttle when closed. Moving the throttle blade changes the throttle body air mass and in turn messes up the tune. You should if anything do a base idle reset to get the air mass back to original. That's not going to fix the fuel pressure. I wouldn't trust the gauge without verifing with another gauge. I've had multiple liquid filled gauges be significantly off, including the one that is currently installed on my car now which is the 3rd one i tried. I gave up and just use my aem electronic which i have verified is accurate. Start with what you know is wrong. Pull codes too. How to Manually Test EEC-IV OBD1 Trouble Codes on a Fox-Body Mustang for Free
 

·
Registered
Joined
·
2,471 Posts
Going to check it out see what I can find. What would be best way to make sure the line is clear? Pull it down and blow air through it? Thank you guys for all the input
I would look for a crushed metal return line under the car or a kinked return hose but you may be doing all of that for nothing if the gauge is bad...
 
  • Like
Reactions: kjb302ho

·
Registered
Joined
·
2,471 Posts
I will invest in a new gauge it is pretty old looking.. what are some recommendations? I will let you know if I see anything when I get a chance to jack it up.
I would just look into renting one of the fuel pressure testers, no point replacing it if its accurate. You should be able to rent one from local auto part stores like autozone or orileys. If you cant get one, I would look into getting one from harbor freight or amazon. If you already have a gauge on the rail then you already have the adapter you need to connect a pressure test kit.
 

·
Registered
Joined
·
2,471 Posts
If I’m not finding a damaged return line I will more than likely be dropping the tank to see what pump I have. There’s too much that I just don’t know about the car… the downside of getting someone else’s project lol all I know is what I see
Make sure to check the whole return path. The most common place for kinks is where the return and supply line loop back up near the front passenger side of the engine. Its possible someone kinked the return line back at the tank, or its pinched due to incorrect routing. Its possible the metal lines that run down the front of the passenger side of the motor are damaged but based on the pics, it looks like there are custom lines. Like you said, you never know what someone else did. If you end up dropping the tank to replace the pump, you should be able to get away with a stock 88/95lph pump. Slightly bigger isnt going to hurt but you really dont want to go significantly bigger than you need with a fuel pump. It minimizes heat transfer into the fuel. A 110 lph would be a good choice or even a 150 but you really dont need anything crazy based on your current setup. If you plan on adding a good amount of power to it soon, a 190 would probably be more than enough unless you plan on making a lot of power (450+)
 
  • Like
Reactions: Zboogy101

·
Registered
Joined
·
2,471 Posts
I would build new aluminim lines to replace those hacked up stock lines and flare the ends to adapt to an fittings so you can use Teflon lines to the tank and to the rail. You can do a flow test to determine the pump size without pulling the tank. You can jumper the fuel pump at the diagnostic port and run the supply into a fuel can for 1 or 2 minute(s), measure the fluid amount and then do some math to get your flow numbers.

Example:
340lph flows ~90 gph which is 1.5 gpm.
255lph flows ~67 gph which is 1.1 gpm
 

·
Registered
Joined
·
2,471 Posts
They aren’t stock lines actually they ran new lines and left the original in place lol but was not the best install I definitely would like to run new ones cleaner.
You could go back to the stock lines for ease. They are good up to about 500hp. There are adapters to connect the stock lines and rails using an fittings if you're missing the connections. I have the metal lines that run from the rails down the front of the motor if you're interested in them. If not, new aluminim lines would be the easiest and cheapest way to do it but it's still pretty expensive to do.
 
1 - 7 of 7 Posts
Top