View Full Version : EFI Fuel supply & return pressure regulation question
ironman16nc
01-19-2012, 07:44 AM
I have a 4.6L SOHC from a 97 Mustang GT that I'm trying to figure out the fuel lines on. I'm using an in-tank pump with return line. There seems to be two devices in the original lines (see circles in pic). There is a fuel rail pressure regulator and I'm guessing either a check valve or return line pressure regulator to hold back pressure on the rail before returning to the tank? Is that right? I'm thinking of 6AN braided hose to make the connections to the supply/return lines but the return device becomes an issue - do I need it? What do I replace it with (since I can't get the #%$@ thing apart)?
7531
ironman16nc
01-19-2012, 03:44 PM
UPDATE: Doing some more web surfing, I think I found the answer. I believe that the return line on this engine normally has a check valve on it (righ circled item). The story is this maintains pressure on the rails when the engine is off. When you want to start it back up, you quickly have enough pressure on the injectors to start the engine. Without this I would have to cycle the key a few times in order to bump the pump enough to build pressure. Not having this valve might also cause lower fuel pressure at higher RPMs. Of course it's a very hard item to find. I'm checking to see if the new fuel pump I installed has a check valve in it (later model Mustangs did). Bottom line - I need to make sure the rails have pressure on them to get a good engine start. The left regulator makes sure the pressure is correct and the right check valve keeps it there.
ironman16nc
01-19-2012, 08:39 PM
REDIRECTION: So even more web surfing and study of the Chilton book...maybe that's not really the return line, its probably the supply line. Also, I contacted the fuel pump supplier - they have a check valve on the supply port, not the return port (actually makes much more sense). I believe this is the real story: The pump supplies fuel to the supply with the check valve to prevent back flow when the pump stops. The on-rail pressure regulator is at the end of the line and relieves into the return line that runs unimpeeded back to the tank. This puts the correct pressure on the line while running and maintains pressure when the engine is off. Since the new pump has a check valve, the inline valve at the engine is not needed. Hope this might help anyone else trying to work with a 4.6L.
riptide motorsport
01-19-2012, 10:10 PM
I believe your correct in everything yuou have stated here...Steven