80 PSI Fuel Pressure "Oh My"

[2trux]

I am working on my sons 90 B2 which is suffering from low gas mileage and high idle (as much as 2500 RPM). I changed the injectors thinking they were leaking. It still sounded like it was not running right. I put on the fuel pressure gauge and it is running 80 PSI. I assume this is too high as my 88 and 89 run between 30-40 PSI.
I assume I need a new pressure regulator. Any other ideas if there might be another cause for the high pressure. Also the pressure doesn't hold, when the key is turned off the pressure drops to 0 in about 10 seconds.

 

[RonD]

Yes, change the FPR(fuel pressure regulator) its stuck closed

Stock fuel pumps are capable of 80+ PSI

Stock FPR is rated as 45psi maximum pressure with no vacuum present, so thats the most you should ever see on a 1997 or earlier Ranger/BII
The vacuum when engine is running lowers it to average 30-35psi range, the vacuum stabilizes the pressure because vacuum goes down when throttle opens, and fuel demand goes up, so it balances out
Without the vacuum the pressure would drop with demand and jump back up with foot off the gas pedal, computer would have a hard time calculating injector open time with larger swings in fuel pressure


Most likely the check valve inside the fuel pump is bad
The 3 things that hold pressure with key off, is the FPR(but its stuck closed), the injectors all being closed, and the check valve inside the fuel pump
Its possible the FPR is also leaking enough to cause the drop, so I would replace that and check pressure again for the drop

Check valve is basically just a flap that is pushed open when pump comes on, flow pushes it open, then when pump is off flap closes because of reverse flow from the 30psi press at the engine
So a drop to 15psi would be OK, but 0 psi means pressure is leaking out somewhere

Not a big issue on the 1997 and earlier, because with key on you should see 10psi come back for start up which is enough to start engine, then pump comes on full time
1998 and up needed 60psi so the 10psi is often not enough to start engine

 

[2trux]

Thanks, I will order one. I need to take it off because the fuel line connector looks very different from my 89 and I want to make sure I get the correct one.