Contour Enthusiasts Group Archives Forums Modifications 3.0L Duratec 3L up and running... sort of...

Originally posted by warmonger:

---

Check to make sure your fuel pressure regulator is plugged in and has good vacuum. If unplugged it will run lean under accel.

warmonger

---

It wont make it leaner under accel. Fuel pressure would be HIGHER with no manifold vacuum (WOT conditions) The whole reason the engineers added the vacuum compensation hose to the fuel pressure regulator, is to compensate the fuel injector line pressure with the intake manifold vacuum to make it consistant. Read all about it in this book:

http://www.amazon.com/exec/obidos/tg/detail/-/0837603013/002-2645806-1182436?vi=glance
It goes like this: When manifold vacuum is high (under idle or low load conditions when throttle plate is CLOSED), then there is more vacuum that is HELPING to suck fuel out of the injectors. And when you open the throttle (loading the engine), the manifold vacuum drops, which means that their is less vacuum pulling on the bottom of the spray nozzles, so to get the same injector flow as before (without changing injector pulse width), the fuel line pressure must be INCREASED to compensate for the less vacuum that was in the intake helping suck the gas out. Does this make sense? If you unplug the vacuum line, at idle, the fuel pressure should rise almost or around 10psi from when the line was on. At least, that's what the psi differential was on my old 5.0 Mustang when I had checked it. Each engine's pressure regulator is designed to have the pressure differential compensate the flow perfectly based on all factors (intake vacuum, vs fuel line pressure, vs flow). This is the only way the ECM can have consistent control over what the injectors are spraying under all conditions (without having to make sudden excessive computer calculations (beyond what it would normally need to) in the injector pulse width based on slight changes in intake manifold vacuum. Hopefully this sheds some light on it.