Originally posted by Josch:
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




Originally posted by Josch:
It wont make it leaner under accel. Fuel pressure would be HIGHER with no manifold vacuum (WOT conditions)




Wrong. Intuitively you are right, but in actuality you are dead wrong. On our cars with OBDV, the pcm trims the fuel according to idle and load conditions and then uses these figures to calculate the amount of fuel to deliver at WOT. If his pressure regulator were unplugged he would be running 10psi higher as you already stated, but the pcm compensates for this by adjusting the pulse-width to the injectors...very quickly I might add. It would be all great until he went WOT then the computer would expect the fuel pressure to increase...only there wouldn't be any increase since it was already running 10psi higher.
And for further proof, assuming you believe me, I have tried it and tested it with an OBD scanner.

Originally posted by Josch:


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:

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.




Hey, all of this sounds great and thanks for showing us a good book to read.

warmonger

Former owner of '99 CSVT - Silver #222/2760 356/334 wHP/TQ at 10psi on pump gas! See My Mods '05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red '06 Mazda5 Touring, 5spd,MTX, Black