Originally posted by warmonger:

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.


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

warmonger




What I had explained to you must have COMPLETELY went over your head because, what you think I was explaining wasn't even what I was trying to say. I know how OBD II works. I went to several workshops on how they work. My employer pays me to go to professional workshops that teach me concepts that come from reputable sources, since I work in the field as a tech. Do you know what pressure differencial is? Do you know what compensate means? All the vacuum diaphram is for on the fuel pressure regulator is to COMPENSATE for the PRESSURE DIFFERENTIAL between intake pressure, and fuel line pressure. This has nothing to do with the ECM's normal metering and trim programs for actual running (idle, part throttle, WOT) conditions, other than to COMPENSATE. Please study what you know before you preach it. And read my post again, but more SLOWLY. I tryed to put it into lamens terms by using easy words like suck, and help and stuff. But even though I say vacuum, scientifically, there is a just a LOWER pressure in the intake manifold than what is in the fuel line, and at various throttle positions, this pressure 'differential' between the two, changes, which affects FUEL FLOW consistancy at any given set pulse width (since the computer has NO idea how much pressure is in the fuel line and cannot compensate for it in OPEN LOOP since it has no MAP sensor). To eliminate this variance in flow from throwing off the engine's normal fuel adjustment program, the automakers had decided to eliminate this simple change in injector flow that was being caused by PRESSURE DIFFERENTIAL, so they made an intake pressure to fuel pressure 'adjuster', if you will, which is built-in to the fuel pressure regulator. This is how it is, I don't make the rules. Why don't you plug in a fuel pressure gauge, AND a vacuum gauge up to your engine and watch the pressure change in fuel line act in a DIRECT relation to intake vacuum, and study it for awhile, and you just might begin to make the corrilation between why the vacuum might affect the fuel pressure in such harmony. And go buy the book too

PS- Sorry if I sound kinda testy, but I'm right in this matter, and I don't want others to be misled by misinformation

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