These figures would be for a stock truck. All bets are off if you require the injection pump to pump more fuel.
Above is the quote where I thought you were implying that mods would adversely affect the LP's ability to provide a minimum 8 psi.
I'm glad my post didn't come across as a flame to you, that was certainly not my intention.
I certainly hope that the quote you took from the DC service manual isn't implying that the pressure should only/can only be read at idle, because we've heard tell on these boards and I've seen with my own eyes that a pressure of anywhere from 7-12 psi can be read at idle
even with a dead LP , because the VP44 will PULL enough fuel for you to get a reading, you'll only see the pressure go to 'heck' when under throttle, indicating that the LP is not providing the pressure you're seeing at idle when the LP is dead.
Maybe what we should be comparing is 'mad mods' of the 350+ HP variety when we're talking about what kind of mods would make the LP unable to maintain the
volume of fuel being required at 8+ psi at the inlet to the VP44, the kind of mods which motivate people to upgrade their fuel lines, banjo bolts, etc. to allow more VOLUME at the same pressure.
I've tried to understand your straw reference and I think I see where you're coming from, that based on the volume demanded the pressure can't keep up? I'm not a fluid dynamics expert by any means, but my example would be to think of a compressor. You'd set the PSI required for a given tool, say 90 psi, the tool requires that PSI be maintained to work. If you have a compressor that's capable of maintaining that pressure, the only variable would be the compressor's ability to maintain the VOLUME of air required to maintain that pressure, no? And at that point, if the compressor doesn't have the volume necessary to maintain the pressure then the available pressure (psi) begins to drop accordingly. Ok, I can see that.
However, we're talking about serious mods that could do that to the stock fuel delivery system. I'll tell you that most of us, myself included, cannot get the pressure to drop below a certain point even with basic mods (for me it's 10 psi with a new lift pump with my EZ), those basic type of mods should not cause a pressure drop at the inlet of the VP44. And most of these basic types of mods are easy enough to disconnect to confirm pressures without the mods to prove either to ourselves or to the dealer that the LP is dead/dying.
I guess what I'm saying is I don't believe that with basic mods that pressures would be/should be reduced when more fuel is required and is being demanded by the VP44 to provide the power being demanded. I'm thinking the pressure (PSI) should remain steady and the only variable is the VOLUME of fuel that the LP is capable of delivering at that PSI, based on the size of the fuel delivery system, i. e. fuel lines, banjo bolts, et al. , and as long as the volume of the fuel delivery system is not overcome by the demand from the VP44 the pressure being provided by the LP at the inlet to the VP44 should remain steady. And, if you've got the kind of mad mods that would cause a volume of fuel to be called for that would render the LP unable to maintain a 'spec' pressure, say 8 psi, you'd at least have a PARTICULAR pressure (say 5-6 psi) that you could not cause to go down under any circumstances, and you'd either know it was your 'mad mods' that was the cause or you could disconnect some or all mods to prove that without said mods you could maintain the factory 8 psi or better.
Hope the above makes sense, sorry for the long post but I, and I'm sure other people, would like to get some of these factors straight in our heads and try not to
cause confusion for some of our newer members. We get enough confusion and doublespeak from the dealers when we go to them to try to get what we perceive as our problems fixed.
zman
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