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<blockquote data-quote="SecondhandSnake" data-source="post: 16413278" data-attributes="member: 116684"><p>'</p><p></p><p>Just as a matter of clarity-</p><p></p><p>When I refer to base pressure or delta pressure, that's the same as "pressure drop across the injectors"- it's the pressure of the rail minus the pressure of the manifold. That is the value that the ECM reports through the datalog from the FRPS. It should stay as a static value all the time, regardless of what manifold pressure is doing. Mine appears to be dropping as time and load go up, which is no Bueno.</p><p></p><p>As far as rail gauge pressure, that is pressure in the rail relative to atmospheric pressure, regardless of manifold pressure. That's what's 40psig with key on, engine off (reference pressure = atmospheric, 0psig), and with the engine on, idling at cold start is around 25psig. If maintaining 40psi base pressure that would mean the engine is pulling -15psi (30inHg vacuum), which is a pretty reasonable value.</p><p></p><p>Now for vacuum source, the FRPS and FPR are both tapped into the same source, which is the lower manifold (post blower) That's the actual value they should be looking for, and also the same port as the boost gauge, and what he FRPS is normally tapped into.</p></blockquote><p></p>
[QUOTE="SecondhandSnake, post: 16413278, member: 116684"] ' Just as a matter of clarity- When I refer to base pressure or delta pressure, that's the same as "pressure drop across the injectors"- it's the pressure of the rail minus the pressure of the manifold. That is the value that the ECM reports through the datalog from the FRPS. It should stay as a static value all the time, regardless of what manifold pressure is doing. Mine appears to be dropping as time and load go up, which is no Bueno. As far as rail gauge pressure, that is pressure in the rail relative to atmospheric pressure, regardless of manifold pressure. That's what's 40psig with key on, engine off (reference pressure = atmospheric, 0psig), and with the engine on, idling at cold start is around 25psig. If maintaining 40psi base pressure that would mean the engine is pulling -15psi (30inHg vacuum), which is a pretty reasonable value. Now for vacuum source, the FRPS and FPR are both tapped into the same source, which is the lower manifold (post blower) That's the actual value they should be looking for, and also the same port as the boost gauge, and what he FRPS is normally tapped into. [/QUOTE]
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