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Old 10-20-2012, 10:54 AM
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bluebee bluebee is offline
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Mein Auto: 02 BMW 525i M54 auto 130K
The information in this thread today belongs here to keep the discussion together:

Originally Posted by ztom View Post
The vac hose effect is to reduce rail pressure at idle, by increasing bypass fuel flow. The cases where hose is tied to the cvv may have an additional effect to increase the rail pressure at high rpm.
Originally Posted by rdl View Post
I've never been able to understand the physics behind the blow for bubbles test. And I never got bubbling: not with 9 inches vacuum, not after my CCV failed entirely (but then it wouldn't with a hole in the drain hose) and not after CCV replacement with vacuum in spec.

Consider that with the vent hose disconnected from the valve cover and blowing into it, the chamber in the CCV is at atmospheric pressure or slightly above; certainly no vacuum. Therefore the CCV's diaphram and orifice will be wide open, ready to draw vacuum on the vent hose (and thus crankcase, if connected) as soon as the engine is started and inlet manifold vacuum is present. The air being blown into the vent hose will take the easy route to the inlet manifold rather than the path down into the sump to make bubbles. It seems to me that the only way to get bubbling would be for the diaphram to be failed closed or the distribution piece on the manifold to be clogged. In this case one would have +ve pressure with the engine running - a definite CCV failure. Yet a pass for a good CCV is supposed to be a little resistance and bubbling when blowing into the vent hose.
Originally Posted by rdl View Post
I checked TIS and the M52 engine does adjust fuel pressure depending inlet manifold vacuum. The M54 engine does not; it uses constant fuel pressure.

However, based on pictures and diagrams I've seen, the connection point on the CCV should be at crankcase vacuum, which is a constant 10 to 15 millibar vacuum. Essentially atmospheric; nothing like the 700 to 900 millibar inlet manifold vacuum seen during idle or over-run. So I can't explain the connection and response by the fuel pressure regulator
Please read the suggested threads and add value, either by pictures or by descriptions, so the next person stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need
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