fuel pressure question

[jfoj]

Originally Posted by upallnight

If the fuel pressure is not vacuum controlled then why is the fuel pressure regulator attach to the intake boot with a vacuum line? Incoming air through the intake boot does create a vacuum (pressure differential) when it passes over the small opening of the vacuum line connector. This is bernouili principle of fluid dynamic.

If you find and read the BMW documentation on the M54 you will see they clearly do not have vacuum controlled fuel pressure on M54, this is by design and is DIFFERENT then previous engines.

As for your Bernouili principle, just disconnect the FPR hose at the connection on the intake boot, install a vacuum gauge, check the "vacuum" at idle, there WILL NOT be any. Then go out and beat the vehicle into the ground and come back and tell me how many inches of vacuum you were able to measure/observe.

You will find there is no appreciable vacuum at this point. If the air filter is dirty beyond where anyone would typically operate a vehicle you MAY see 1-2 inches of vacuum at WOT, but none at idle!! Fuel pressure that is vacuum controlled has MAX vacuum at idle or decel and little to no vacuum at WOT if it is sourced from the intake manifold and not a venturi port in the throttle body. This is directly opposite of how a vacuum controlled fuel pressure system would operate.