Fuel Pressure Check (Hard Start)

WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 1999 BMW Z3, 1999 BMW M3, 1999 BMW M Roadster, 1999 BMW M Coupe, and 1999 BMW 740iL. However, it is still accessible from the selected car via links, so may be relevant.

Run engine at idle then turn off. Note fuel pressure. Note fuel pressure again after 20-30 minutes. If fuel pressure decreases by greater than 7.2 psi (.5 kg/cm² ), turn engine on, wait for pressure to stabilize, then turn engine off and immediately clamp off intake line near pressure gauge with Clamp (133010). Note fuel pressure. Read fuel pressure again after 20-30 minutes.
If fuel pressure drops by less than 7.2 psi (.5 kg/cm² ), check for fault in fuel supply lines, in-tank supply hose, or defective non-return valve in fuel pump. If fuel pressure again drops by more than 7.2 psi (.5 kg/cm^cm2 ), replace pressure regulator.