When I was testing the fuel system for leaks with ISTA on my X3, the procedure calls for fuel pressure buildup at the rail while the car is off. So I would say "yes" to your question. Pressure needs to be present in the rail even when the vehicle is not running but only for some time. This explains the noise the car makes when you first wake it up in the morning.
try the ISTA fuel system leak test.
Quote:
Originally Posted by woo102
So I took a little break from this car, but I'm not done with it yet.
I checked for big gaping holes in the air intake path but couldn't fine any.
I spoke to someone who used to work on bmws and he was wondering if the O2 sensor started going bad and causing the mixture to richen over time.
I pulled the DME fuses to erase any fuel adaptations. I disconnected the O2 sensors, put a new set of plugs in (thank you FCP Euro), and started it up.
With the O2 sensors unplugged, it idled fine.
I let it idle for a few minutes.....everything was great.
I did a fuel pressure leak down check: with the vehicle idling and good fuel pressure (about 10 MPa), I shut the engine off with the stop button. I turned the ignition back on (without starting the car) and saw the high pressure fuel rail pressure was down at 0.61 MPa (about 80-90 psi) I believe this is not good. I think the fuel rail pressure should remain high for some time after shutting the engine off. This may mean I have a leaky injector(s).
......anyway......
Took it for a ride, had ISTA connected and reading the voltage, high pressure fuel rail set point and actual pressure, and the charge pressure. I had my girlfriend video the ISTA readout.
Drive down the street, and it did the same thing that it did on the previous 2 attempts: ran smooth, then start to drop a cylinder(s) and sputter, lose power, then stall.
This all happens in about 1,000-2,000 feet.
After it stalled, I could start it up again, but it would stall every time I put it in gear.
It stayed in neutral after stalling, so I was able to pull it back home with another vehicle.
Anyway, after getting home and reviewing the video, I see that the high pressure fuel rail pressure would drop to from 10 MPa to 0.61 MPa immediately when it stalled.
Can anyone confirm that the fuel rail should retain pressure for some time after shutting off the car?
I'm starting to think maybe I do have injectors going bad (leaky) as was mentioned earlier.
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