residual "high pressure" in GDI systems.

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residual "high pressure" in GDI systems.

Postby expl0de » Tue Aug 23, 2016 12:10 pm

Hello to the comunity,
The only place in the network to find some information about what the rail pressure should be after engine off, was this site - In the article about high pressure sensor testing in common rail diesels.
My car is BMW petrol direct injеction and Im trying to diagnose intermittent long cranking.
I have stable 5 bar low and 150bar high pressure at idle and under load high pressure goes to 200 and low stays at 5, which is within the specs.
After I turn off the engine, the low pressure goes slightly up to 5,4 and the high pressure starts to drop(reverse flow through the HPFP i guess, but is it normal?) For 30 secs it drops from 150 to 100 bar and continues until it equalls the low pressure, then both fall to about 4 bar.
I am going to remove and test my injectors for leaks and spray pattern , but I wonder if it's normal this high pressure drop after engine off.
expl0de
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Re: residual "high pressure" in GDI systems.

Postby STC » Wed Aug 24, 2016 3:52 pm

I would put the fuel pressure drop and removing the injectors on the back burner for now.

I will have a look at the specific strategy for that control unit later today but it would not be normal or safe to hold any pressure, let alone 100 bar fuel in the pipework with the vehicle switched off.

I think I would be looking at Fuel Pressure, Crank Sensor, Injectors and Primaries, MAF, MAP, EGR, Starter Current ..... through the eyes of the scope. All of which need to captured during the "Long Cranking" Being intermittent that may be difficult to achieve but it has to be done.

Second best may be data logging with a capable scan tool permanently plugged in to capture it.

I certainly wouldn't be pulling the injectors out, or anything else just yet.
STC
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