E39 530i Struggling to Start

[De@nO]

Got an issue with my E39 530i where it struggles to start when the car has been sitting for a while. say 2 to 3 hours.

it takes about 3-5 long swings before it eventually starts and when it does there is a slight miss for a few seconds before it idles normally. if I turn the motor off and back on again it starts normally as if there wasnt an issue.

Not getting any error codes 
it seems to be a fuel preassure issue, but I'm pretty stumped as I've replaced the fuel filter, fuel pump and level sensor and there are no leaks from the injectors.

Could it be a vaccum leak?

 

[AdiS]

Maybe cam position sensor or crank position sensor? These can cause extended crank cycles before the engine starts


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[Peter@AEW]

Fuel pressure regulator likely.

It allows the fuel to drain back and you need a longer crank period to get fuel in the filter and into the rail.

Also the fact that it will start immediately if switched off and cranked again verifies the pressure hypothesis.

The fuel pressure regulator attaches to the filter with a big spring clip

 

[De@nO]

Thanks Adis and Peter,

The fuel filter I replaced had the regulator built-in.
A fuel pressure test revealed a drop from 5bar to 3bar over an hour so I think its definitely a pressure issue and the issue is, in my mind, as you described Peter.

Still stumped on where its losing pressure as the pump and filter with built-in regulator have been replaced with new oem parts without any change.

Pulling my hair out on this one.

 

[Kyle]

I had the same issue with my E46 320i and the fuel filter fixed it, but that's obviously not your issue...

How's the battery health? 

Also, could you try cycling the key from the off to ignition on a few times before starting to see if that makes a difference?

 

[Peter@AEW]

https://www.realoem.com/bmw/enUS/showparts?id=DT52-EUR-12-2000-E39-BMW-530i&diagId=13_0918

Item No 10 is the vacuum line which is a combination of a hard line with rubber hose ends.

Check the rubber hose ends for pin holes or fraying.
If the system does not hold vacuum it will loose pressure.

 

[De@nO]

Started her up this morning and she started with no issues, the fuel pump was replaced yesterday so I suspect I may have been slightly impatient and perhaps the pressure had to build up over a few drives and stop / starts.

Battery is brand new and vacuum lines are still good. Will see how it goes over the next few days.

Thanks guys!