difficult starting after standing for several days

[johnaboy183]

I have noticed of late that if my car ( 2.0TDI 170) stands for more than few days it takes numerous cranking attempts to start. Once started its fine and starts first time every time. I am figuring diesel drain back on standing and thought I once read there was a non return valve in the fuel line that could cause the problem. Can anyone shed any light on this for me please?

[johnaboy183]

Once again no replies unfortunately! This forum used to be a hive of activity and help but now (looking at the variouos recent posts) almost no replies are received by anyone - but yet hundreds of reads.
Has all the "expertise" disappeared or am I missing something?
Surely someone must be able to point me to where the non return valve or tee pice that does the same is as I know many others have suffered similar problems with diesel drain back?
John

[Roy_01]

There is a pressure retention valve in the return line from the injectors.
This should keep the pressure at 10 bar when the car is shut off.
Or maybe you have a bad injector that is leaking.
Other options: bad battery/battery drain

[johnaboy183]

Thanks for the reply. Would the retention valve you mention cause the diesel to drain back to the tank?
The primary pump seems to work fine as even if it has stood for days the pump after a few repeated attempted starts gets the fuel back up and the car starts and runs fine after that. The battery is brand new and works fine ( thank goodness as otherwise the repeted turn overs would have flattened my old battery).
Where is this retention valve - is it visible under the bonnet?
John

[Roy_01]

Hi, yes it's in the main line that return fuel back to the fuel filter. Must be somewhere around the engine.
What you can do is prime the fuel system a couple times with vcds when the car has been standing still some days and see if it makes a difference.

https://workshop-manuals.com/volkswagen ... el_system/

https://a.allegroimg.com/s1024/0c36ef/7 ... d0c33f6bb0

[johnaboy183]

Thanks for that info. I didn't find such a diagram in the Scirocco Workshop manual but will look again. Now that I know what I am looking for I will have a better look under the bonnet. I found the attached item on Google under Scirocco pressure control valve but not sure if it is the same item as it does not appear like the one you have shown. I had thought of trying the priming option in VCDS but as the engine runs faultlessly once it starts or is restarted within a day I wasn't sure if priming would help - seems to me more like a possible leak leading to a drain back or a tiny leak in a one way valve or O ring but will keep looking!

[johnaboy183]

On further thinking I feel the attachment I posted is probably just part of the N75 turbo "Moo" valve but maybe not!
Also is there a direct two direction path between the high pressure side of the fuel system and the low pressure side as if not then could this pressure retention valve allow the low pressure line to drain back to the tank do you think? (hope that is understandable)

[Roy_01]

Yes it's in the workshop manual page 225. It's just above the valve cover on the right. Looks like a rubber grommet.
The valve in your picture is the high pressure fuel rail pressure regulator. This could also be leaking yes but i think your car will run horrible if it does.
I believe you it runs fine once it starts but you want to pinpoint your problem.
You can run both fuel pumps in engine basic settings channel 035.
Or connect a pressure sensor in the fuel return line from the injectors back to the low pressure fuel system so you can see what it does after a couple days.
Can’t discover a pressure retention valve in the fuel line going back to the fuel tank.

https://www.dropbox.com/sh/nerw5cwkh9ug ... EA189).pdf

[johnaboy183]

Sorry just read this now as have some domestic repairs over the last few days!
The car runs excellently once started and will start first time every time if used daily - the problem only comes when stood for several days.
I think your manual is far newer than mine so thanks for that but I cant see any picture on Page 225 and looking at the drawings on the following pages none seem to show what you describe. Are you sure its page 225?

[Roy_01]

There is a picture on page 219

[johnaboy183]

Time to go play hunt the valve I think! Thanks for the help

[Roy_01]

What pressure does your high fuel rail pressure display when the car is shut down?
I see 8 bar.