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Matt
Matt, Mechanical Engineer
Category: Audi
Satisfied Customers: 22175
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have audi 2009 A6 3.0 TFSI supercharge 290bhp CAJA engine.

Resolved Question:

hi. I have audi 2009 A6 3.0 TFSI supercharge 290bhp CAJA engine. My problem is with cold start long cranking (around 3sec before start).
It only happens when car is not in use for several hours (park over night), otherwise it
start on the touch of a key.
No error massages on Vagcom.
Any suggestion?
Submitted: 15 days ago.
Category: Audi
Expert:  Matt replied 13 days ago.

Hello

This sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.
1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,
Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

You can also get this issue with contaminated fuel , if there’s water or dirt in the tank then either the petrol floats on top of the water or the filter sock on the pump is choked up – so if the other things check out then I’d consider pulling out the fuel pump and cleaning the filter sock

And one other thing to try is to loosen off the fuel filler cap, as there’s a 1 way valve built into the cap to let air into the tank and so prevent a vacuum from being created as the fuel leaves the tank to the engine
If this helps then replace the cap with a new item

Expert:  Matt replied 11 days ago.

Hi
do you still need help?
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Customer: replied 10 days ago.
hi. My apology for delay. Im very busy at the moment. I will cam back to you by the end of the week.
Thanks
Slav
Expert:  Matt replied 10 days ago.

understood

Customer: replied 8 days ago.
Hi.
First thanks for replay.
I checked all fuel system (components) and all is ok and working as it should.
The only difference what i found is pressure readings in group 140 3rd block on VCDS (see pic).
Cold start 0.99 - 1.3 bar compare to 45 bar on any other time.
Im not sure where the readings coming from as I don't have description to the group or single block.
Please let me know what you thing.
Thanks
Expert:  Matt replied 8 days ago.

hello

OK the group 140 block refers to the fuel pressure after the high pressure pump

so the middle block of 55 bar is the specified pressure and the 3rd block of 45 block is the actual pressure

so its showing the high pressure fuel is lower than it should be so you may have a faulty Gdi pump or a blocked fuel filter

this blog post should be useful

http://www.ross-tech.com/vag-com/m_blocks/

Customer: replied 8 days ago.
Is the specified pressure fix value for all time when engine is running or it very?
Did the high pressure pump should hold pressure till next start or will will release after some time?
Injectors can leak is well. Is there any way to find what is leaking pump or injectors?
Fuel filter been changed 15k ago (I thing need to be change every 40k). I will do it again.
Expert:  Matt replied 8 days ago.

Hello

the specified pressure will vary with engine speed and load

at full power it should be at 200Bar for example

I'd agree changin ghte filter as the next step as its a cheap part

if that does 't boost the pressure then either you have a leaking injector or a faulty pump

you can check for a leaking injector by leaving the car a few hours after a drive and then pulling all the spark plugs to see if any are wet

if you do have signs of fuel in 1 cylinder then either replace that injector or try some fuel cleaner into the tank

Matt and other Audi Specialists are ready to help you
Customer: replied 6 days ago.
I will do filter first, and try to look for any injector leaks checking spark plugs and with endo camera.
Im little bit sceptic about fuel cleaners, but I may try some.
I may come back if I stack with something if you don't mind in the later date.
In the meantime thanks a lot for your help