Lumpy starting on Mk V GTI

[shazbat15]

Just joined this forum and seen RustyGTI's post about lumpy starting on GTI. Identical problem on ours! Car is 4yrs old, 25k miles, FVWSH, major service 4wks ago, no fault codes stored, diagnostic ( via laptop by VW master tech in our garage showed 4.88 Bar pressure prior to cold start, techie said should be holding about 9 Bar, suspected non-return valve, this starting problem appeared about 3mths ago. It's been at dealer for 2wks they reckoned it was fuel filter/ non-return valve after extensive diagnostic ( 6hrs in total !! ) This part has been changed, got car back two days ago deliberately left it for 24hrs before starting it.....EXACTLY THE SAME !!!!!!.....Can't believe it!.............Anybody any ideas ???

shazbat15......

[bacillus]

Did they check the condition of your plugs?

[shazbat15]

Replaced with new at service 4 weeks ago, battery also checked, perfectly ok.

Any other thoughts?

[bacillus]

Replaced with new at service 4 weeks ago, battery also checked, perfectly ok.

Are you sure they replaced the plugs as iirc VW schedule is @60k?

Not sure why the tech should say your lpfp should be holding 9 bar as the fuel filter has a bypass release valve set at 6.6 bar.

That being said, I would check your pcv as it could have a leak.

[shazbat15]

Thanks for that, just checked invoice, spark plugs definitely changed (our car NOT on long life servicing schedule due to low mileage) would this be reason why plugs changed not because of 25k miles but 4 years old?  The following printed on invoice for starting problem "fuel pressure in limits checked software level of engine - ok, carried out fuel pressure test to fuel system using VAS6550 tester, test fuel pressure from high pressure pump, ok. Check holding pressure in fuel line, found holding pressure dropping under specified pressure of 3Bar.  Testing holding pressure at fuel filter and fuel pump in tank, found holding pressure dropping at fuel filter. Fuel filter return valve faulty.  Requires fuel filter. Replaced fuel filter, tested fuel pressure - ok" .........This doesn't make sense to me because the car is absolutely no different despite them mucking about with it.   You mention possible fault with PCV, will take this up with Dealer first thing Tuesday and let you know outcome.  Any other thoughts on the above, whats the MasterTech talking about when he says 3Bar, I don't understand but your views much appreciated. 

[shazbat15]

Update.

After a weekend of lumpy starting, armed and ready to tackle the dealer, the car started smooth as silk this morning, just like it always used to. Don't know whether I'm more concerned it now seems to be alright than I was when it appeared to be all wrong! Been to the dealer, spoken to the service manager,  he shares the same view! Going to see what happens over the next few days and take it from there.
I know that direct injection fuel systems are pressurised set-ups and I'm wondering if this has all kind of 'balanced out' and settled down? I know that sounds somewhat crazy but is it possible, anybody have any thoughts on this?

[GrayMK5GTI]

Have you read here? -

http://www.mk5golfgti.co.uk/forum/index.php/topic,498.0.html

[shazbat15]

Thanks for this link, made really interesting reading, we initially thought battery could be the problem, dealer said at service 19th March this year it was fine.   Food for thought mind you,  that the incorrect initial battery fitted at production (mine March 08 registered) was never an official recall.  Do you have any further details of  why it was the wrong battery?  eg: was it a lower AHr rated battery than should have been fitted? Any info out there would be greatly appreciated.