Rs6 c7 warm start problems please help

[S15MPO]

Hi folks wondering if anybody can help at all
I have recently bough what I thought was a gem of a car it’s a 1 owner 58k fash example from a local well established dealers
On paper the car is perfect and really looks a genuine example standard as the day she was born I had been looking for a while for a stock car and this turned up on my door step I was chuffed!!!
She test drove fine and the garage waited for me to sell my bitdi a6 private which I thought was good of them
The car came with 3 months warranty
Of which the first 3 weeks of owning I could not even drive the car for insurance reasons (long boring story) so finally the day came I could use the car I’ve been wanting for years
Then it happened after doing less than 500 miles in the car I noticed after leaving the car for roughly 2 hours parked up at work I went to start the car and it cranked for what felt a life time started very roughly then fell flat on her face…… after several attempts it started and seemed to run fine
The previous night I did notice it started like it was running on 4 cylinders for a split second then cleared up
Since owning it it has always seemed a little rough on idle but out it down to the v8 rumble
The car is now back at the dealers but would love to know your opinions on what it could be please!!…
I read a lot on fuel pumps so I have done and am waiting for the results of a millers oil test to look for fuel dilution
I have had the car plugged in and fuel pressure at the time was 27bar at warm idle
It was not a 1 off when I got home I left her to cool for the same 2 hours went out to start it and again cranking but takes ages to fire then stalls
Other than this the car has been amazing for the short time I have had to enjoy it

The garage are struggling to replicate the fault apparently and are logging the running data to send to “tech team”
But I think this is going to be the start of the end of a very short relationship sadly!!!
Thanks for any help and I will post any findings

Update 19/12/24 the dealers just got back to me with a vague answer that they are replacing only 1 of the hp fuel pumps…… I asked them to explain why they think it’s only 1 at fault and basically they couldn’t but the warranty company will not replace both so that’s where I’m at!! Still no oil test results as yet
Again any help would be much appreciated
Cheers

[S15MPO]

Update:
The garage replaced passenger side HPFP car is now starting on the button every time hot cold or warm it’s made a huge difference
The mechanic said it showed signs of bleeding back into the low pressure side just slightly more than tolerance range
I’ve done the exact same trip left the car for the same length of time for over a week now and it’s not missed a beat
Personally I think they should of replaced both pumps but apparently warranty would only replace 1 so looks like I’ll be replacing the other in near future out of my own pocket but I can’t fault the car ATM…
Big thanks to Pete & Trevor at Dave fox motors!!

Also the oil report has come back looking good with less than 1 percent fuel dilution with good reports on condition from Millers

Bit of a one sided post…..no doubt because I titled it wrong or something but fingers crossed it can help somebody with similar problems

[DrJSL]

Glad you got it sorted! Hopefully just teething issues, now you can unleash the V8.

From my research, these high pressure fuel pumps seem to fail prematurely on quite a few examples. I believe the part is only around 400 each, so hopefully a good indy can do your other one for a good price!

You mentioned the car had FASH - might be worth clarifying if the 40k major service was carried out - including diff oil, spark plugs etc etc.

[Revilo]

Shame they did not replace both, but understandable if they were able to diagnose only one with issues. At that mileage it likely won’t be long until the other needs replacing too.