kozlovee

HEllo ! I have an Audi S8 2014 4.0TFSI - 520 Hp , and for some time , my car have issue on start up ... bassicly it won t start until I press the acceleration pedal ... I have changed Both of the High Fuel Pressure Pomps , all 8 injectors , the oil separator ....and still my car won t start up from time to time .. for example in the morning the car strat perfect , and after i will run 20 km and stop , after 10 minutes when i want to start the engine again , it will won t start

Jack88

Was this work performed at the dealer? Do you have a VCDS scan taken with a Rosstech cable? My first thought is a crank position sensor, but there are several possiblities beyond what you have already addressed.

e-racer_2.7T

Aren't you under warranty still? Do you live in a warm climate? Could you be getting vapour lock in your fuel system? You're going to need to diagnose and trend the fuel pressure and see if any other codes are showing up. When I'm lost, I go back to the basics: fuel, air, and spark. In your case, one of these is missing. Fuel seems the most likely.

Mike

kozlovee

All what I have done for the car repairs are on Audi dealer .... the error witch appears is " system fuel to rich " ... after I have changed the injectors the error disappear , but my car still start when it s cold ... after I run 10-20 km in city , my car won t start ... I m
sick of this problem ... this error borders me from
last year till august ... I have changed first , the mecatronic from
The gearbox , still the same , after I have changed all the sparks , after the high pressure fuel pumps , after the oil separator ,and then all 8 injectors ... and my car still won t start on warm ... in the morning my car starts good , but later on , it won t ...

kozlovee

i m
living in Romania ... the temperature is variable , 0-15 Celsius

MP4.2+6.0

As mentioned, a scan would be logical way to assess. But in absence of further info, as Jack mentioned the crank position sensor is a logical area to look at. That sensor is known on D3 to fail, known to sometimes work and sometimes not. When it has issues they are often temperature or driving related. And finally, they may not show on a scan at all because all the other engine components first and foremost rely on knowing where the engine position is, and this one is the master and perhaps without sufficient cross validation from others like the cam sensors. For some D3 owners it shows up on a scan. Others have been left at side of road stuck, or similarly find it only starts after car is parked some period of time.

kozlovee

I understand your point of view . Thanks for your interes ... but my Audi is D4 generation , and the problem is on warm engine , my car start up only if I press the acceleration pedal ...

MP4.2+6.0

Ok, whatever. I own 'em both--D3 and D4. You are in money pit world and dismissing help. Sorry if I can't parse all the words, most of which say no start and basically flaky/erratic running and/or temperature related. And to be clear--and somewhat contradicting other replies as well as yours--when you are dealing with car electronics in motor area, yes indeed the core theory is very similar between the two generations, or many other gas Audis or many Euro gas vehicles for that matter. But yes, absolutely please post to correct board instead of shotgun scatter.

Frankly, it could probably be a V6 or I4 gas with similar set ups conceptually. They are most all electronic pedal, Bosch electronics, FSI, coil on plug ignition. Where the sensors are, how many, turbo vs. not, etc. vary, but not basics of push pedal, turn key; 14:1; starter cranks; fuel pumps pressurize (pumpS plural...); coils fire; what sensors do, etc. Meantime changing Mechatronics (in transmission) made no sense to me offhand/with the limited info here, how ever much that cost. No mention of REAR tank fuel pump either. The rocket science mechanics all seem to get blinded by the cool looking HPFP's (pumps) on the valve covers and forget with FSI there is still a basic electric pump in the gas tank to get the fuel to the HPFP's. Cost for that guess would have been 20% of Mechatronics money pit? Or, no runs at electronic gas pedal nor electronic throttle either, both way more logical than even touching transmission. Linking them all, poor info on a full scan beyond a fleeting reference to a dealer (who I would hope could do it, or actually did?). For an issue like this, we too are wasting our time--and yours--if you don't have that information--a current scan as of now, not from before the various rounds of work.

Do yourself and your wallet a really big favor and get a full scan with results in your hands, and/or the tool itself. $200 US.

kozlovee

Hello ! On Monday I will ask for more information , everything I have changed at my car since makes me problems , I have changed on a Audi dealer . I will also tell them to look at the low pressure fuel pump in the tank ... I have 2 months since my car is in their service ...

A 8

You should pay attention to what MP4.2+6.0 are saying, I don't know anyone on here who knows these cars better.

If you are having trouble parsing his words then do this:
-Get the vcds/rosstech tool and do your own scan, post here if you want more help or change the cam sensor and then get the tool if still a problem or for any future issues.