Any advice for RS4 B8 with intermittent starting issues

[ABS2788]

My B8 RS4 has started to sometimes not start both cold and when warm. Will crank, sometimes after applying throttle it’ll start then stall and shut off.

Sounds like starving of fuel - along them lines.

Few specialists have looked at it and not sure - no faults showing etc.

Has had injectors refurbed, carbon clean, spark plugs since this issue but still no joy.

Someone said could be hpfp on way.

Anyone any thoughts

 

[spartacus68]

Could be HPFP, however it could be oxygen sensors, etc. With these sort of things you need live data. That means VCDS, and access to technical information, fuel pressure, injector flow rates, etc. Looking at the fuel pump pressure at prime, start and running.

When injectors were refurbished, flow rate tested, new o ring and copper seals, and clamp bolts? Clamp bolts are one time use.

When it was at specialists what was tested, and any conclusions? Mileage?

 

[ABS2788]

From some basic live readings, it said my long term fuel trims on bank 1 & 2 were negative 27%-29%

According to ChatGPT - it could be:

Negative trims can be associated with things such as:

• Injectors delivering/leaking too much fuel
• Fuel pressure/regulation problems
• EVAP/purge valve allowing fuel vapour into the engine
• MAF measurement issues
• Front oxygen/lambda sensor issues
• Fuel mixture/adaptation left over from an earlier problem

The recent diagnostics indicated could be high pressure fuel pumps but the car started each time they had it and no fault codes again.

Since ive then had it back it’s been doing it quite frequently but not every time.

 

[spartacus68]

You can potentially rule out injectors if they were flow-tested, which I assume would have happened during refurbishment - check your paperwork. The injectors are coded to the car, so they need to go back exactly as they've come out.

Has the oil been dropped recently? if you have a faulty injector, you might have fuel in the oil. Any petrol smell over and above the engine oil, or has oil level increased?

There's a certain amount you can do yourself with VCDS. It's only £200 or so for 3 VIN Ross-tech licence and you can run on an old laptop. Check-out Gendan.com

Live data is critical to identifying this type of fault. Useful link here - this relates to an RS6, but worth a read.

Attention to all people who are having hard start issues when car is warm - RS246.com Forum :: The World's #1 Audi R, S and RS Enthusiast Community

On the RS4 B8 - there are two HPFPs from my understanding. I don't think there's coding involved, although replacing both won't be cheap. You can cross-reference part numbers on LLL parts.

Battery healthy too? These cars are susceptible to battery voltage drop. New AGM battery should last 5-6 years and needs coded to car.

 

[ABS2788]

Yes, the mechanic sent them for refurbed and identified injector 1 had a slight leak and 4&5 on its way. Also replaced with main dealer seals

They did a carbon clean and replaced spark plugs and cam magnets as well

I’ve been quoted £1,400 inc labour for two new hpfp but hopefully just waiting for warranty company to approve

Oil is at 3/4 but I’ve ordered some millers ee so will change along with filter soon.

Battery is reading as it should as well

 

[ABS2788]

After some logging, ive got the below -

According to AI, it indicates maybe crankshaft sensor and N80 purge valve.

I am getting very poor fuel economy as well which would be indicated by the short term fuel banks at -25%