RS246.com Forum :: The World's #1 Audi R, S and RS Enthusiast Community

Evening All,

Car has started to run rough, cold start is extremely rough and the revs move up and down a little during the process, once cold start is finished it settles a little but still stumbles and is not smooth

Car lacks any power at all

Whilst trying to log a 3rd gear pull and capture some data the car hit limited itself at 6500rpm

Any ideas?

No fault codes or dash lights at all

Plugs are new and injectors have been out and cleaned recently, coil packs haven't been changed but i would of though i would of had a flashing EPC light if it was a coilpack?

Sounds slightly, similar to what was happening when my high pressure fuel pumps were failing. Though I've not gotten the new ones yet so not sure if it'll be fixed....

Sent from my SM-G991U using Tapatalk

Getsumadis wrote: ↑

Fri Mar 12, 2021 10:17 pm

Sounds slightly, similar to what was happening when my high pressure fuel pumps were failing. Though I've not gotten the new ones yet so not sure if it'll be fixed....

Sent from my SM-G991U using Tapatalk

I logged some data with VCDS the other night with fuel pressure etc both low and high pressure, my low pressure seems to be around 5 bar at idle and my high pressure seemed to actually be higher than specified in quite a few areas in the log, sometimes peaking at 9 bar higher than specified so was wondering if i have a problem with one of the HPFP's

My long term fuel trims are also around -6/7 on both banks so ECU is subtracting fuel

Check the lambda sensors. Sounds a little like the edge of it tripping into limp mode (not sure from the post how great the loss of acceleration is)

Sent from my SM-G973F using Tapatalk

RichT128 wrote: ↑

Sat Mar 13, 2021 12:54 am

Check the lambda sensors. Sounds a little like the edge of it tripping into limp mode (not sure from the post how great the loss of acceleration is)

Sent from my SM-G973F using Tapatalk

Power loss is pretty substantial, only other thing to note was just before I noticed any real power loss and really rough running I could feel a vibration through the accelerator pedal

RichT128 wrote: ↑

Sat Mar 13, 2021 12:54 am

Check the lambda sensors. Sounds a little like the edge of it tripping into limp mode (not sure from the post how great the loss of acceleration is)

Sent from my SM-G973F using Tapatalk

What is the best way to check lambda sensors? I have VCDS

The RS4 has two fuel pumps, and that sounds similar to what happened when one of mine failed. The dips in power seemed to happen at the same point in the rev range, and changing one did the trick - the other is still going strong. There was no warning light.

12th wrote: ↑

Mon Mar 15, 2021 12:43 pm

The RS4 has two fuel pumps, and that sounds similar to what happened when one of mine failed. The dips in power seemed to happen at the same point in the rev range, and changing one did the trick - the other is still going strong. There was no warning light.

The only thing that confuses me is the fuel trims indicate I am running rich as they are negative and my exhaust tips look black again indicating rich running so if I had a fuel delivery issue I would expect to be lean

Fuel trims seem to have returned to just slightly negative on both banks now but car still runs rough and lacks any power, have noticed a fair petrol smell when removing oil filler cap so maybe a hpfp is leaking into the valve cover!

If the throttle is blipped in neutral the revs seem to hang quite badly also and the exhaust note is quiet compared to normal when the car is running well

Have you checked fuel rail pressures? Line 140 on obdeleven not sure if the same on VCDS. Shows requested vs actual pressures

Sent from my SM-G991U using Tapatalk

Heres a link to my thread about my hpfps

https://r.tapatalk.com/shareLink/topic? ... source=app

B7 Rs4 nasty lag/missfire at WOT between 5500/6500rpm

Sent from my SM-G991U using Tapatalk

Yes high pressure and low pressure seem ok although the hp reading does seem to move up and down more than I remember from when the car was running good but the problem is there from the minute the car is started so even present at idle when the hp actual reading is near bang on what the specified reading is

I'm at a loss then. I just got my new hpfps in and installed and that seems to have fixed my problem. Any luck diagnosing yours?

Sent from my SM-G991U using Tapatalk