bstellar

I traded up from a B7 S4 Avant to my RS4 this spring and have managed to put on 7000 km since delivery. Absolutely love the car and should have saved the money and just gone straight to the RS when i purchased my wagon.

Approximately 3 few weeks ago the car felt like it was slightly down on power, especially in low to mid rpms. Convinced myself that i was just getting used to the car, as i had been using it as more of a daily driver. A few days later on my commute in to work, the MIL light comes on (solid - not flashing) so i naturally log into AW and spend some time searching the forum archives to see if other owners have been experiencing similar issues. Called my local dealer to make an appointment and my service advisor immediately mentions the much discussed TSB's for the fuel pressure sensor and the intake manifold/vacuum pressure issue. Dealer squeezed me in for the following morning (friday) and a few hours later called to say it was ready and they had found random misfires on cylinders 2 and 4 and had replaced 2 coil packs. I've owned more than a few VW/Audi products so i wasn't surprised by this. Picked the car up after work but due to rush hour traffic i didn't really get a chance to open it up to see if the power-band had changed, but it still felt a slightly lacking.

Parked the car for the weekend as i was leaving town and sure enough, Monday morning the engine light came back on during my drive in. Called my service advisor and they graciously made room for me to bring it in that wednesday. Tech calls me at the end of the day and lets me know that they are finding random misfires on all cylinders and asks me about the fuel i use as he's seen issues with FSI engines and non top-tier gas. I only use Shell V-power or Husky 94 premium which never caused issues with either my B7 S4 or my FSI powered Touareg. Tech decides to be sure it's not bad fuel, to drain tank and fill it with a tank of V-power from local station and run the vehicle while hooked up to the diagnostics. Calls again later to tell me that he is still getting random misfires and will need to keep the vehicle for the next day.

The following afternoon my service advisor calls to say the car is ready and they had found a vacuum leak from a main line from the reservoir. This makes me optimistic as i know of the TSB's for this issue and the multitude of systems in the car that rely on vacuum pressure. I pick the car up and the service tech takes the time to open the hood and walk me through the vacuum lines and show me how they are dealing with it. They also installed a check valve in the line from the reservoir tank which they claimed has been effective in similar issues with the R8 engine.

Took the car out for a couple of good highway drives this weekend and it still feels like something isn't right. The top-end power seems okay, but the low to mid range still doesn't have that "stuck to the seat" feeling it once did.

Questions that i hope can be answered:

1. - Is there any chance the service tech has reset the ECU and it needs some more time and miles to remap.

2. - Is there a chance the fuel pressure sensor TSB would apply but is not throwing the error code.

3. - Could the check valve the tech installed be preventing the system from reading an error in another part of the vacuum system that control the intake manifold flaps or valve cam timing adjusters.

My dealer seems determined to rely on the cars computer and Audi's outlined procedure rather than using some logical insights or taking any risks. I'd be more than willing to pay for a new fuel pressure sensor or some additional vacuum lines and labor to get my car back to it's original self. I'd also be interested in having another RS4 owner take it for a drive just in case my butt-dyno is misleading me.

Any help would be very much appreciated.

Thanks,

Brad

Jenner

Reseting the ECU usually increases performance as the reduced timing valves reset.

Based on your description it sounds (to me)like the intake manifold flaps have stuck open in high RPM mode. This would allow your RS4 to make normal power from 5500-8250rpm but below 5500rpm the intake path isn't optimal for performance or economy.

Do you notice a change in g forces around 5500rpm when you are at full throttle? There should be an increase in g around this rpm similar to the kick of VTEC engine.

I had malfunctioning flaps that never caused a CEL/MIL. The EPC light came on and then wen t off after turning the car off and on. My flaps would stick closed(low rpm power) or stick open(high rpm power) or sometimes work. A code was stored in one of my ECUs.

The solution was to replace my intake manifold. If you search you can find my post(s) about this.

The first time I had the EPC light on the dealer did the vacuum line TSB you mentioned, but obviously that didn't fix it.

That's not to say it isn't anything to do with the fuel pressure sensor but since there is already a TSB out for this and it sounds like your dealer is going exactly by the book then perhaps they already checked for it. I too thought I needed the fuel sensor replaced and brought the TSB into the dealer to suggest it. They told me it wasn't it and I was back in a week or two for the intake manifold replacement not for fuel sensor replacement.

bstellar

Thanks Jenner - i appreciate your response.

I did follow your posts regarding the intake manifold and it's on the top of my list of suspects, but i have yet to see the EPC light.

As you described - the engine breathes great from approx. 5k rpm up - which IIRC is where the manifold tumble flaps change modes. I have been trying to gauge the fuel consumption as well, but i haven't been able to get enough mileage in lately to really see a drastic change.

I'm curious if the vacuum line check valve the tech installed would prevent an error code in the intake manifold from being read.

FYI - the tech also noticed my driver side front strut leaking when they switched out to my winter wheels. Looking forward to the DRC fun on top of this

MrBucket

My car needed the fuel pressure sensor and it wasn't giving me any codes

silverRS4

Sensor G336 (Intake Manifold Runner Position Sensor) monitors this. The Audi tech should know this. Do you have access to VAGCOM?

bstellar

Thanks Tim - my new VAG-COM arrived yesterday. Now i just need to find a decommissioned PC at the office to run the software. It would be nice if Ross-Tech would port over a Mac OS version.