Elias C Dib

Hello All,

I am hoping to get some help with the issue I have with my 2001 A6 2.8L Quattro 95K miles. First, let me say, I love this car. <--- "be careful what you ask for brotha!" I truly do tho, it drives great until now.

The vehicle had a steady check engine light related to O2 sensors and fuel banks. The vehicle does 18 mpg combined city/highway per rating for this vehicle, so I ignored fixing them, given I live in the state of Michigan, no emissions inspection or inspection required.

I recently had a gas leak from a nipple part of the gas tank, luckily was covered by an Audi recall back in 08 -- Fixed it for free ($3000.00 worth).
As a result, the dealer broke the already rusted through muffler/resonator pipe. Quoted $6000.00 for parts and labor to change catalytic and resonator, they were all shot, I said goodbye.

I purchased an aftermarket catalytic kit PA/DR sides, with 4 new O2 sensors, a resonator and had them installed today at Mr. Muffler on Woodward Ave and Royal Oak in Michigan - great guys 5-star shop.
Catalytic converter kit --->https://www.ebay.com/itm/322452691706
Resonator ---> https://www.ebay.com/itm/191678963849

I also had a misfire on cylinder 4, so I installed new spark plugs (P/N: IK20TT#4 4702 IRIDIUM TT spark plugs --> DENSO supplier), and a new ignition wire set (P/N671-6165 also DENSO supplier); the engine runs smooth and the misfire went away from #4.

After I received the vehicle today, I realized a very suttle engine vibration when in IDLE and on D. Also on R. The check engine light flashed then went away completely. I thought the ECU took some time to recognize the new O2 sensors, shook hands, and became friends. But after I got on the high way, cruising using cruise control at 2800 RPM, the car would slightly stutter every 2-4 minutes (like very slightly) then the light would flash again. Now the engine light goes on steadily until it stutters again (very gentle stutter) then the light would flash again immediately after the stutter.

From what I read on the forums, I could be dumping fuel into my new cats and eventually could fry them dead.

Does anyone here have experience dealing with a similar issue? What should I check for?
Could it be possible that one of the spark plug wires is loose?
Could it be the new O2 sensor?
Could it be the vacuum system causing this?

At the end of the day, it feels like a misfire.

Thank you all for your support.

Harleyguy

You need to pull malfunction codes. Most any parts store will do that for free. Option 2 is to find someone that has VAG COM scan tool for more accuracy. Auto Zone and others can probably pull up basic fault codes. Google the code numbers to get specific info.

Elias C Dib

Thank you Harleyguy,

I will go to an Autozone today, and will search for the VAG COM on Monday.

Quick note here, I took the car for a test run on the high way again this morning:

The behavior triggering engine check light to flash is as follows;

- I step on gas; the engine lags for one or two seconds, then the RPM revs up then normal from there. This happens at any given RMP.

- This performance behavior also occurs when cruising steadily. I set the cruise control at 3100 RPM about 85MPH and monitored the dash (thankfully the highways are semi-empty today), every 15 to 30 seconds, the engine would slightly lose some power then rev back up, enough that it is noticeable.

IMPORTANT NOTE: This behavior did not occur before I changed out the exhaust pipe and O2 sensors. The spark plugs and wires were replaced prior to the exhaust and O2 sensors, and the misfire at #4 went away, smooth sailing again.

My assumption is this:

- One of the spark plug wire-plug is lose, but this would cause a misfire in idle anyway.

- The ignition coil is malfunctioning, need a new one installed.

- The new O2 sensors are messing up the system, or the O2 sensors were installed incorrectly i.e. not to their proper connector (Pre/Aft Catalytic).

I will post the results of the scan once I receive it.

Harleyguy

A good independent repair shop will have a VAG Com system scanner. Most of the DIY'ers on here recommend Ross Tech. You purchase an interface cable then they give you data base access. Probably the most accurate as well as most reliable. Cost is around $300 but only works on older Windows Operating Systems. Last I heard, nothing for Mac. My guess is that either the new O2 sensors were installed wrong, bad connection, wrong sensor(s). A scan will tell you the answer. When a problem jumps up after a repair it is certainly something that occurred while making the repair or the repair itself. I didn't look at your link but did the Cat kit include the O2 sensors? Some of the after market sellers out there are selling cheap Chinese parts that look like OEM parts but are unusually lower priced than factory. This is usually a red flag. The result is often poor fitment, shoddy finishing, non-function and so forth. When looking for parts shop several online sellers. This will give you an idea of what the price should be. Then if you find that item somewhere for only 5 or10 per cent of the going rate, buyer beware. Some of the better suppliers are ECS Tuning, Autohaus AZ, Blau Parts, and many more.

meternerd

The new VCDS works just fine on my 64 bit laptop using Win 10. You choose either 32 bit or 64 bit version when installing it. Just got it a couple of weeks ago from Ross-Tech. USB interface.

Elias C Dib

So it could be that the O2 sensors are bad quality, but:
Does it matter in what sequence the O2 sensors are installed?

My fear is that the mechanic plugged the fore/aft catalytic sensor connectors backwards.

I called the mechanic Ill be heading there, but I rather be an educated consumer, than be clueless. Thank you.

georgeb944

You need a VCDS scan. All your questions will be answered by the scan, or at least you will have a clue.

Asking the questions without having done the scan is a waste of time.

Elias C Dib

I visited this issue at the mechanic today after doing a ton of research. E46fanatics forum had mentioned that if the O2 sensor connectors were swapped, bank 1 with bank 2 or fore/aft the vehicle would run lean or basically, like a washing machine.

See this link ——> What symptoms to expect with o2 sensors are installed backwards? - E46Fanatics

The mechanic confirmed bank 1 and 2 O2 connectors were swapped, installed them correctly, and cleared codes.
The car run smooth again, and I can finally enjoy the value of this $1500.00 fix

Thank you all, I’ll bring in codes (first) next time.

Harleyguy

Wah Hoo glad to hear. It is a good thing your mechanic stood behind his work. Unfortunately many do not. Audis can be difficult to sort out even with the experienced mechanics. You don't necessarily want someone working on it that "thinks" they know what they are doing. These are too expensive to throw parts at and take guesses as to the problem.

AudiNike12

$1500?! Glad that's not me. But great that everything is fine now