Audi A6 2002, bought used in 2005.

Got a blinking check engine light + vibrating engine without power while on highway last year. Slowed down the car, problem disappeared. Brought car to dealership and they replaced cat converter. They told me it was hard to diagnose the problem, but that this should do the job.

The car was running much better, but still felt a little bit underpowered.

This year, on a long roadtrip, the problem came back. However, this time it happened in the mountains. Using the tiptronic, shifting down, I got through the vibrations and the mountains, but then engine stopped running - burning smell. Had the car towed. Codes showed tons of missfires.

The mechanic said that it was most likely the ignition coils. Replaced 6 coils, but check engine light kept blinking like crazy and the ride was rough. Codes: missfiring. Mechanic told me to get the ECM reflashed at dealership. This helped, but now the check engine light is blinking when I am driving on the highway, going from 40 to 55 mph. Again, the engine feels low on power and the car starts to vibrate. Codes indicate missfires and a problem with the cat converter, which was replaced last year.

Since all coils were replaced (had the spark plugs replaced at the same time), the ECM was reflashed and there is a pretty new cat converter, what could be the REAL problem? Could there be a problem with the fuel injectors?

 

Well apparently you didn't read your owners manual because misfires and flashing CEL's means DONT DRIVE THE CAR GENIUS!! You probably just fried both of your brand new cats. Have the car diagnosed by a dealer technician, it will probably be the ICM's (ignition control modules)

 

Point well taken, but how do the fried cats explain the erratic behavior of the car? It runs smoothly all the time, although it seems a bit underpowered, but the engine vibrates only between 40 and 55 and the check engine light blinks for a few seconds. If I increase speed slowly though, I can get through this stage without problems.

I can see that running the car while missfiring creates gunk that the catalyst converter does not like. But how does this affect the performance of the car?

 

At 40 - 55, the torque converter locks, allowing you to feel previously masked mis-fires. The performance of the car (or lack there-of) is affecting the cats, not the other way around, until, of course, the cats are fried. Then, either the engine can't get rid of its exhaust or the ECM sees excess oxygen in the post-cat sensor and starts dumping in fuel to "cure" this perceived problem.

Good luck,

Bob

 

Bob martain pretty much covered it, a lack of power will be caused by the misfiring engine and the cats are now plugged so it affects the exhaust flow. Not to mention if its missing really bad you could be damaging your pistons which is a mucho expensive repair if you keep driving it.

 

Thanks for the input, this all starts to make more sense.

But when the cat converter was replaced last year by the dealership, the problem did not seem to be solved. I spent more than $700 on the replacement, but the car was still underpowered, though the check engine light did not light up.

I then had the CEL come on during the road trip through the mountains, and it seems to me that the cat converter could not have initiated this problem. So, the problem then must have been the ignition coils, correct? I then replaced those, got the computer reflashed, but I still have problems. If I understand you guys correctly, this issue is caused by a bad cat converter, which was the result of running the car with a blinking CEL and bad coils. Which makes sense.

However, how do I know that the problem is finally solved, when I replace the cat converter? Why was the cat converter replaced in the first place? Mileage was only ~55k, I never ran the car with a blinking CEL, the coils seemed to be fine back then. What could be the cause of the missfires? I guess I am repeating myself - apologies - but any input is welcome before I spend another $700 without solving this problem.

 

NO.. you had a bad cat because of the mis-fires.

Misfires are coils, wires, plugs, ecm, cam sensor, crank senser, temp sensor, throttle position sensor, fuel pressure, fuel pressure regulator, injectors, leaking intake, carbon buildup, etc, etc, etc.....

you need to take it to someone who actually knows the car...

 

Midniteoyl, we are on the same page (perhaps not well explained in my last post), I am looking for the thing that keeps the engine to misfire. Unfortunately, I think the dealer is not. They replaced the cat converter last year, without solving the original problem.

 

True.. most dealerships will run the codes, check the obvious, look at the TSB's and Recalls... then give up, replace the parts damaged from the problem they cant find, charge you and wait for you to come back.

I had a car that wouldn't start on the first thru third tries, and ran with a slight ping afterwards. Took it in and got killed on a pressure regulator replacement. No go. Took it back and got killed on a fuel pump and filter. 2 days later, same problem. Took it back only to be told they couldn't reproduce the problem (what?? after three times they tell me now??) and sent it home. After calling the service manger and getting the run around, I called the owner. 20 mins later I was called and told to drop the car off and get a rental. 2 days goes by and I called and told its ready. The problem? Chaffed fuel pump wires. This was the original problem and it caused a low pressure in the rails leading to all the parts replacement (and $$).


Moral? Just because they are 'certified' doesnt make them smart. 2 simple checks at the pump would have caught the original problem (pressure then voltage).

 

^^^That i can vouch for 10 fold. I know a lot of dumb *** audi techs....