I'm going to try to keep this as short as possible so you guys will read it all and try to help diagnose my problem, but I've been dealing with the same problem for over a year, so bear with me...
A year ago I brought my 2002 Audi A6 in for a "soft" ticking sound coming from the front end (only during acceleration). I noticed it would tick (almost sounds like a piston misfiring or blown) only when accelerating "under load" and not when rev'ing in park. No lights/codes at the time. The dealership took it for a test drive, and found nothing...
A couple months later the sound was louder, check engine light came on (flashing), and the car bogged out and died while getting onto the highway. I had it towed to the dealership. They said that the engine code said "pistons 2 + 5 (or whatever...two of the pistons) were misfiring." And another code saying the "main computer" was bad. They said they couldn't replace the computer because it was expensive and once they reset the code it did not duplicate. It would have to re-code and happen again to justify a warranty repair. They checked the pistons and engine and said everything else was working fine....
A few months later the check engine light came back on (constant), and the noise was also louder. The code was a "bad catalytic conv." They warranty replaced it and sent me on my way.
A couple weeks later, check engine light came back on....this time the code was also for the "catalytic conv." They replaced it again and sent me on my way.
A month later I needed an oil change, so I asked them to spend some real time road testing the noise this time, because it is ridiculously loud. The problem is the engine seems to accelerate fine, as powerful as it always has been...so the noise doesn't equal reduced performance. It just devalues the car if I try to sell it (which I am), but when people test drive it, they freak because the ticking noise is so loud now. They apparently called Audi's "special" service department to phone diagnose possibilities. I got the car back with new oil, but still the same old noise. They said that because the car is perfoming like it should (except for the 3 cats, and occasional engine light ....) that they could not diagnose WHERE the noise is actually coming from. They said that it could be from anywhere in the engine system, and that they couldn't justify spending the man hours and money to "fish" around.
Two weeks ago the engine light came back on again! I'm bringing it back in this week, and assuming that its probably another catalytic conv. or computer error. I've done a little online research but don't know much about cars. What I've found so far are 3 possible problems (which if any seem likely? and if so, how do I get the dealership to actually fix the problem?):
1) Exhaust manifold is bad - I guess this could cause the noise? Although would it be related to all the other engine codes?
2) Blown pistons - This would cause the ticking noise, but wouldn't it also reduce the power to the point that I would notice?
3) Main computer is bad - This could cause the pistons to misfire, and it could cause the Oxygen system (ESG) to mix wrong which could keep frying the catalytic converters. This seems like the most likely cause, but unless I can prove the with multiple diagnostic codes, they wont replace it.
The warranty covers me until 100,000 miles. When the noise was first reported to them, I had 50,000. At this point I'm up to 87,000, and I'm starting to feel that they are just trying to avoid repairs because it is something major, and the warranty is running out soon. Help! What do I do???
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