Gsrob

So, after purchasing my 02 2.7t back in November (with the MIL off), I thought all was well. However, after about a week of driving it, the CEL came on. Naturally, it induced a significant amount of anxiety and I went straight to an auto part store to have the car scanned. I left there knowing that something could be wrong with either the driver side cat itself or one of the o2 sensors.

After further research and lots of help from people here, I decided it was most likely the downstream driver side o2 causing the CEL. At this point, the car ran normally but the light really bothered me. Fast forward to about two weeks ago. I finally got around to installing a new rear o2 on the driver side but the CEL came back on immediately, with the same codes plus a generic circuit malfunction code for the o2 (which previously had only been the heater circuit). Furthermore, after about a day of driving, I got a significant amount of random misfires and a bank 1 lean code. This provoked an even higher amount of anxiety and I began checking everything possible and reading everything possible to figure out what the cause may have been.

I've gotta admit, random misfire codes can throw a person for a loop since there is nothing to identify the problem. After continually scanning my car each day multiple times after short drives and coming up with no further codes except for the random misfire, bank 1 too lean and the rear o2 code, I decided to change spark plugs. The car ran smoother overall, but the misfire was still there intermittently. Next, I tried to clean the MAF. It seemed to improve engine function as well, but the same problem came back after 20 miles or so. To make a long story short (which I've clearly failed at, at this point), I rescanned for codes two days ago and got lucky that a new code popped. Now, I normally wouldn't be happy to have an additional code, but this one allowed me to source the problem. This time, a code popped for the passenger side o2 pre cat. I quickly ordered an NGK/NTK o2 with OEM connector and the misfire went away and the car drives great. Furthermore, today, I replaced the driver side post cat o2 once again and routed it up to the driver side firewall with little trouble. Unfortunately, the Bosch sensor that I ordered had an OEM connector, but not one that fit the brown female connector in the car. The good news was that the sensor came with a new female connector that needed to be swapped over in the box. This process took almost an hour because it was such a pain in the *** to take the old leads of the old, brittle plug. I can't explain how much I wanted to just solder all the leads together and call it a day. In the end though, I got everything out of the old plug and into the new one without killing anyone or breaking anything.

Finally, my CEL is OFF and all is well!!!

BeOhBe

Good to hear it, brother! Enjoy it while it lasts!

You plan on chipping yours at some point?

Gsrob

I hope to get a conservative stage 1 tune at some point. But I'm not real big on ordering a standard program from one of the online vendors. I've always had my cars dyno tuned in the past and I'm hesitant to order something meant for "all cars" that fit into a certain category.

Regardless, I have a heck of a lot more maintenance items to take care of before I can even think about setting money aside for that... V/C Gaskets, Seals, Timing Belt, Control Arms... Just to name a few.

How's your car running now?

georgeb944

Thanks for your post. It got me to thinking about a similar (random misfires on random cylinders), and, after replacing all the ignition coils and both the icms, I was starting to lean towards the fuel pump. Your post had me look at the b1s1 ixygen sensor, replaced it and (fingers crossed), no more misfires.

Sometimes it's just a matter of experience...

(and, oh, yes, I have several 2.7t C5 cars, so swapping parts around is not as expensive as it might sound.) ,,,

Gsrob

Good to hear! If you don't mind me asking, how'd you come across all the 2.7s? Did you find people looking to part their cars out?

georgeb944

No, they are all runners, bought my first (2001) in 2004 from a friend of a friend. Tiptronic with a problem with locking torque converter, it currently has 270K miles. Second was a 2008 ebay purchase, another 2001 A6, this time with a 6MT, now has 190K miles. Third was last year, a 2000 6MT with 140K miles, bought from an Audiworld ad.

I find them to be fairly reliable, and, if you do your own work and diagnoses, cheap to own.

Gsrob

That last line there is the truth. I saved a ton of money on diagnostics. I'm sure that if I would've taken it to a shop (which I never would have regardless of how dire the problem) that they would've tried to sell me on every common ignition part possible, even though all of them are completely fine. Like you, I was lucky enough to find a 6 speed as well. From everything I read, you save yourself a lot of headache since it's so much more beefy than the tips. Currently mine has 145k on it and all original o2 sensors with Audi logos prior to my replacements.