My dad has a 2002 A6 and we took it down to the beach this past week. On our final day there I started the car, and it sounded like a WRX. Would hardly idle and shaked violently when excelerating. I got to an advanced auto to have the codes run, and it said that the catalytic converter was bad, and misfire on #2 and #6, etc etc.. Bunch of ****.... Prolly explains why it was idling like a STi...lol. So one thing at a time, I want to replace the cats. My question is, if I remove the cats all together, and have a test pipe put in, will this hurt anything? I've been searching on here for a few days now trying to find answers.. I just hate hearing about how much the dealer rips my dad off everytime he takes it there. Any input would be a great help..

Thanks,

John

 

I've just been told my passenger cat converter is bad (bad rattling noise) on my 1999 A6 2.8 with 188K miles. I was considering just yanking them out, but need to understand pros/cons from the smart people here.

Thanks in advance.

 

Whats the other codes? You 'bad cat' code could have been set by the mis-fires.

 

Sorry it took so long to get back with the codes. Maybe some can tell me what they are or what they mean and I can go from there.

p0030
p0300
p0304

Thanks in advance

 

Well, thats only tree codes, and none refer to a bad cat.

P0030 HO2S Heater Control Circuit Bank 1 Sensor 1
P0300 is Multiple or Random Misfires
P0304 is Misfire on Cyl. #4.

First ones fine for now, P0304 is prolly a bad coil.

 

Welcome to the world of the 02 3.0 misfire on cyl 4.

(cylinder 4 is the black sheep of the 3.0)

Mine does the same thing. It may be caused by carbon build up in the head and the ECM freaks on start up. Does it start up rough then run fine?

If so drive the car in S reving the rpm higher on shifting will burn some of it out. Since I have been doing that my misfires went away. The only thing I can do other than that is pull the head and clean it. But this has been working for now. The P0304 is the problem and if any other cylinder misfires just once on start up (normal)it will set off the P0300. To test it you need to do a compression test to see if you have the same problem I do. If you do cylinder 4 will have more compression (200psi) then the others (187psi). Make sure you run Premium gas only!

Keep in mind it could be due to a coil pack they go out at 60K so if they are old you may wish to change them and the plugs. I have read alot about this trying to diag mine and it seems it is always cyl 4 or 3 the two end cylinders on each bank.

To start out swap the orange coil pack and spark plug as long as it is visibly OK with the cylinder next to it and see if the problem moves. If it does by all new coil packs $30 a piece on-line and replace the spark plugs. If it does not move test the compression, You will need to disconnect the injectors from the harness remove the plugs on bank 2 and use a comp tester from any auto store. Install it in the cylinder and crank it over. Take three reading from each on that bank and get the AVG. If your cylinder 4 is higher than the others you have located your problem (too much compression).

Next you need to check the cam lobes for wear, There is a TSB (15-08-03)on the cam lobes prematurely wearing and that will also lead to increased compression (accompanied by an excessive ticking noise) While you are in there check the lifters they should not be worn through. I would suggest buying a Bentley repair manual and a valve cover gasket before you set out to do this.
If you don't have alot of annoying ticking then hold off on this one till later if you do then it is most likely.

It would help to have a VAG-COM that way you can start the car and monitor the firing of each cylinder mine would misfire 20-35 times then run smooth.

If all of that checks out. You may have carbon build up and it is freaking out the ECM on start-up. Mine would take a few seconds to adapt and it will run fine. It may be a glitch in the ECM no way to test that theory without spending $1000 but it it would appear to me that if the compression was the same as the others the problem would go away. I also noticed it gets gradually worse then goes away so I imagine that each morning that it misfires the carbon gets wet and sticky and collects more carbon making it worse until it gets so clogged it heats up and blows out a little. So I dropped that sucker in S and went for a burn. Problem cleared up, for the past 6 weeks anyway.

PM Me if you need more help on it.

Definitely PM me if you cure it.

 

I'd attack the cheapest problem first -- check out the coils and possibly replace the spark plugs as suggested. You didn't mention if the misfire went away after the engine warmed up.

If the suspicion is carbon buildup, then running fuel injector cleaner or Seafoam may help reduce the problem.

My daughter's 2003 A4 3.0l occasionally throws a CEL and Autozone shows a P0431 -- defective catalytic converter followed by misfire, vacuum lak, etc. I have them reset the code and it may be months before it comes back. That makes me think a simple misfire. If it was a bad cat, I would think the code would come back almost immediately.

As far as replacing the cats with a straight pipe, I can't answer. I will tell you that my other daughter's 2002 Vue has had a bad cat for over 100k miles (it's at 165k now) and it never impacted performance or mileage, other than having a "permanent" CEL. Fortunately, she does not live in a state requiring inspection.

 

One daughter gets an A4 and the other gets a Vue? You clearly love one more than the other.