B6 A4 3.0 catalytic converter replacement

[hurleyint1386]

Hey everyone. Wondering of anyone had an experience with replacing the catalytic converters on a 3.0l B6 A4. Having a friend do it and hes got the driver side cat taken care of, but there's a bolt that he can't get to. Wondering if anyone has any idea how to get to it. It's the top bolt on the cat, it's on the other side of an O2 sensor. It's a very tight squeeze and can't get in there to get it out. He's tried through the top and bottom, but no go. This is the only thing keeping him from getting everything finished. Any tips or tricks would be greatly appreciated. Thanks

[Kenrussell3]

I'm having the same issue...one bolt on top of the cat. I'm new. I'm trying not to post something already answered previously, BUT has anyone ever answered this post?

[2004a4b630QT]

The top bolt needs to be removed via the engine bay. Remove the intake and cam position sensors on the left, and the sensors and coolant tank on the right. It's a bit hard to get to. ELSA repair database says to remove both o2 sensors from the top too. If it's an automatic, they recommend removing and moving the trans cooler lines and prop shaft connection in the front.

[SJorge3442]

For those top bolts, you're gonna fight them all the way out. I'd recommend using a pass through socket and/or short extension. I believe they are 13mm (friend should know this), but the pass through sockets make a big difference and are great for reach in small spaces. On the drivers side, get the cam sensors+coolant tank out of the way and on the passenger side, you need to remove the SAI piping, otherwise it is gonna suck even more than it already does.

Why are you replacing the cats? JW, as the rear o2 sensors are the reason why most change cats, although its almost always a sensor issue, not a cat issue.

[Kenrussell3]

I was getting a P0421 code for bank one, so I put a spacer on the passenger side downstream 02 sensor. It gave me the same code. I did not put a spacer on the driver side.

[Kenrussell3]

I got the driver side cat and down pipe unbolted, and I removed the 02 sensors. Now there doesn't seem to be enough room to remove the cat and pipe out of the car.

[Kenrussell3]

I'm going to sound a little stupid here, but what does it mean to "remove and move the...prop shaft connection in the front", and how would I do that?

[DarkoNova]

I believe prop shaft is what non-north American countries call the driveshaft. So I'd wager you're supposed to disconnect the driveshaft from the tranny and move it out of the way.

It should only be 6 bolts.

[ralleyquattro]

Yes, removing the driveshaft and driveshaft shield gives you TON of room to do anything you need from the bottom, replaced front O2 that way in less than 1/2h.
Well worth the 6 bolts on driveshaft, one stretch bolt on the outer CV and the 3 bolts holding the shield.
Oh yeah, not to forget the 5 holding the wheel, removing that will also help you to remove the driveshaft.

[2004a4b630QT]

I don't see any mention of lowering the subframe so I'm just mentioning it in case. The cats won't pass through otherwise.

[Kenrussell3]

Thanks for all the input. I'll get back under the car and let you know how it turns out.

[deyrag]

Just be careful that you don't screw up the flex section of the piping or you will be back in there again.

[Spike00513]

I believe prop shaft is what non-north American countries call the driveshaft. So I'd wager you're supposed to disconnect the driveshaft from the tranny and move it out of the way.

It should only be 6 bolts.

It might just be how they refer to the various shafts.
A long center prop-shaft in the middle, and then small short half-shafts (CV axles) on the sides, going to the wheels. Short for 'propeller shaft'

[DarkoNova]

Just be careful that you don't screw up the flex section of the piping or you will be back in there again.

Yeah I'm pretty sure that's the source of the weird noise my car makes now. I pulled the engine to do the clutch and left the cats attached to the manifold. The pipes got bent pretty good, but I've read they're only supposed to be bent around 10-15° at most.

Now the exhaust makes a rattling kind of noise every now and then. :(

[Kenrussell3]

Ok. I'm back. Looks like removing the CV shafts would have given me a lot more room, but it is not going to give me the 1/2" more clearance I need to remove the cats from below. I am not yet comfortable with dropping the sub-frame. I have never done that before. I will look for instructions. I finally figured out how to actually get a socket and ratchet to remove the 13mm nuts from the two lower cat bolts from below and removed them. I was then faced with the seemingly impossible task of accessing and removing the nuts from the top cat bolts. I was able to figure out the "angle of the dangle" and got a 13mm socket and short wobbly extension and long handled ratchet on the top nuts, but was only able to remove the drivers side. The passenger side appears to be "frozen", even with a pipe cheater bar over the end of the ratchet. I applied WD40 and another anti-rust spray with no luck. I can't see a way to get a torch in there. I'm going to see if I can get some extensions and try to use my impact wrench from below.

[2004a4b630QT]

Ok. I'm back. Looks like removing the CV shafts would have given me a lot more room, but it is not going to give me the 1/2" more clearance I need to remove the cats from below. I am not yet comfortable with dropping the sub-frame. I have never done that before. I will look for instructions. I finally figured out how to actually get a socket and ratchet to remove the 13mm nuts from the two lower cat bolts from below and removed them. I was then faced with the seemingly impossible task of accessing and removing the nuts from the top cat bolts. I was able to figure out the "angle of the dangle" and got a 13mm socket and short wobbly extension and long handled ratchet on the top nuts, but was only able to remove the drivers side. The passenger side appears to be "frozen", even with a pipe cheater bar over the end of the ratchet. I applied WD40 and another anti-rust spray with no luck. I can't see a way to get a torch in there. I'm going to see if I can get some extensions and try to use my impact wrench from below.

Good work getting those nuts. You're in the home stretch. Get some pb blaster or liquid wrench if you can and soak the nut for hours if not overnight. As for the cats, so far as I know there's only 2 ways to get them out. Through the engine bay after the heads are removed or out the back of the subframe. No way around this. Be glad you don't have a tiptronic. Many more steps to get around that beast.

[SJorge3442]

FWIW, I was able to get my drivers side DP out without touching the subframe, but I did remove the axle iirc

Sent from my LG-H871 using Tapatalk

[Kenrussell3]

Well....still under the car. After spraying anti-rust and waiting over night I was able to get the top cat bolt off from the passenger side. Then I slowly removed the rear sub-frame bolts (3 on each side), still not enough room to remove the cats and down pipes. Then I removed all but one front sub-frame bolt on each side, then slowly loosened the remaining bolt slowly as far as I could, safely, without removing them completely, thus holding the sub-frame from dropping completely. That gave me enough room to remove the driver side cat and down pipe, but still not enough room to remove the passenger side. I lacked about 1/2". I tried every angle, and twisted and shoved to no avail. Finally, I found the correct tool. Using a piece of 3/4" heavy duty pipe and a sledge hammer, I was able to "tap" the cat back through the opening between the fender and transmission. Wahoo!!
Now I am putting everything back together. The new cats and down pipes were a tight fit from below, but manageable. The top manifold stud on the passenger side came out with the "frozen" nut, so I replaced it. Just a note...its easier to install the O2 sensors after inserting the new cats and down pipes into the area between the fender and engine, but before connecting the cats to the manifolds. The best tool I found to loosen and tighten the cat/manifold nuts was a 13mm swivel-head ratchet wrench (GEAR WRENCH or Harbor Freight equivalent) and long arms from below. Ok, now I just need to put everything back together. I'm replacing the inner CV boots, while I'm at it ($16 special order from Autozone). Only one other problem...I now have a coolant leak from somewhere at the back of the engine. Maybe a heater hose came loose, when I lowered the engine?

[EuroxS4]

Top bolt you can get from the top,but your gonna need a short rachet make sure its on there all the way then use a extension or piece of pipe on top of the end of the handle for the rachet hit it with a hammer should break free.Thats the best full proof way to do it.Just make sure the socket is all the way on.Otherwise youll be making alot more work for yourself.

[Kenrussell3]

Well...it is now October. I finally got everything put back together. The coolant leak mysteriously disappeared when I raised the subframe back into place. I then had an exhaust leak where the new down pipes connected to the tail pipes, due to the crimped ends on the new downpipes. The OEM pipes are full round (not crimped) so that they fit into the OEM coupling sleeves that connect the down pipes with the tail pipes. To make everything work with the OEM sleeves, I had to cut two short pieces of full round exhaust pipe and slide them over the crimped ends of the new downpipes, then slide the coupling sleeve in place, then tighten the clamp bolts. Or, I could have lengthened the tail pipes by adding a piece of full round pipe to make them long enough to slide over the crimped end of the new down pipes and then using the two clamps provided with the new cats and down pipes.
Once I got everything buttoned up, I had to erase the catalytic converter codes and go through the notorious "drive cycle". I found the trick to the drive cycle. Drive 5 minutes on the highway at a constant 55-57mph from a start, then repeat. That will get you through the catalytic converter drive cycle. The rest will follow with normal stop and go town driving. In Arizona you can go through emissions testing with one system not ready. I watched carefully and immediately drove to the testing station, when only one system (secondary air) was left. It passed. Yay! When the secondary air system finally went through the drive cycle, it threw a code, but it was after I passed emissions. So I finally got this Nevada car titled and registered. Now I have two years to figure out the final code. By the way, the car has always run perfectly all this time. The passenger side cat was clogged, the driver side looked fine. I just decided to replace both at the same time. I took a chance with the O2 sensors. They are working fine.