Broken Cat...decisions decisions

This issue was getting mixed in the other thread.

So I’ll start from the beginning…relevant mods: APR stg 2 tune, Neuspeed cat-back exhaust (so downpipes to tips), stock motor mounts, roc euro intake, 100 octane blend, tracking the car at Mid-Ohio. Unfortunately no logging going on.

At turn 10a, the car started to sound like a 65 mustang. Long story short the cat broke somewhere after the flange that connects the exhaust manifold. I can grab the down pipe on one side and shake it…nothing…the other one clangs around and I can see the cat tube moving relative to the flange. In case you are not familiar with the B8 S4 exhaust, you can see where the cat is here

I called the dealership and they won’t do shit…which is no surprise. I am not the kind of person that will swap all stock parts and pretend like this happened at the taco bell drive through.

Bummer indeed. The root cause is probably one of:

  1. Aftermarket exhaust put too much stress on this joint, which seems unlikely because the downpipes have a flex joint. But it definitely took some finesse to make the tips line up correctly at the valence;

  2. The tune was running lean and heating up the catalyst too much which weakened the pipe. I was running hard at the track so maybe EGT’s just went up naturally and this is what I get. But never heard of another person having this issue;

  3. The motor mounts have failed (which is probably true, they are oil filled and known to fail) and allowed the motor too much translation/rotation which overstressed the cat joint under all the forces imparted by mid-ohio;

  4. The part was poorly manufactured.

Honestly, I have no idea which one is the case.

At this point, I’ve spoken to Ray (who does all the work on Jeff’s car) and he will look into it. Great guy. He advised dropping the whole driveline, based on his experience with Jeff’s header install. I’ve read the cat’s are accessible by dropping the trans and rotating the engine, but honestly, I’m not going to question his thoughts. He thinks this will overall make it easier and quicker. Luckily the Canadian dollar has tanked and he’s in Windsor, unluckily, there is 13% tax. Overall it still works out to a labor rate of around $90/hr.

The plan is then to weld the cat back together. I don’t know. I’m pretty torn on this…Michigan has no smog checks so the smell is probably what will hold me back from test pipes. Keep in mind this is still an every other day DD, plus a car that I might one day sell. I don’t really care about the 20 HP or whatever sound I would gain…BUT fixing the factory cat might just set me up for the same or other issues down the road. Since the tune will probably eventually kill the cats. He will likely reinforce the cat with some splints to strengthen the weld. New cat is 1.1k MSRP.

Ray is a smart enough guy where we will diagnose if the root cause is related to my exhaust. I hope I don’t need to replace the exhaust…would probably go with JHM or Milltek. But again, don’t want this to turn into a 4-5k solution.

Definitely a shitty day when you realize what pay to play really means…but it could have been worse…could have smashed into the guard rail or something. Or blown a motor.

Jake@JHM might have some used OE B8 cats laying around. He sells quite a bit of the aftermarket at his shop.

I would not recommend the Skywagon route. What ever happened to that guy?

OEM cats are excellent quality, so I doubt it was just a bad one. Weird.

Running rich would be far more likely to kill a cat than running lean. In otherwords dumping unburnt fuel into the cats. Running lean wouldn’t cause it unless the ecu goes full retard in protection mode and dumps crazy fuel.

I would just get some HFCs or test pipes. I don’t see why this would affect your exhaust in any way? Just stick with your current setup.

Ah that sucks, i havent heard of a cat breaking other than the catalyst failing inside.

I wonder if this is what is wrong with my car, it sounds like a huge exhaust leak engine side, my apr exhaust has no signs of leaks in the front area, i didnt try and move the pipes like you did.

I do have a broken engine mount, i can see the fluid that has leaked out.

I bought some 034 ones, but have not had time to install them yet.

I was debating going test pipes also, but yes for the same reason as you i do not like gas fumes. One reason i really want an e85 tune so i dont have to smell un burned fuel.

I was leaning to test pipes or gutted stock cats, and then add some metallic race cats to take the place of the front resonators.

The cat section can get super heated on long runs and pushing the car at the track is going to ovewhelm the cat after not too long espically the precat.

There really is no need to drop the motor for a replacement. Your just removing the precat section.

Your in michigan if you want let me know I know several great exhaust guys. Or try countvohn he makes headers for the 4.2 cars and Im sure he would be able to help

You know whats best for you but I wouldnt put back in the precat. There was enough heat to do damage to the pipe emagine what it could be doing to the motor

Wow. I’ve never heard of that happening either.

Definitely curious to the actual cause.

It really sucks though… :frowning:

I can see in one sense running rich would cause ignition within the catalyst (which is how I thought they normally fail), while the lean burn produces higher EGT’s. But I’ve seen how in some cases a very rich mixture will push EGT’s while a lean mixture can also. I don’t pretend to understand this.

In terms of HFC’s, yea, that would be ideal, but no one makes them. 034 pulled the product and JHM has no ETA on availability. Not really liking the idea of test pipes on this car. The issue with the exhaust is whether the exhaust somehow caused this…I doubt it but who knows.

Thanks for the offer Justin. I’ll send you a PM later on tonight. I have no idea why this happened. I did log EGT’s at one time so maybe I should look at those logs.

Are custom HFC’s a possibility? Perhaps you could re-use the stock tubing even and just weld in new cats?

I’m cutting my HFCs out of my JHM headers for my B6 S4. Not sure if they’ll work for you but you’re welcome to them if you want.

Yeah that’s a first I have seen this.

We got test pipes ready to go and on sale:

Best looking pipes I have seen on the market ;D

While you are at it, pick up the motor mounts. The OEM ones suck:

Jake any news on the HFC’s?

Liked the test pipes on my car, just too darn loud.

This is definitely one of the choices I am close to. Just relocate the O2 sensors to your test pipes? Then I guess APR has test pipe software. Do you have any comments about the install?

I would be amazed if you had the same problem.

The last point is pretty interesting…so essentially I could tig a race cat down stream (maybe downpipe), somewhere within the exhaust? And this would help remove the various pollutants such as NO2, NO and CO. That seems desirable. In the sense that I could try out the test pipes and see if I’m ok with the noise/smell. If not, then add some high flow cats which are not involved with the ECM emissions system (due to test pipe software). So it probably would not run optimally in the sense that no feedback from secondary O2…but would perform at a decent enough level to not stink up my garage. That is intriguing.

Install is fairly quick on these cars! At least for us.

Not yet =/

If you are looking for some HFC we can sell you some to put further down stream if you wanted to.

Can you say anything about the approach you use or estimated time? Would the pipes come with instructions if I wanted to install them myself or look for someone local who could? Thanks!

There are parts of the false firewall that come out to gain more access back there. Other than that it is pretty straight forward. You will want some extensions and wobble connections etc… Unfortunately no instructions. If you get caught up you can always give us a call, full time tech support ;D

Thanks Jake…you are making this decision a lot easier if you are saying the install is possible from the top. 8)

Not from the top, but you can get to the bolts

They say a pic is worth a thousand words

The flange bolt is in the right upper corner, this is with a hobo freight camera scope thing.