NefMoto

I've just recently gone to catless downpipes on my b5 s4 that I have tuned to stage 1 currently.  I have noticed a good amount of grey smoke and smell since doing so especially when coming to and idle after driving hard.  My clothes also smell like a weed wacker engine.  I'm also hereing backfiring when revmatching and such but the pipes are non-resonated and catlesss.  My thoughts are it is running rich which is producing the excessive smoke?  Slow oxygen sensors or is a leaner tune needed to compensate?

Have rear O2's been coded out?

You will hear pops and crackles, and it will smell more than with cats.

I had a very similar perception when I removed my cat (1.8t). It still stinks but the AFR reads fairly normal at idle - when it smells.

http://nefariousmotorsports.com/forum/index.php/topic,1160.0.html

Well I can't figure it out, I've replaced the oxygen sensors today and it still smokes but only when I left off the gas and come to idle, very strange.  I'm thinking it's either some oil leaking from one of the turbos or its pig rich from a leaky fuel injector or something.

Definitely sounds like you're running too rich...  What does your WBO2 say?

Oil getting in the pipes.  I guess the cats were doing a great job at hiding my mechanical trouble... Really makes you think about how many cars are running around burning oil and no one knows.  I ended up changing the oil from 5w-40 synthetic to 20w-50 castrol gtx high millage dino oil plus a quart of hyperlube smoke fix and so far the smoking problem has gone away about 60-70% and I've only driven 20 miles so far.  I deffinetely have a turbo seal leak.. :(

Check your plugs for oil fouling.  These cars run reasonably well even with fouled plugs.

I suspect valvestem seals.  Mine cleared up after an italian tune up - I suspect the seals had dried up having been parked for 5+ months in a garage where the temp was over 100 degrees around the clock.

Turbo seal leak, dino oil and smoke fix by hyperlube made 90% of it go away :(

If the turbo seals were leaking it would smoke all the time.

Nope only smokes on engine breaking and coming to idle.  Theres no way its the valves, way too much smoke to be going through the combustion chamber.  It drips off the exhaust seals on decel and smokes up.  But either way thicker dino oil did the trick and the smoke is gone.

That's classic valvestem seals.

In my case my valvestem seals were leaking enough to foul the plug and lay down pretty impressive fog.  It was not something I even knew was going on until I pulled the cats.  I've been running 15w50 Mobil 1 for the last 120,000 miles or so, before that it was 0w40 for about 50k.

I ran a borescope up the downpipe and the turbo did not show any signs of seal failures.  Compression and leakdown were great.  The cylinder walls looked fine and the piston crown did not indicate poor ring performance.

After some hard driving the issue went away.  Of course I had already ordered a set of valvestem seals at that point.  Here's what the cyl 5 plug looked like, with cyl 6 on the right.

(http://i.imgur.com/Zv5rY.jpg)

Jason, is your car a b5 audi s4 like mine?  Also, you say it went away with hard driving... so you didn't even change to a thicker oil or you did?  So your saying the pressure differences with out the cats have something to do with it and the valves just get used it or what?

Yeah, 2000 S4, with K04 hybrids.

Since it's 115+ degrees here for a few months every year I usually park the car for a while and don't drive it.  Before that I did a bunch of cold start and idle tuning, which is horrendous for the cats.

We had about a month of 80 degree weather, so I pulled the car out of storage and noticed it had a slight lifter tick.  I took it out and the ticking went away after a few minutes of transient loads.  I did some data logging and noticed my EGT's were way high under WOT, so I removed the cats figuring they were toast.  Immediately it started smoking on startup, and on engine decel.  The cats were burning all of that oil off.  The amount of smoke was embarrassing and I figured the engine was toast.

That's when I checked the plugs and noticed 6 was oil fouled.  Compression and leakdown were fine, and there was no internal damage I could see.  I had about 6-7 track days on the oil so I changed it, threw a new plug in cyl 6, and went and ran the hell out of it.  It took about 100 miles of hard driving, but it cleared up and it does not smoke any longer.  I make sure to drive it once a week now.

I did order new seals, and let me tell you they are extremely small - so its possible that over time the seal's tensioning springs relax, or the seals themselves dry out and shrink.

I wish I had taken video of it when it was at its worst.  Here it is after it started clearing up.

http://www.youtube.com/watch?v=FHpfCE6eQRs

Haha wow, that's exactly what my car was doing but even more smoke!  Well it make sense that this smoke fix and heavy weight oil have fixed it on my car now... I just feel bad for how thick of oil i'm putting everything through now..

Yeah, when I'd do a third gear pull and lift, it would literally lay down a thick fog of smoke.

Here's what the valvestem seals look like... Next to an M&M.

http://i.imgur.com/e578R.jpg

FYI, I replaced the turbos, all the smoke is gone... I don't know if this was a different issue for you Jason, but I had the exact symptoms of your video, and now that I have the K03s gone and the franken's in, the car doesn't smoke, smell, nada.

I haven't had any smoke issues since I started driving the car regularly.