Buff of black smoke after sitting for a while?

B6/7 S4/RS4
#1

Been trying to figure this out for about a month now, but after the car is up to operating temps and it’s sitting still idling for a while (like at a traffic light or in a drive thru), if I haven’t touched the gas for a while and then I suddenly blip the throttle like I’m about to engage 1st gear, the car will belch this big embarrassing cloud of smoke, and it is SUPER rich unburnt exhaust. Smells like an old boat starting up, or a cold 2-cycle engine. It has a JHM 91 tune on it, their IM spacers, and the TB coolant bypass, and VAG COM is not showing any codes.

Engine-related things I’ve replaced:

  • HPFP’s
  • Fuel filter
  • NGK Spark plugs
  • Air filter
  • O2 sensors (all four are brand new from Bosch)

Also, as long as I’ve owned this car (2 years), I’ve noticed that if I’m just cruising on the highway for a while and then suddenly down shift and floor it, I will clear out the local mosquito population with the cloud of black smoke behind me for a few seconds. On track, the car runs fine, no smoke.

I sorta seems like a bad fuel pressure sensor or regulator, or maybe some bad injectors, but the smoke will come out of both tailpipes equally, for what it’s worth. My best guess is it started doing the puff of black smoke after sitting for a while thing about two months ago when I ran a bottle of Seafoam through the gas tank. Sometimes I think it’s a bad injector, but the car starts/idles/runs fine, short and long term fuel trims look perfectly good in VAG COM, and no misfire codes. What should I try next? Fuel pressure regulator and/or sensor? MAF? TB? Get the injectors cleaned? It kinda worries me when I see that occasional cloud behind me, would appreciate any input.

Thanks!

#2

Welcome to the forum FWP!

Did you change the fuel filter after the seafoam? Just curious

I don’t think it would hurt to get the injectors cleaned and flow tested. My personal plan was to buy all new injectors, get my old set cleaned and then sell them to the 2.0t A4 guys. They are basically an upgrade for those guys who want to run a larger turbo.

#3

Welcome.

It’s always hard to tell exactly what the cause is. Haveing no codes just makes it harder. Your right tho just because you don’t have codes dosen’t mean you don’t have issues.

A few questions to help out. Do you have cats on the car.
Also is this something that the colder weather has made a bigger issue on. Did you see this in the summertime.
If you Rev the motor twice or more will the car kick out black smoke each time after or just one time.

#4

I may buy all new and have them flow tested so that they’re a matched set, if this continues.

#5

I have Milltek cat’ed downpipes on the car, but as part of “diagnosing” a pinging issue I was having with my JHM tune, I was told to gut them or replace them with catless downpipes, so I gutted them. I am really regretting that decision now because the exhaust always stinks now, it was a HUGE PAIN IN THE ASS to gut them, and it made no difference (even the airflow numbers past the MAF were nearly identical). I started noticing the smoke about two months ago when it started to cool down here in Phoenix, but it was still hot, and it’s still doing it. If I see it do the smoke when I rev it once, if I rev it again, yes, it’ll spew smoke again. But then after idling for another minute or two, if I rev it again it usually won’t do it again. I feel like something’s getting stuck, like a fuel pressure regulator or something, and then it fixes itself.

#6

You might consider checking out your coolant temperature sensor. Mine failed and caused hard starting issues. Like trying to start a cold carburated engine with no enrichment. Yours might be failing in the other direction, causing an over rich mixture after start up. Good luck.

#7

Have you tried to buff it out?

#8

Sorry to hear that. Lots of the technical guys have moved on or just plain left AZ. The more technical guys are over here more and help out. This is why AZ blocks any links to this site. What people get is a bunch of guys just throwing ideas out there on AZ.

I have a thread on the RS4 investigation. Its called the RS4 investigaion thread. Starting with pinging rs4s a large amount of rs4s ping stock. Your just not moveing the motor as fast on a stock tune as you are with a JHM tune. The faster the motor the more counts of ping persecond.

Part of whats been found is that the RS4 can have a failed or failing injector. Lots of the injectors are out of ballence with the other injectors. This can cause a lean spike until the injector gets enough pressure to get going. this is one of many things that will cause ping issues on some of the cars.

as for the black smoke. Its actually normal to get some black smoke on free revs when the car is at idle for a little bit. think about it. The car isnt moving and air isnt moving past the block. The block heats up quickly and if the block gets too hot and you free rev the throttle the car will run rich after a few RPM of free rev to keep up with the needed demand of fuel so quickly. Add in dence air and the air charge gets more mass. The car responds with more fuel and when more cooling by adding more fuel.

This isnt to say you dont have an issue. From the sound of it you need to look further into the car. It sounds like your on the right track tho.

When was the last time you changed your maintanence parts like fuel filter plugs etc…

#9

So I read what you said and two things stand out to me. I bolded the two sections that I noticed. Both of those circumstances are a rapid transfer from a prolonged period of very low load/high engine vacuum to a high load/low engine vacuum.

Since you notice the black smoke then it would seem like your engine is either not getting enough air or it is getting too much fuel during that time. Much like how a modified diesel pickup truck will blow black smoke when they stomp on the go fast pedal from a slow speed.

For diagnosis, I would really love to see a log where you go from idle/sitting still at a long traffic light and then accelerate in first gear to redline along with a straight up 3rd gear pull from like 1,500 rpms to redline. The measuring value blocks that I would want to see are channels 3, 103, and 140. That would give the air mass reading, throttle percentage, low side fuel pressure, and the high side fuel pressure specified/actual values.

#10

Yea, injectors are on my list of to-do’s the next time I do a CC. And I hear what you’re saying about the smoke, but if you saw it, you’d think there was something very wrong with my car. I’ll try to get it on video I guess, but it’s pretty random when it’ll happen.

#11

I will try to get those logs here in the next few days. What about the MAF sensor? It’s one thing I’ve never replaced.

#12

I would rather not throw parts at it without doing a little bit of quick and easy diagnosis. That seems like a waste of money, especially since logging those values is extremely cheap in comparison.

Those logs would give a better idea of what the MAF is reading and how much the throttle is opening. I have seen MAFs not read correctly and also throttle bodies that don’t open smoothly and/or all the way.

If you have not cleared the fault codes in a while then it would be helpful to see the long term fuel trims. Go into channel 32 of both 01 - engine electronics and 11 - engine electronics. 01 engine electronics shows bank 1 and 11 engine electronics show bank 2, I think.

If you are feeling up to it then do a basic settings test of the throttle body too. Take the MAF boot off, put the key in the ignition and turn it to ignition on but don’t start the engine, physically extend your vagcom cable and laptop as close to the throttle body as possible with the connector still plugged into the OBD2 port so that you can see the throttle body and the laptop, go into 01 or 11 engine electronics (I forget which ECU is responsible for that test), basic settings, channel 60, click button to turn on the test on, and watch the throttle body move. It should go from closed, to open, and back to closed. You are watching for any hangups or shaking in the movement.

#13

I did clear codes after I installed the new O2’s, but I’ll check it out today, and I’ll also do the TB test, I’ve always wanted to know how to test it to make sure it’s operating correctly.

#14

Here’s a video of what the TB does when I run the test -

https://youtu.be/tp4F5QnVnjM

#15

Here’s a better video, shows what it does at the end, too -

https://www.youtube.com/watch?v=A5er7lS6S3A

#16

Looks like mine’s fine, looks exactly what the TB does in this video - https://www.youtube.com/watch?v=2zrmhDw_v7Y

#17

Ok cool. Still need the logs and the long term fuel trims to better understand things. It is cool to see the video.

The Rosstech video was cool too. I haven’t had to do that throttle body basic settings test on a B8 car with a vagcom yet. Also logging a Siemens style B8 car like a B8 S4 or B8.5 RS5 is weird to me when compared to the older B5/6/7 cars.

#18

What did you want me to log? Long term fuel trims are actually looking very good. -1.5% idle and 2% partial.

For what it’s worth, I did some searching and this guy seems to have the EXACT SAME issue as me - http://audirevolution.net/forum/index.php?topic=184.75

#19

Just to add, the part he’s referring to in this post - http://audirevolution.net/forum/index.php?topic=184.msg3621#msg3621 (the non-return valve down in the V of the engine) is a part I had removed a few months ago the last time the IM was off to show Blake here in Phoenix (koolade9) and while it was out, I cleaned it through and through with gasoline. I wonder if it’s messed up?

#20

[quote=“FWP,post:19,topic:8156”]
If you could transpose our text exchange today, that would save me another rant about our PCV system ;D