Loss of power / black smoke Under acceleration

A6 All/ S6 All
#1

Joy oh joy,

Took the car down for a wash today and noticed on my way down 10 minutes into my drive that the car was not getting full power with decent throttle. Seems to idle fine and not rough so is only under load. Also have noticed under heavy acceleration quiet a lot of dark/black smoke comming from the exhaust only whilst driving. Have scanned for codes and have nothing in there at the moment. Thought it would have grown a code after driving for 1/2 an hour but apparently not. Only other thing I have done recently is disconnected the battery yesterday and reconnected.

Any suggestions on where to look

#2

Sounds re similar to when i had the std inlet flaps intermittantly stuck open, car ran like someone had cut both airfilters off, real weezey and unresponsive. Mine never threw any eng lights, but the intermittant codes did come up. Have you had the inlet manifold replaced? normally a failed one rattles plenty during cruizing - this wont throw codes but ruins your lunch and power…and then wallet to replace.

#3

Yeah have scanned it and nothing comming up yes. Ive heard you can have he flaps removed all together and get remapped to delete them?

#4

This forum has good intel on your options, to buy the intake at home is not even worth considering, also the time it takes to split the mannifold and sort/gut then rebuild was about 2k which is over half the price of getting a new one out of USA from JHM ($2k USA plus shipping) remapping for it is not worth it/not recommended by tuners…how do I know all of this. . . . .I did all of the above bar tuning the gutted manny.

It could be something simple like a Airflow sensor or injector or something else…The inlet manny is pretty distinctive, for me it was super rattly from 1400rpm onwards…like turn up the radio noisey. Hopefiully its not that. You can you tube how to find that out etc

chap

#5

I’m praying to the euro gods it’s not. Frustrating how it’s noy throwing a code. When I bought the car I ended up buying my own scanner. God forbid I’ve listed the car on trademe and it’s off to the mechanic tommorow

#6

Only other thing I can think of is that I filled up with 95 in it normally always run 98 how ever surely it wouldn’t make it that retarded

#7

Ya it could do that.

I had this problem when I first bought the car. Started out with 93 Octane in Canada and dropped to 91 on my trip since 93 wasn’t available… and the engine was not happy at all for a few weeks.

I believe the car adjusts the tune based on fuel quality, senses knock and retard the timing where appropriate.

#8

98 octane is probably the closest to racing fuel you can… dropping to 95 would really cause that? Meanwhile, we run 93 here in the United States. Unless fuel ratings are different US to Euro?

#9

Yeah our fuels are different (in NZ), worse quality than US - our 95 is about the same as your 85/87

#10

Yes North america octane rating is reffered to at AKI or as R=M/2 (research + motor)/2 >
Euro is classified as Motor Octane Number. MON is determined by running test engines at 900 rpm rather than at 600 for north american octane classification.
https://en.wikipedia.org/wiki/Octane_rating
read: measurement methods.

93 is as good as 98 in europe.
Very true that hard to find 93 in canada unless you go to sunoco, and its $$

Thankfully there 93 everywhere in MI, usually completely replacing 91. Some stations have a choice of 91 or 93.
But usually its 87, 89, 93

#11

Ohhh, that makes sense then! Yeah, never a good idea to do to your engine… they’re very… delicate. Lol.

@Greg, the more you know! Thanks for the insight.

#12

What cel if any would you get for bad gas and how long would t stay on? On my last s6 it had 93 it’s whole life but the few times I filled 91 it wasn’t as happy and that was on stock tune. One time I put in 91, and quality may have been worse than usual it flipped a cel, but after about a full tank of new gas the cel disappeared. Never got around checking the car ran well just not as well as usual. Curious if Anyone else experienced anything similar. These cars appreciate 93+ for sure, I wonder if the jhm tune would adapt with vp101, might be fun to throw a tank or two in once in awhile for an Italian turn up :slight_smile:

#13

The car should run fine on 91. that is what the stock calibration is made for and the owners manual calls out.
if it ran so poorly that you got a CEL, either water in the fuel or it is highly oxygenated ie the octane number is very low.
You would get misfire codes if it runs rough on a certain batch of fuel.

#14

Yes, I believe CV mentioned awhile back that we can run higher octane fuel and the ECU will adjust accordingly. I considered it during some of the track days last year, but the cost was so high on-site and I was going through fuel so fast I just never gave it a try. Maybe this year sometime.

#15

I thought I remember seeing a premium fuel only label. Depending on where your located fuel content is different.

Like east cost 91 is more like west coast 93. Some euro fuel is crap more like 87 octane than 91

#16

Yes this is true. With the JHM tune you can add better fuel and the ecu will adapt up a few points. enough that you can feel the difference.