Running out of ideas...

B6/7 S4/RS4
#1

Ok, so as some of you know, once in a while, I’m experiencing some bogging when accelerating.
Initially, JHM and I thought it might be related to the fuel trim levels and therefore tried a few different ones.
JHM’s 3rd tune nailed it spot on and now the fuel trim adaptation numbers seem just fine (from about 7-8% when babying the car and 0-1% when punching it hard which seems to be inline with the tolerances, i.e. doesn’t set off any CEL when on the low side and doesn’t run rich (i.e. no negative numbers on the high side).

The tune is now considered good (and the bogging was drastically reduced).

Now, the bogging ONLY occurs when:

  1. The car has been running over 3k rpms for at least 10-15 minutes (i.e. hot).
  2. Between 2k and 3k rpms

In other words, I’ll drive the car for 15 minutes at around 3300-3500 rpms on the highway, and when I use the offramp (i.e. slow down) and then accelerate again somewhere between 2k and 3k rpms, the bogging kicks in. Above 3k rpms, it seems ok.

What’s been done so far from a mechanical/hardware stand-point (all to no effect).

  1. Throttle body swapped from another car.
  2. Intake manifold swapped from another car. (both my own TB and IM were swapped back)
  3. All four o2 sensors changed for brand new ones.
  4. Downpipe had a neckdown to 2.2" which was annoying. Replaced with a proper 2.5" all the way through.
  5. Smoke test (no leaks). All PCV system quintuple checked.
  6. Fuel filter replaced.

Again, keep in mind this bogging only happens in very specific circumstances. It’s not something that happens all over the place.

Now, on the more POSITIVE note, the car pulls like mad with the new (proper) downpipe and new o2 sensors.

Here’s a 3rd gear pull log (I hit 878 RPMs/sec compared to saki’s (albeit non-carbon cleaned) stock RS4 of 688 RPMs/sec (saki, correct me if I’m wong on that one. I used the last log you posted) with an average of 780 RPMs/sec and a median of 800 RPMs/sec (and that’s with a box on the roof lol).

https://docs.google.com/spreadsheet/ccc?key=0Aifrh7MAi3ISdG5MVmU5TjlseDZTYUswWmJlcUxkbXc

As for some logs of the bogging, here’s a few cuts and paste (you’ll notice the RPMs are below 3k and the load goes up and down which is me giving it gas, car bogs, then let off gas).

https://docs.google.com/spreadsheet/ccc?key=0Aifrh7MAi3ISdGVjLVcyZ2N1TmR2djFjM2VENHBkaHc

Both spreadsheets are editable in case anyone wants to add comments and such. I have the originals.

Thoughts? Ideas? Suggestions?

#2

How old are your coilpacks? I had that same issue when one of mine we’re dying. It didn’t throw a code but between 2-3k rpm’s I’d get a shudder and it would cut power before accelerating off again. It finally died months later and it threw a code. Replaced it and all was well. If I were you, I’d replace all of them as well as plugs and fuel filter in order to eliminate those variables.

#3

Forgot to add that the fuel filter was replaced as well.
As for the coilpacks…hmm…They were replaced (under the recall) in April 2010 so almost two years old. Interesting. Good suggestion (seeing as it happened to you as well).

One more thing, JHM’s website shows two different types of coilpacks. Which ones should I consider getting? The more expensive $30/per or the normal $22.50/per. I’m going to guess the $30 ones simply because they’re more expensive lol but I don’t know what the difference is. They both have the same description.

#4

Wow 878 rpm per second? HOLY FUCK…my car does 525

#5

Yeah, those bimmers tend to be surprised, especially with a roof box lol

#6

Huh?

#7

Never mind just saw his update.

Hmmm, isn’t that what my did saki?

Never mind, my average was 887 lol.

#8

yeah thats really moving lol. if you can easily reproduce the hesitation, try watching blocks 16-18 (i think) and watch for misfires. could indicate and old coil or plug

#9

NO!!! Buy the 22.50. The expensive ones are from an oe supplier. I had terrible experience on another car with those. You want OEM

#10

And that’s why I asked lol Thanks!!

As for your RPM/sec, what are you down to? 3000 lbs? hehe

#11

Close lol

#12

From a tune stand point it looks real impressive. The adjustments look to be steady and you like to see that. The percentage of change looks to hold very well.

Can you play the throttle and keep the car in a bog situation?
Can you do the bog for the rest of the time you drive the car or will it stop at some point?

#13

The bogging will stop when the car cools down (i.e. I stop driving it hard and switch to normal city driving).
Usually, if the bog comes on, it’ll sputter and if I keep the throttle on, will usually clean itself up within 5 seconds but sometimes, it’ll just get stuck and I have to lift off.

#14

that is monstrous, but that was a peak number, not the average (while yours was 525 average I believe from 3k-6k

still…800 average is retarded fast. My S4’s best log was 560 average. RS4 can’t be compared I don’t think because of the gearing being slightly different.

Axel is the car on 235.40.18 (or 25.4" diameter) tires? Also, I have a couple of coil packs from my B7 S4 if you want to swap them in to your car once you can identify a misfire as Tyler mentioned. They were the ‘good’ ones that didn’t need recalling. I replaced them as they were 3 years old because I listened to 91GL a lot (he replaces everything fortnightly)

#15

by the way axel…you have picked up about 200 rpm/second since we logged your car on the break in tune lol. HOLY MOTHER FUCK!

For perspective, my stock B7 S4 which would run high 13s at maybe 101 was around 425 RPM/sec average. When it was fully modified, in DA -500, 94 octane fuel, 2.5" catless to FI catback with JHM tune, LW rotors, LW crank pulley, intake spacers, it did 560 RPM/sec and ran 12.9 @ 107.8. The gap was HUGE. I picked up around 140 RPM/second with all of that…and gaining RPMs/second at those levels is a lot easier than going from 600-800. This also makes sense becuase when we did pulls that were a nice high rpm starting point for my RS4, it was very close. The one pull when we went from 3rd at like 3000 RPM, you jumped out 2-3 cars and then stayed there as the RS4 got into it’s comfort zone of high rpms.

It just shows you how much there is in a tune on these cars. Really incredible.

#16

It is on 235/40/18 at the moment. As for the coilpacks, seeing how cheap they are and I still have credit with JHM, I just emailed Keaton last night to ship me 8 new ones. With shipping it’ll probably cost me $220 or so. Not a big deal. Thanks for the offer though. :slight_smile:

#17

Ever consider taking the car to JHM. I know it’s far but they should be able to figure it out

#18

lol its not far…it’s insanely far. 2000 miles I think.

He’s in contact with JHM regularly about this, so I’m sure they’ll be trying everything.

#19

I was going to guess coil packs or plugs but i see the others have this covered. I’m interested in the heat factor. I wonder if it could be a sensor that is on it’s way out. The heat could be accelerarting its failure…not positive which sensor(s) could cause a specific RPM range hesitation though.

#20

could someone email me the logs? beemercer@gmail.com