Bad maf vs good maf info, with logging

[Nick Gustas]

Warning, no notes, all memory, and it's been almost 2 weeks




My car seemed like it was down on power, so I checked all the hoses and hooked up the vag: no codes and the car was making normal boost.

So I started by logging data block 120, torque:


Not good, max torque was only 315nm, and that was just a blip at initial turbo spool, it settled down to the 290s and went down from there as the rpms rose. I could have sworn the car could pull 350nm easy, sure enough, old logs proved me right.

I checked out mass air flow, it passed the Bentley idle flow test, so I ran all of the other stationary vehicle tests in the manual, o2 perf, cat perf, blah blah, they all passed.

So I went out for a run, block 002 I believe;


Not good, old logs showed I could pull 200+ g/s easily, now I had trouble getting 170 g/s and most of the time it was under 150.

I checked o2 learning, a low 100s block, I forget which one, +-4% was acceptable, and the numbers I was getting weren't calling for a bad maf, but a fueling problem, perhaps a typo?

I think 25% was the upper limit.


I go back, run/rerun more tests, they pass.

I check o2 voltages for a sanity check, the more active sensors are pre cat, and post cat sensors are supposed to be for long term trim.

Waaay lean, bad bad bad.


By now I'm concerned, no dtcs, and a slow out of spec car. I unhook the maf just for kicks, hey, it started, seems quicker too.

I check the o2 voltages again, this time, no maf:


I leave the car this way since at least it wasn't running lean and pulling timing like crazy. I call around and try to buy a maf: $330, no thanks. I setup an appointment for a warranty replacement. I leave the dtc and CE light that developed when the maf was unplugged.

I pickup the car the next day, they had determined that my maf was defective and replaced it. Of course the car is perkier

Now let's see what the laptop had to say about it.

Wow, good g/s numbers without even needing to force it.


Good o2 numbers at part throttle:


o2 numbers through a high rpm shift, very good:



Most importantly, my torque was back up and no longer had the little peak at the beginning.

[Kriation]

How many miles to the bad MAF?

[Lehigh]

[Nick Gustas]

[Nick Gustas]

[Lehigh]

[Nick Gustas]

Info
Purchase

[Tostao]

So I can try to reproduce on mine and check against your results.
(I am guessing WOT on 4th or something like that??)

Great job btw. makes you wish Audi had better diag./checkup routines uh?

[Nick Gustas]

either gear, I used 6th for some parts of the torque runs, you just need load. Look for 200+ g/s indicated, 340+ torque in the midrange, and normal .55 to .7 bar boost. Ambient temp was around 50F, and iat was around 70-90F.

[LMDA1]