Help needed with MAF flow values - 2007 RS4

B6/7 S4/RS4
#1

Hello folks,
I’ve recently completed an engine re-build on a 2007 RS4, and I’m trying to learn how to use the VCDS software to check the engine operating health. At the moment I’m focused on on the MAF - is it reporting healthy/reasonable values etc. Below is a short summary of a 3rd gear pull from 3000 to 7360 RPM which I did yesterday. I was logging Advanced Measuring Values 002-1 through 002-4, and 003-3:

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I logged a max of 135.81 g/s before letting off the throttle, but this seems a bit low to me. Based on several threads I’ve seen, a rough hp calculation for the RS4, which has two ECUs, can be made by - (135.81x2)/.8 = +/- 339 hp. That’s 81 hp down from the factory 420 hp value. I’ve not had the car on a dyno, so I’m just using the factory figures as an assumed target for the moment.

Am I doing my math correct - in other words can anyone confirm that the numbers reported via VCDS (135.81) represent only half of the total MAF airflow? Where each ECU only reports half of the total?

Thanks all for any feedback you might have.

Bob

#2

That is an interesting log and I will say I’m no help with the B7 RS4 but something earlier I have logged my chipped C5 RS6 and it has two MAF’s and the computer won’t show over 364.08 g/s combined (G70 + G246 in the RS6 case). Probably a little over 500bhp. But the numbers you see for a stock RS4 or RS6 or any car from manufacturers are crankshaft BHP numbers and not at the wheels so you’ll need to subtract 20~25% for AWD drivetrain losses. Also it would be interesting to delve into Vagcom’s Engine Load calculation as yours is showing maxxing in the mid-80% range and a log on my RS6 is maxxing at a max of 181.2%. These are full throttle runs in 3rd gear. 81 Bhp loss for drivetrain losses would be pretty reasonable on a AWD car.

#3

Good evening Mark,
Thanks for your feedback, and your thoughts are very reasonable. In thinking again about my log numbers, I certainly forgot that no car in stock condition matches at the rear wheels what the manufacturer specs for bhp. Let alone a car which is 16 years old. I finished the engine re-build earlier this year and overall the car drives great, with no fault codes.

Being a perfectionist however, I’m always wondering if the motor is running as well as it could - hence digging into the VCDS platform. I’ll keep poking around to see what I can learn.

Thanks again.

Bob

#4

Understood. The MAF’s can get a little weak without throwing codes too. It would be nice to have a spare to try and see if the numbers are different. I’d log the fuel trims as well as the knock sensors and see if you are getting any timing pulling on any cylinder. Otherwise it sounds like it’s running well.

#5

I’d get an idle log with the maf. This to me has been able to show the best results as there’s so little air moving that you’re going to test the sensor more than if you have a lot of air. Remember there are two banks but if I remember you can access I think both mafs on one data block… But it’s been a min since I’ve logged an RS4

#6

Good morning Justin,
Thanks for your feedback. I ended up removing and cleaning the MAF yesterday, just for the hell of it - it wasn’t particularly dirty. At idle it’s measuring about 2.0 to 2.5 g/s, which seems reasonable based on what I’ve found thus far. At some point near term I may get a new one, and re-log to see if there are any changes.
I’m going to start looking at timing advance/retard as well next up.

I would still love to confirm if I’m looking at the math correct - at 7200 rpm is it pulling in 135 g/s or 270 g/s? I’ve found some threads from many years ago which say 270, but I’m still looking for that RS4 expert to chime in. LOL.
Thanks all…

#7

Generally you’ll see the idle MAF from about 4 to 11. I’l dig though some of my old logs but that’s what I remember. But with all that said the ECU will generally give you a CEL if the MAF is out of range as the ECU will let you know.

#8

Good morning Justin,

Just a few follow up thoughts from last week - as I was originally looking at two issues:

1.) LTFT values for both banks were averaging about +10%, indicating a consistent lean condition, from what I understand. Most threads I’ve seen look for LTFT values to be about 5% or less for a “good” Air/Fuel balance
2.) MAF airflow values at full throttle ( up to 7200) rpm being a bit low (135.81) as you commented on last week.

I ended up replacing the MAF with a new Bosch unit, and now see the following:

1.) LTFT values for both banks averaging 3% to 4%
2.) MAF airflow at 7200 increased from 135.71 g/s to 150.97 g/s - an 11% increase in reported airflow

So, I think I had an aging MAF sensor which was reporting values lower than actual, and perhaps this was contributing to the LTFT adjustments to correct what the ECM was reading as a lean condition. As values are averaging 3 - 4 % now, there may still be some lean issues here, but this is moving in the right direction.

Interesting, at idle I still read about 2.5 g/s from the new MAF, which is fairly consistent with what the old unit reported.

Anyway, thanks again for your feedback - it’s interesting to capture this data and to try to interpret what it all means. One’s car may not be reporting DTC codes, but is it running as well as it could be? There’s the question, right?