Method to diagnose bad MAF sensors

[cmore]

I have a 03' RS6 and I am wondering what method I can use to diagnose MAF sensors with a VAG-COM.

I'm trying eliminate one thing at a time. I am not getting codes that would suspect a bad MAF, but I am hoping there is a method to determine if they could be going bad.

This is related to be me down on boost from the other thread.

Thanks,
Chris

[RS6-4dr911]

I'll watch to see if an answer is forthcoming. The first is to log MAF flow and check for the difference between them. I have yet to have someone tell me the definitive maximum deviation but the number 10% keeps being bandied about, although given electronic instrumentation accuracies these days, that number seems awfully high.

This article was interesting though:

http://www.mxcom.net/hearst/motor/fuel/001/072006_04.pdf

A lot to digest. Mine have exhibited some large variations so I plan to check it out.

[cmore]

Thanks for sharing that link. What block did you log to monitor each individual MAF?

[JRS-RS6]

Another Link: http://www.ross-tech.net/vag-com/advertising/DiagnosingA_MAF_TechTip.pdf

[cmore]

Ok, I logged the MAF g/s and it came out to 364 g/s at full throttle, which is a total of the two MAF sensors.

The document says the g/s should be approx. 80% of the HP output of the engine. Since mine is chipped and suppose to have ~500hp do I use the stock 450hp or 500hp?

450 x .8 = 360, which is about 364 g/s.

500 x .8 = 400 and ~36 g/s off what I am reading.

Anyone have an idea?

[RS6-4dr911]

Make sure you're not looking at the single channel that says MAF (Bank 1+2, or whatever the channels are) - that reading will max out at 364. Log the individual banks and add them together. That will give you a higher number if all is well on a chipped car.

Just read the other thread you posted on, your individuals at redline total 421, but the sum max's out at 364.08.

The HP x .8 is a good rule of thumb but don't take it too literally.

[JCviggen]

I'm also wondering about my MAFs, since i have some fault codes that could be related to them. But when logging (stock car) they seem OK...at least they are very close to each other. I'm going to be replacing all lambdas, EGT etc. already when the engine is out and on the one hand I'd throw in new MAFs as well, but dont want to throw away good functioning MAFs either

http://www.greenringer.net/various/wotlog.png