EUREKA Moment ?

[S2central.net]

Well not quite but its a wee bit of (purely untested) theory that came out of another restless nights sleep in the search of how to extract airflow information from our MAFs.

I've always thought that the LOAD parameter in VAG-COM must relate somehow to airflow and I'm more convinced than ever that I'm right.

It reflects a %age value roughly 25-100 % from idle to WOT... and I now think that is a %age of 5V (FSD) on the MAF input signal.

Then I find this graph for the Bosch MAF on a 4.6L Mustang and I do some quick airflow calculations that give ~100kg/hr at 800rpm and ~920kg/hr at 7000rpm.

http://www.mustangworks.com/articles...mages/fig2.gif

Note the NON-linear shape of the MAF output curve.

SO if we can get the output curve for the S2 and RS2 MAF then we finally have a way to measure air consumption at the MAF by the LOAD parameter in VAG-COM.

I wish you could see the grin on my bake .... until someone proves my untested theory wrong


Paul

[Mihnea]

Paul, the load %age in VAG-Com is definitely not airflow. it is an internally calculated load value, derived from MAF but very very very very far from it and IMHO not really of great use....

hth

Mihnea (still at Doug"s cuz I missed my plane yesterday dangit)

[S2central.net]

Dammit Beavis - why didn't Bosch just publish this info instead of leaving people like me to rack their brains all the frickin time ?

BUT am I right in saying that the MAF output graph will give the mass-flow info I'm looking for by probing the appropriate pin ?

The output graphs for S2, RS2, SQ or M5 MAFs would be mighty useful information. Do you have anything like that - can you share it for my sanity ?

Paul

[Mihnea]

Paul,

If you log the MAF output voltage, you'll have an idea of what's going on. Personally, I've never really felt the need to log MAF, not even when tuning S3s or RS4s where the actual MAF value is being displayed with VAG-Com...

I don't have any output graphs, IMHO the easiest way would be to flow bench them...

Another thing: the S2 MAF is the RS2 MAF is the S2 MAF electronically speaking. The flow rating must be around 800-850 kg/h, and AFAIK the SQ and M5 MAFs can measure around 1100 kg/h...

Bosch keep lots of their internal kitchen things for themselves and Audi, and MAF output curves are really not easy to come by...


Mihnea

[S2central.net]

Oh aye - its dead easy to flow-bench them - if I had a flow-bench !!!!!!!

Seriously though - where could we get access to one ?

I shouldn't imagine it would take long to get a plot of mass flow against output voltage from a bench. I'd pay for time on the bench and donate a MAF for testing.

Getting such a graph would also be great for MAF fault diagnosis as they are very expensive to replace on the pure hope of fault resolution.

Cheers,

Paul

PS - Can you divulge how the LOAD parameter is generated in the ABY/ADU Motronic ?