MAF g/s vs 0-5v output

[ibizacupra]

anyone here logged their actual MAF voltage output..?

its a 5v sensor signal by design, and from assorted data I have seen for some bosch MAF's they have different characteristics of voltage to airflow, with nearly none of my data showing a MAF sensor airflow max being 5v.. 4.77v seemed a max on a 1000kg/h mass flow for example

logging a car I have had in, running a bigger turbo, 80mm maf, actual sensor voltage measured on maf during a power run was 4.98v, where max airflow value reported in the damos file for this ecu showed a max 4.88 scaling.. for a higher airflow than actually seen.

292g/s max is what it hits on vagcom, at an actual measured 4.98volts, where software suggests this airflow for 4.88 volts should equate to 348g/s in the code in the ecu



Scaling the software is all well and good, but sensor 5v saturation is saturation I am thinking..

 

[Wilko]

Bill
Is it an s4 maf, but you're running it on a base file originally for a 75mm maf (tt/cupra r etc)
If so, the max vagcom will report on that maf is 297.xx g/s, which is around 340g/s through an s4 maf, so what ever you have done on the code may not have worked with regards to what scaling vag com sees.

 

[ibizacupra]

Bill
Is it an s4 maf, but you're running it on a base file originally for a 75mm maf (tt/cupra r etc)
If so, the max vagcom will report on that maf is 297.xx g/s, which is around 340g/s through an s4 maf, so what ever you have done on the code may not have worked with regards to what scaling vag com sees.

hi John, its a 75mm ID MAF, original to the car in question.
the damos file for the ecu, shows a 4.88v for an equivalent 1253kg/h maximum mass airflow (from memory of the screen shot I saw) - 1253kg/h = 348g/s from my calcs

the discrepency is what currently perplexes me. vagcom max is indeed about that 297.xx number (not got the log info to hand at the mo tho, but pretty sure thats what its reporting.

The physical measurement of the actual sensor voltage out being 4.98v confirms to me its off scale, which explains the way it drives when you run off the sensor scale I think.. fuel dump, coughs.

I have my old ibiza's RS4 MAF tube here to use if needs be, but I want to understand the discrepency between the damos figures for the ecu, and the reported ones in vagcom logging and the measured maf voltage output.

I am pretty sure if you run too much airflow through the MAF the hot film circuit in its attempt to control its temp it will overdrive and "pop", as I have heard happens. This is probably why none of the MAF sensor airflow vs output voltage plots I have seen, go to the 5v maximum.

What did you max on yours when on 75mm MAF? was it this 297.xxg/s number also? You on RS4 MAF now? What does vagcom report your airflows being? Wondering what reported number vagcom access's in the ecu to read.

thx

 

[Wilko]

on an s4 maf which 73mm ID, I max it at a reported 297.xx. Rs4 maf to be fitted when 2l conversion finished.
The ecu is still running a file built around a tt/cupra r code.

Is the reported airflow maxing and then voltage is continuing to rise with no rise in reported mass?

Take a look at http://s4wiki.com/wiki/MAF
and http://www.rs246.com/index.php?name=PNphpBB2&file=viewtopic&p=249298, look at mineas comments halfway down the page.

 

[ibizacupra]

interesting read...

the programmed scaling reported by damos is an airflow to voltage relationship, and the maximum setable is 4.98 volts, where its 4.88 volts max as std in a 210bhp ecu.

Clearly the actual measurement of 4.98 volts is beyond its current internal scale of 4.98v but why vagcom is reporting it as 297.xxg/s is werid thing, as the scale against the voltage is 1253kg/h (348g/s) airflow.. for its 4.88volts scaling and 4.98volt actual

there's discrepency in here somewhere..
GT30R turbo, 2.0bar boost flowing all of this thru stock S3 maf (currently)

 

[ibizacupra]

Is the reported airflow maxing and then voltage is continuing to rise with no rise in reported mass?

I've not had chance to correlate the voltage to maf log unfortunately. dvm strapped onto the wiper arm and hooning it down the local straight road eyeballing it for max volts.. and comparing to the previous max airflow logged earlier. was'nt 1:1 sadly

wish I had my RR now
be so handy

 

[mikepts]

hi all.i have a audi s3 '02 model with a lot of modifications.i have installed a 3,5 od maf housing (3.25 id) with the original s3 maf sensor inside.i have same questions - problems.

i read on my log files with vagcom v8.05 that after 6200 rpm and up the maf sensor is running at 299 gr/sec.

1)about 300 gr/sec is the limit reading value of vagcom for maf?
2)if 300 gr/sec is the limit of vagcom did the ecu read more gr/sec?
3)if i change the s3 sensor with same else (rs4?) can i read more gr/sec than 300?
4)do i need larger maf housing (90mm id)?
5)can we rescale the maps of ecu to change the reading numbers?

i had make same calculations as below

stock s3 maf housing 70mm id (internal diameter)
my maf house 83mm id

so i had (83/70)^2=40.5% Deviation than stock maf case
for 90mm id i will have 65% deviation.

did you suggest to change the housing or something else?please inform me

sorry for my poor english...

 

[ibizacupra]

hi all.i have a audi s3 '02 model with a lot of modifications.i have installed a 3,5 od maf housing (3.25 id) with the original s3 maf sensor inside.i have same questions - problems.

i read on my log files with vagcom v8.05 that after 6200 rpm and up the maf sensor is running at 299 gr/sec.

1)about 300 gr/sec is the limit reading value of vagcom for maf?
2)if 300 gr/sec is the limit of vagcom did the ecu read more gr/sec?
3)if i change the s3 sensor with same else (rs4?) can i read more gr/sec than 300?
4)do i need larger maf housing (90mm id)?
5)can we rescale the maps of ecu to change the reading numbers?

i had make same calculations as below

stock s3 maf housing 70mm id (internal diameter)
my maf house 83mm id

so i had (83/70)^2=40.5% Deviation than stock maf case
for 90mm id i will have 65% deviation.

did you suggest to change the housing or something else?please inform me

sorry for my poor english...

Using a larger MAF tube will drop the velocity across the sensor, so yes it will operate within its 0-5v range... the mapping would need to be adjusted to suit...

 

[Wilko]

An rs4 maf is 83mm ID.
If you are seeing 297g/s which is 5v on an s3 sized maf, then you are pushing 430g/s
If your s3 is still a 1.8t, youd need about 45lb of boost, so 3 bar boost to get that much air into the engine.
Are you sure you dont have an s4 maf which is 83mm od, and 73mm id, so youd be at 330g/s which is just around 2 bar of boost?

 

[mikepts]

i got 2.0+ lt eurospect stroker kit with 83,5mm je pistons, precision pt67 billet turbo,bosch saturated injectors,2 bosch 044 fuel pumps,aeromotive fuel regulator (4,1bar pressure) and i operate almost 90% duty cycle.dbillas mechanical camshaft,1mm oversize ferrea valves and more...

my big problem is with maf.i had a 3,5" od alouminium maf housing with 3,25" id.the vag com is reading about 299gr/sec at 6400 rpm.after 6400 the maf sensor is finish.at 6800-7000 rpm the throttle body is closing because the ecu is reading maximum values from maf.until now my ex tuner had calibrate the ecu for the larger maf and he told me that this is the limit for the motronic 7.5.i doubt to believe it.

thanks for the reply.the ecu is stock.bosch 05(rs2) plugs and hitachi

 

[ibizacupra]

a bit more than a 48lb comp wheel then
83.5mm bores? crikey... very very small contact patch left for headgasket then.

larger will drop the voltage for the same mass airflow as said. what have you got available to you to try this? (sizes I mean)
RS6 uses 2 x MAF's so at some point there is a trade off between not maxing a single sensor and being insensitive to low speed/idle airflows


sounds like a monstor - what does it rev to?

 

[mikepts]

tomorrow i will try one 100mm od 95mm id maf housing.as i saw today the maf sensor finally is the same for s3 - rs4.the rev limit is 8500 rpm for now.

i had installed agu head ported etc,precision water intercooler,aem water methanol,zex direct port nitrous (as this time is inactive),larger fuel rails,2 disc spec clutch,6 speed special gearbox by sqs...and more

at least at 1,8 bar - 6400 rpm i got 299 gr/sec * (83/70)^2*1,34=560 hp.i want to see it at 2,5-2,7 bar at maximum.we will see it.

 

[Wilko]

maf will read to 500g/s, byt vag com max is 360g/s, scaled or not in the code.
So an rs4 maf reads to 66lb/min, which on 2033cc at 6400rpm needs over 50lb of boost

 

[mikepts]

my vag com v7.04 is reading 299gr/sec.did i make same correction with vag com to read 360?

by the way i have set the avcr to 1.9bar and over 6500 rpm 40% duty

 

[Wilko]

With 1.8 bar on your capacity it works
out at 340g/s at 6400rpm, so if your maf hits 297g/s and the ecu originaly had a 69mm I'd maf, you have a 73mm Id maf where the sensor sits.

 

[mikepts]

that's the maf housing of my car

atpturbo.com/mm5/merchant.mvc?Screen=PROD&Store_Code=tp&Product_Code=ATP-VVW-081&Category_Code=VVWFE

 

[Damoegan]

http://www.atpturbo.com/mm5/merchan...&Product_Code=ATP-VVW-081&Category_Code=VVWFE

 

[Wilko]

wall thickness looks prety thick, take it off and measure the id at the sensor.

 

[mikepts]

after some updates i have new results.

with the maf house 95mm id with 2,4bar turbo pressure i read about 296 gr/sec at 8200 rpm...at that pressure the fuel pump (ttrs) in tank it can not reload dahlblack catch tank with fuel.yesterday we think some other thinks to try...so stay tuned.

 

[pinotattt]

MR Green

on an s4 maf which 73mm ID, I max it at a reported 297.xx. Rs4 maf to be fitted when 2l conversion finished.
The ecu is still running a file built around a tt/cupra r code.