Testing MAF

[Flat on my back]

Can't get enough of this techy stuff...

Am i sad for saying that?

Anyway, very interested in having my MAF checked out if poss? ok only 90 20 valve, but it was running lean at WOT on the RR at Castle Coombe.

Sounds similar to the previous discussion.

Thanks.

[ifa]

From AAN workshop manual: Reconnect the connector at the air mass meter.
‒ → Push back rubber grommet at connector of air mass meter.
‒ Connect the multimeter for voltage measurement range (direct voltage) between contact 1 and contact 2.
Note:

Pin assignment is marked on back of connector.

‒ Switch the ignition on.
‒ Specification: 1.2...1.5 V
‒ Start engine and run at idling speed.
‒ Specification: approx. 2.5 V
‒ Fully depress the accelerator pedal and release again (brief actuation).
- Specification: Clear voltage rise to 3...5 V


Mine shows 0 V with pins 1-2.
Pins 1-3 2,35 V at idle.

Should i get voltage between pins 1-2?

[S2central.net]

Useful info Paul thanks again for all your efforts. My RS2 came with a reciept for a 968 MAF. see http://www.s2forum.com/forum/showthr...hlight=968+maf

FOund a mistake in the AUdi source of info that I used last night... Rev 02 attached is more correct - you can see that 3ohm resistance between pins 1 and 3.

I'll post some photos that show the nodes A, B, X and Y on the filament and thermistor if any brave souls wish to whip out a multimeter and their MAF screens.

Paul

[alg]

Useful info Paul thanks again for all your efforts. My RS2 came with a reciept for a 968 MAF. see http://www.s2forum.com/forum/showthr...hlight=968+maf

[S2central.net]

That thermistor is PTC by the way - resistance goes down with temperature decrease - which would smell right. Reduced resistance thru this causes increase in current thru filament which causes higher voltage output from MAF to represent higher mass of cold air passing over the filament (compared to same volume of air at high temperature.

Think I might have to sleep now. Quite pleased with todays MAF explorations

Paul

[S2central.net]

Well I just had to draw this while it was fresh in my head... I'll post pics to help sometime later and add this info to the MAF datasheet at s2central.net when I get it confirmed by Mr. JDS.

Note - you might need to rotate this PDF to get it oriented correctly on thee screen.

Paul

[S2central.net]

Oh nice one John - thanks for popping by...

I contacted John (after a long internet search for a local expert) about MAF tests and calibration earlier today. He is from www.jdsporsche.com and has useful experience on testing similar MAFs on various Porkers. He has written a useful FAQ about MAFs and I shall be discussing matters with him next week with a view to getting data from the S2 and RS2 MAF from his testbench.

Lower MAF o/p voltage for the same mass/flow of air results in leaner running - which at part throttle can be adapted for with info from the lambda probe (within adaptation limits on the ECU). At WOT however, the ECU does not bother with lambda readings so that it can ensure a suitably enriched mixture for the requested welly of boost... So if the MAF is reading low you could be running too lean for safety with an increase in EGT as well.

I have been doing some tests on a MAF here after finding a loose schematic for a Bosch MAF in one of the Audi books but I really need to cut inside a dead MAF module if I am to learn anymore about its internals.

Does anyone have a dead old S2 MAF (even with a ripped out hotwire) they can provide for more tests and internal examination ?

John tells me that he can provide new MAFs on an exchange basis at competitive rates. I did not know that the Porsche 968 uses same MAF (0 280 213 017) as the RS2. John has a brand new one he can start testing with.

John offers a MAF test/check and recalibration service at JDS which may be very useful for us all here one day...

IMPORTANT BIT - Rather than us all plague John with requests can I ask that you let John and I talk thru the techy details before he can size up the task and costs of doing such work for us.

If you are interested in this subject then please post your interest here and I'll do my best to get the best price with John. Initial indicators already look quite good.

Paul

[John Speake]

The calibration of the MAF is critical. The allowable tolerance on calibration is typically +/-3% before the ECU can't adapt. Hot wire MAFs always age in the negative direction. This results is a lower output voltage across the range as has been noted.

A bad MAF will result in the O2 loop getting out of range, and also will affect throttle reponse and WOT power.

The differences noted here of volts at idle for old MAF (1.1v) and new at 1.4% is nearer 16% !

[S2central.net]

It will readapt quicker if you reset the ECU. Disconnect it (or MOTOR fuses) for about 1 minute.

[valjo]

so paul, is it wise to disconnect ecu for while to erase its adaptation because there is quite some differences between old and new MAF and gives ecu changes to adopt to new maf?
or will ecu adopt to new maf without reseting it?

thanks
grega

[S2central.net]

Woah - quite some difference there compared to the older one !

I think the MAFs go out of calibration with age - wish there was a specialist who could refresh them to extend their life as they are very expensive to replace.

Paul

[valjo]

hi!
i get new maf from vagparts today, and i make test for voltage outputs:
engine off, ignition on : 1.4v
engine on at idle: 2.5v
wot: caa 4v

[S2central.net]

The voltage output coming from the MAF is a function of the MAF sensor itself - it is *NOT* influenced by what chips are running. I'll try and dig up a site that shows some Bosch MAF voltage curves from a Porsche - these will give you an idea of what the S2 curve should look like - not exactly though.

O/P voltage increases (non linearly) with increase in airmass flow in range 0-5V.

Paul

[valjo]

@lhd_kid and you are runing standard 3b/aby?

[LHD_Kid]

Tested mine today, just to see if there were any differences....

engine off, ignition on getting 1.41v , so about right...
idling I get 2.55v so spot o I think...
brief blip only getting 2.6v or 2.9v, however, if you blip it so the revs increase a little more, still a blip but slightly longer I can get 3.6v - 3.9v
As far as I know, mine is working ok, so slightly lower figures I reckon are nothing to worry about..... I hope......
Chris