Testing MAF

[valjo]

Stock + Milteck Exhaust and MRC Generic Chip (3B)

i guess that you have changed your maf or you still have first one?

[GeorgeS2UK]

Origional MAF -

I have also checked the TPS (throttle position sensor)

Harness Connected

1 & 2 = 4.7V
2 & 3 = 0.1V idle
2 & 3 = 0.27v - 4.68v open throttle to WOT

1 & 2 = 2310 ohms
2 & 3 = 1020 ohms idle
2 & 3 = 1020 - 2730+ ohms open throttle to WOT

ISV - 11.87v
Visual check - removed ISV from the TB, ignition turned over, and the barrell functions

All seem fine but still lumpy idle and hesitation on initial throttle

Fuel OK
Hoses Checked
Plugs OK
Cleared ECU

Last thing though, if i remove the MAF connector idle is good

[Pirvu Eugen]

I have same setup except the miltek and same idle problems but no hesitation. I will try tomorow to disconect the maf to see what hapends.

[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

[valjo]

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

[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]

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]

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]

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]

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

[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]

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

[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]

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

[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