MAF - Air Flow Meter

[hotshot 0]

Can anyone support this:-

Yesterday eve I jumped in my VR6 to leave work, the engine started and as i tried to reverse it died - just like i had stalled it. I tried again... same thing. So i started it for a third time and tried to rev the engine - it wouldn't just died, but there was the most pungent smell from the cat. I had a bit of a fiddle with stuff under the bonnet but made no progress. I called the AA who arrived pronto (Well done the AA). He unplugged the MAF and the engine now has some power. None at the bottom end (have to limp away from lights, junctions etc) and the fuel consumption is all over the place.

I have assumed that the MAF must be faulty and that i should get a new one (ouch £321 from main dealer). However whilst ringing around i have been informed that the action of discoonecting the air flow meter disables many of the sensors and the ecu is placed in a 'limp-home' mode. thus it might not be the MAF at all! The only real way of knowing is to connect up the VAG-COM (see previous thread)

Has anyone any views on this theory.

Cheers

[jcorallo 0]

It doesnt disable the other sensors.

If you disconnect the MAF, the ECU uses the Throttle Position Sensor input as a substitute so that the car will still run, and vice versa.

You shouldnt just buy a MAF without getting a diagnosis from a VW garage or a Bosch expert. Using a VAG-COM is OK, but you still need a certain level of skill to interpret the results - so proced with caution!

Jules

[VRmonster 1]

well when my maf is disconnected the car just stalls out, nothing kicks in to make the car run. is my throttle sensor nackered, or is it jus a difference between obd's? im on obd1 btw

[DundeeDub 0]

same happens on my ob1

[FishWick 21]

MAFs are notoriously difficult to diagnose properly. The ECU will only code a MAF if the following conditions are true:-

Short to Ground

No Signal - i.e. unplugged, severed wires, totally dead etc.

Implausible signal.

What affects most of us is a MAF operating out of range, i.e. not quite rich or lean enough. The ECU won't detect MAFs that are operating out of range. This is true of both OBD1 and 2, in fact it's just one of a many bugs in the Bosch M2.9 firmware.

I've had a couple of OBD1 hotwire MAFs put on an oscilloscope at my local Bosch agent and the waveforms looked normal, but it made the car run like shite. Even the Bosch engineers admitted the MAFs are very fickle, bloody impossible to diagnose with structured testing and cause many, many cars that use them running problems.

I'm on my 3rd MAF now (£150+VAT from Bosch Direct) and I think I've found a good un at last.

[hotshot 0]

How do you get a MAF direct from Bosch - is there a number to call or a website or what? I have located a used one (same part no etc) for £25 + P&P +vat its got to be worth a go for that!!

[hotshot 0]

It turns out that the part nos are different

i have a 021906462A

and they have a 021906641 - anyone know if they are compatible?

[FishWick 21]

Yes you must match the part numbers as the sockets are different with each MAF type. OBD1 uses the long 6 pin connector, OBD2 uses a shorter connector. OBD1 has a metal plate attached to the MAF body, OBD2 has a little plastic protusion from the MAF body.

For the East Anglia region, MJS Services (Bosch agents) in Ipswich (01473 212594) supply OBD1 MAFs at the price stated above. £150 exchange (new internals, old plastic body) or £200 for a completely new unit.

I'm not sure how much the OBD2 mafs are tho.

There's no point in spending £50 on a new plastic body in my opinion and the exchange ones I bought appeared to be brand new anyway.

Kev

[ Edited Wed May 19 2004, 08:12PM ]

[ Edited Wed May 19 2004, 08:12PM ]

[VRmonster 1]

just wondering, although the connectors are different. would it be pissable to use the wiring of an obd1 on an obd2 maf. so i would cut the obd1 wires and fit an obd2 connector and maf, in my 93 car. or do yhey have a different amount of wires?

[FishWick 21]

I'm not sure if it's pissable, but I hear it is 'possible' though, LOL! Sorry, couldn't resist!

Although the OBD1 (hot wire) MAF has more pins than OBD2 (hot film), 1 or 2 of them are redundant. So in theory, you should be able to use the wires from the OBD1 loom and splice them into an OBD2 connector, if you can find one from somwhere.

I've never tried it but I have been told it's been done. I'm not sure if the hot film behaves differently to the hot wire either, so it'll be a trial and error thing. The film MAFs are more reliable though.

As an aside, our American friends on the Vortex site have discovered that the MAF internals from 1999 Golf GTi 8V are exactly the same as the OBD2 VR6 internals. And how much is a Golf MAF? £40!!!

Someone on that forum has successfully swapped internals over, which is bloody going and highlights a daylight robbery issue at VW - charging us £321 for a MAF that's the same as the £40 Golf one.

[VRmonster 1]

ha ha, thats one of my funniest typo's. lol. and i think im going to source myself a bit of gear now.

[hotshot 0]

This is starting to pi$$ me off now...I obtained a used MAF (exactly the same part no.) and fitted it (2 min job). Now i have a differnt set of symptoms.

initially if you remember with the original maf connected the engine would start and idle but as soon as you touched the throttle it would konk out .

Disconect the MAF and the engine works after a fashion (its gutless pulling away in generally down the bottom end) its not to hot allround but that the worse bit.

New (2nd hand) MAF and the engine starts, it seems to rev and for a few seconds all seems well then when iddleing it speeds up, slows down, up, down, up, down and then eventually konks out with a bit of a pop (also there appears to be lots of clicking going on under the bonnet - relays or something).

Do you reckon its just another duff MAF or something more sinister????? :!

[FishWick 21]

That doesn't sound too clever. I think you really need to get that motor scanned whilst it's running and see what the ECU is complaining about. If it moans about mixture adaption limits being reached, it's probably the MAF. It could also be the cam position sensor as that's another favourite. If the car ran fine prior to the MAF going south, odds are your replacement one is duff aswell.

Have you checked the other thread about who has VAG-COM in which geographical area?

You could try replacing the ECU and fuel pump relays for good measure too. I've found that helps with peculiar behaviour like yours is suffering from.

The ECU relay is no 109 and the fuel pump one is numbered 167 if my memory serves me well.

[ Edited Thu May 20 2004, 07:24PM ]