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wb131988
18-04-2008, 12:22 AM
Hey,
Found this on another site: 'In the engine computer pull up group 003. Here you will see fields for MAF specified and MAF actual. From 2000 RPM in 3rd gear, accelerate with the go pedal completely depressed. The reading in the actual field should track with the specified field, and should go over 800 mg/H. In reality, the “800” reading needs to be sustained and not decay. This test should be performed under WOT and under a heavy load such as running up a long hill. If it does not the sensor is bad. Replace it.'

How exactly can you accelerate though if the throttle pedal isn't pressed? :confused:

Thanks for the help
Dan

dansansome
18-04-2008, 08:46 AM
by saying depressed they mean pedal to the metal/step on it/etc

depressed means to press down, awell as "in need of prozac"

hth :)

Dan

Crasher
18-04-2008, 09:37 AM
And at the end of the day it is a pointless test that doesn’t work. The only sure way to test an AMM to see if it is faulty is to fit a genuine VAG dealer supplied part and hope it works. I keep them in stock now (the common ones) so I can test the car with a new one and take it back off it if doesn’t work.

That VAG prescribed test can also be very dangerous to carry out, you MUST have a second person to help or use the VAG-COM log function.

I_am_stealth
06-05-2008, 12:21 PM
Why do you say "pointless test that doesn't work?" Your comment is absolutely wrong, unless I am missing something.

Crasher
06-05-2008, 12:47 PM
Why do you say "pointless test that doesn't work?" Your comment is absolutely wrong, unless I am missing something.

It is pointless for a mechanic to spend an hour or so (maybe £50 or £60 at an indi or £107 at Audi as examples) testing a part that costs that much to buy. A quick rule of thumb is no power, no codes = new AMM and in the vast majority of cases it works. Also I have seen numerous AMM’s give figures well within spec but that are still faulty.

wb131988
06-05-2008, 02:11 PM
thanks for all the replies! I will be ordering the part soon :)

I_am_stealth
06-05-2008, 02:31 PM
From a mechanic's point of view, you might have a point, but usually "how to"s on the web are not for you. ;) . I assume mechanics use different info databases, instruction manuals, etc, have access to much more info and tools...I wish i could get to that sort of info...:D

Therefore again, I disagree with your "pointless test that does not work" comment.
It is a trivial test, if one has a laptop ( most people do) .Could be done under normal driving conditions. If also logging the boost pressure A LOT of information can be obtained. One could argue that you could simply disconnect the MAF and see what happens. I wouldn't like to give percentage figures, but in MANY cases you could diagnose a faulty MAF this way.


WB131988, out of curiosity, how did you come to the conclusion that "it's the MAF"? I 'm not suggesting it isn't, but you also might have an EGR stuck open for example....

petercooper
16-05-2008, 09:05 PM
I have had quite a few faulty air flow meters over the years.
One of them running so bad that it wouldnt rev above idle and wouldnt pull away.

An interesting thing to note is that often when an air flow sensor is faulty the car will run nearly perfect when the sensor is disconected.
Thus aiding diagnosis.

Hope its of use


Peter Cooper

I_am_stealth
16-05-2008, 10:20 PM
It depends on the ECU, on AHU engines, for example, if you disconnect the MAF will be almost dead, similar to a limp mode. On newer models it will behave like you describe.

Crasher
16-05-2008, 10:46 PM
Disconnecting the AMM/AVM (MAF if you must, VAG do not use this TLA) just logs a fault code that will confuse the situation for a mechanic when they perform a fault code read. I tried this on an A4 2.5 TDI q 180 yesterday just to prove this, it made no difference to the situation as it was failed injectors. I will say this again, for Gods sake DO NOT disconnect the AMM unless you do a fault code read first, all it does is make the task of diagnosis take longer when a professional takes over. The ONLY easy and true test of an AMM is to fit a new exchange VAG unit and see what happens.

chillin_uk
15-05-2009, 03:44 AM
Hi been on this site a while but havent had the need to use it, sound like i am having same issues,
one thing, well few things i dont understand, SORRY FOR BEING THICK, but what are all the abbreviations you are using? AMM / MAF / AVM ????and what are symptoms for each one...my problem is,, car drives fine, but quite a lot of black smoke when i accelerate,
and occasionally goes into limp mode but. Any help or advice greatly appreciated.

Crasher
15-05-2009, 11:05 AM
AMM = Air Mass Meter, MAF = Mass Air Flow, AVM = Air Volume Meter and they are all the same thing. AVM is what the VAG parts department call it, AMM is what it is called in workshop information and VAG don’t use MAF, it is an Americanism. If you suspect the AMM is at fault, buy a genuine VAG dealer supplied exchange unit, it is the simplest, most reliable and cheapest way to test it, they cost around £70. DO NOT buy one from fleaBay or anywhere else except the main dealer, there are huge numbers of forgeries out there. Also do not listen to any muppet who tells you to try unplugging it, this just stores a fault code and is not a reliable method of diagnostics, just a tinterweb myth.

I_am_stealth
15-05-2009, 01:08 PM
chillin_uk , if you can't get your hands on a diagnostic interface, then the first thing I would do would be to check the hoses post turbo. I suspect you have an air leak.
Also even a cheap ebay VAG com diagnostic interface will give you enough information to diagnose your problem.
What engine have you got?

sooty
01-10-2011, 08:37 PM
Thanks Crasher for the info this helped me out loads today... I wish people would stop "having a go" at the mechanics on this site, they do not get paid to provide us information so respect what they are saying

Crasher
02-10-2011, 11:21 PM
We are all the sons of the devil!

sooty
03-10-2011, 12:09 AM
We are all the sons of the devil!

My car started playing up the other day.
It felt like it was losing power and was giving out a hell of a load of black smoke from the exhaust.
I went to my local specialist and they diagnosed it being down to a faulty air mass sensor.
As they were closing for the weekend and it was last they said I might just want to change it myself as its real easy to do.
So I got a new one and installed it, drive for about 5 miles and the car was back to normal again.
Then right outside my door I turned the air con on and the car stalled.
Now when I start the car it is struggling and keeps reving on its own.
If I try and move off it just stalls.
I fitted the old one back on and it is still doing the same.

I'll have to get The AA to tow me to the garage in the morning now as I cant drive it :(

Crasher
03-10-2011, 09:00 AM
That's an odd one for a TDI, I would be interested to see the fault codes that throws up.

sooty
03-10-2011, 10:01 AM
That's an odd one for a TDI, I would be interested to see the fault codes that throws up.

Well Mr Crasher the plot thickens...
So I called out The AA this morning. When starting the car now there is a load of smoke from the exhaust but not the thick black stuff like before... Bear in mind the car was driving fine for a few miles after I fitted the new mass air flow sensor. After starting the car it turns over for a few seconds and then just stalls and throws out this smoke.

The AA guy asked when I last put fuel in the car and it was just after fitting the part, I just put in £20 into an almost empty tank.
He said the smoke smells like petrol and smelled inside the fuel cap and said it smells like petrol in there also... They offered to fix it for £140 but I said I'd rather go to the garage (giving it was playing up before and I want to get to the bottom of all the problems... I didn't mention it was playing up before otherwise I would not have been able to call them out).
So I got him to tow me to my local specialist (they are well known but I cant mention them as they are not a Forum Sponsor) and they are now investigating, I told them to take their time as I don't need the car for a few days as I'm working nights.

In the meantime I went to the petrol station that has just changed over franchises from one company to another... Lucky they found my receipt even though I paid cash (thanks to my Nectar card lol). It clearly shows Diesel and the station owner confirmed that they have not had any other issues reported and that the tank for the pump I used was filled up that morning with Diesel and it is tested on 3 routes before going into the tank.

So I'm off to bed after my long night shift and I guess I'll find out what's wrong with it in the end.

Hopefully they are all wrong and it is something minor but I doubt it giving it didn't sound too healthy... Fingers corssed

sooty
06-10-2011, 04:16 PM
Got the car fixed... It was NONE of the above in the end.

They said the exhaust relay valve had gone and this also caused a blockage in the diesel filter which is why it kept shutting down.
Had the ERG valve replaced, said it is common on the BLB and they replaced the fuel filter under warranty as I had only just had it serviced a few months ago.

Crasher
06-10-2011, 05:47 PM
EGR but the valve itself or the solenoid?