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Discussion Starter #1 (Edited by Moderator)
The air mass meter is a critical sensor and well known for causing performance issues. But don't rush into replacing it until you do these checks.




The signal from the air mass meter is required by the control unit to calculate the required injection quantity and to control the exhaust gas recirculation. The smaller the signal from air mass meter G70 the smaller the quantity of fuel injected.

TESTING (requires driver and VCDS operator)





1. open vagcom / select engine / meas blocks 08 / groups 010 and 002
2. when at normal temp / accelerate from 1500 rpm at full throttle in second gear / at 3000 rpm press log or screen capture as above
3. compare specification / block 4 accelerator position 100% / block 1 air mass drawn in above 700mg/stroke / renew if less than this
4. if constant 550mg/H (predetermined value) indicates fault / switch off ignition / remove connector / switch on ignition / measure voltage supply between contacts as per diagram below





ADDITIONAL CHECKS AND MAINTAINANCE

* Check basics - hose connections from air cleaner to turbo. Any leaks will allow unmetered air into the system and reduce power.
* A loose suction pipe leading from air cleaner to turbo inlet is the most likely culprit. Replace o-ring inside pipe and secure properly. See photo below
* Remove sensor and spray liberally inside with Isopropyl Alcohol or similar to remove dirt, allow time to dry and refit.
* Use electrical contact cleaner to remove deposits off connector plug, once dry apply silicone grease which acts as a good insulator. Remember the slightest improvement in voltage signals can have a dramatic effect on performance as the readings received by the ECU are more accurate.
* Some people unplug the sensor to determine whether it is working or not. Unplugging it will trigger a DTC and the ECU will estimate injection quantities using predetermined values. In theory, if it runs worse then the sensor was working ok and if it runs the same or better than it may need replaceing. Personally I do not think this is a reliable method and should not be used.
* Check wiring for short to one another / short to earth / short to positive / spec ∞Ω


 

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Re: G70 AIR MASS METER (aka MAF SENSOR) TESTING

Brilliant post. Well done.A:
Maybe another that should be made a "sticky"
What do mods think?:*
 

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Re: G70 AIR MASS METER (aka MAF SENSOR) TESTING

He's good that Simon is. :D He's done a few of these now and he always puts effort in beyond the cause. cheers Si T:
 

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Discussion Starter #5
Re: G70 AIR MASS METER (aka MAF SENSOR) TESTING

Thanks for the comments. I know from experience what a painful journey it can be getting these motors running right and by writing a guide it helps consolidate my understanding of it all too. cheers eveyone T:
 

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Re: G70 AIR MASS METER (aka MAF SENSOR) TESTING

Folks,

Whilst you are out in your buses following this excellent guide, it's an ideal opportunity to test your MAP sensor at the same time.

I've written a little guide that can be found in the tech section:
http://www.vwt4forum.co.uk/showthread.php?t=84104

Any corrections and tweaks that you can recommend would be appreciated and I'll update it as necessary.

Cheers,

RS
 

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I realise I'm resurrecting an old sticky here but I got as far as testing the voltages as per the last diagram and I have 12.5V instead of 12V. What is it indicative of if someone isn't getting the correct voltage please? Or is 0.5V negligible in this case?
 

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Hi I've had the van a few weeks now and I have commented on how slow she is and I read it could be down to the maf well it appears that the last owner(bob the builder) had one fitted not long ago my question is this .is it possible to have a faulty one if so why didn't the garage who fitted it notice ? Do they need to be adjusted? Or is it most likely that it is one of the problems that was discussed above in this thread
 

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great write up. This and the N75 and the MAP how tos have been really helpful.

On my van, an ACV, the low pressure pipe (suction pipe) was very loose where it joined the turbo. I have cleaned the connection, but think I need a new o-ring. Does anyone have the part number?

Is there an insert or something in there as well, because it is an extremely loose fit. Just had a workshop do the cam belts, injectors ang diesel pump and I think they could have lost a fitting.

Thanks
Robin
 

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I see this is an old thread/how to, but in reply to robinm's query above, some of the suction pipes (see simon6374's top quality pics)
seem prone to softening and stretching where they fit to the turbo inlet, creating an oval shape to the end of the plastic pipe, causing a loose fit on the turbo, air leak, and dirt ingress. The O rings I have seen were all proud of the groove they sit in, with no wear visible. It is easy to miss the stretch/wear unless you give the pipe a good heave - can help to remove the M6 mounting bolt. The quick cure is to fit a hose clip over it.
 

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Very useful post. The advice about checking the air inlet pipe and the rubber washer at the turbo end was helpful. However I found that the new replacement had little impact on wiggle/movement and fancy that over 17 years the pipe and suffered some wear. This may be a bad idea but a pack of assorted seals from the plumbing section at B&Q produced a fatter profiled washer that fit snuggly but it still needed a jubilee clip to get a good seal. I also cleaned out a lot of oily deposit, put a clip on the breather pipe and replaced the vacuum pipe (? the thin one). And the old dear now goes up the test hill in third rather than second and feels much improved all round.

Prior to this fix the Air Mass Meter was down at 520 but will test again to see if this moves to the 700+ recommended and replace if needed.

T:
 

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The improvement was short lived! Do I have confirmation bias? voltages checked and spot on; contacts cleaned but not tried the silicone grease. A £24 maf from ebay lifted the mg/str reading to about 600 from 515 so still down on the 700! Feels slightly better (confirmation bias again - although the numbers have moved).
 

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Hi folks and thanks for all the great info and diagrams (simon!)

my 2.5 tdi t4 is dropping bout 20% power - i've started looking into suggestions in this thread

The van actually performs better WITH the MAF connected - still not right tho..

using simons guide, i'm running voltmeter tests and have found that G70 AIR MASS METER plug shows 0 voltage from point 2 to earth (should be 12v), same from point 4 to earth (should be 5v). the other two point to point test are fine.


would welcome any advice please (got my diagnostic rosstech gear coming next week!)

thanks all

:)
 

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My van sufdeenly stopped being able to pull the skin off a rice pudding, using this very helpful guide it seems that I am not getting the 12v supply to the MAF plug (I am getting the 5v supply)
it seems to go down the front of the engine and underneath meaning a lot of work to trace where it eventually comes from. The engine wiring diagrams are no use as it just ends at connection "20" Where is this and is there a better diagram of the wiring for the MAF? I am making an assumption that this is maybe an ECU pin number but which one and where is it on the van, there are several!
If I can proved its the oft referred to broken wiring on the engine I can fix this with a bit of stripping down but I would like to isolate the fault first, any helpful suggestions on where to look first?
 

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Been trying to test but for some reason I can't connect the vcds-lite to the engine. No connection reported all the time yet it will test air bag...

Any advice will be very welcome, thank you
 

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Year/model/engine?!?!!?

Without that info....you need Harry Potter to help you. (With his Magic Dip Stick) LOL:
 
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