MAF SENSOR ON TDI

clough103

Registered User
Im still on my determined mission to find out why my car is so crap on fuel.

Trying a bit of trial and error, am starting with the MAF sensor.

If i disconnect it what will happen? will the car run default values etc and will it put the car in limp mode or generate the EM light?

cheers
 

19scotty81

Push down and across !!!!!!!!!
Hi, sorry i'm new so you've probably already told people but whats your figures ???????
 

clough103

Registered User
struggle to get 30 in town and if i make 45 on a run ive done well and thats driving it sensibly.

ive got a big thread going called 130 TDI economy and have posted some bits today on the new 'mpg' thread
 

Turkster

W.Bro.Paul 2.0d Q5 Quattro
a new maf unit never hurts the MPG for sure mate, they also have a life span of about 12-18 months depending on your driving style, new air filter is a must at the time of change,
 

clough103

Registered User
well i have cleaned it with contact cleaner but it didnt make any difference. I didnt fancy shelling out for a new one if it isnt going to make any difference. I know on other cars if you disconnect the sensor the ECU runs a sort of default program (in which case if the MAF was faulty the MPG should improve then i will know to go and buy a new one)

This is why i need to know what happens if it is disconnected as i know the Audis are a bit complicated and i didnt fancy buggering something up
 

paul20v

Audi fanatic
If you unplug it yes it will go into limp mode
i dont understand what you are going to achieve by doing this to be honest .
 

clough103

Registered User
i will explain by giving an example, simple really.

My other halfs Punto JTD had a MAF sensor problem. MPG was really poor and it wasnt running its best. On disconnecting the sensor the car runs a default reading stored on the ECU and thus the car suddenly became a whole load quicker and the MPG went back where it should. Thus indicating an obvious MAF problem, changed MAF sensor plugged back in and voila Punto running as it should once again.

This is exactly what i was hoping to achieve once again by simple free DIY stuff to find out if the MAF is causing the poor MPG on my A4
 

quattro tony

Registered User
I can see where you are coming from as ive disconnected the maf on some cars that were dead and noticed a difference that led me to believe the maf was at fault, but i have to agree with paul20v if you disconnected yours i don't think you will find it makes an improvement unless your mass meter was shot.The only way to check them properly is with diagnostic like vag com where you can compare the values of the mass meter.
 

paul20v

Audi fanatic
Limp Mode
this is what happens if you disconnect the audi maf
it will not rev above 2k
so you will notice a difference but its not going to help you .
 

paul20v

Audi fanatic
try another unit on the car,
Not having a dig but i would never swap out electrical components
you never know it may be the car or wiring at fault and then you destroy the swapped part too
not that im saying thats whats wrong here its just air on the side of caution when swapping bits from another car .
 

clough103

Registered User
i wouldnt know where to get another one from without actually buying one. will have to get it plugged in at somepoint and see what comes up i guess
 

Cheshire-Autotech

Mobile Remapping & Diagnostics
VCDS Map User
Clough103,

A couple of things to try, breezing thru the thread briefly, others have suggested I see... (sorry to repeat)

1. Disconnect MAF sensor first. If the car runs exactly as it does with the sensor plugged in, then your MAF sensor is fine. If it runs better when its disconnected, then its Knackered, replace immediatley with genuine replacement part (do not use NON OE Sensors) these are more trouble than they are worth.
2. Check the EGR (Exhaust Gas recirculation) Valve. They can get clogged up with Crud and the flap can stick, causing wierd performance qualities. Poor acceleration,poor MPG etc.
3. Diesels take ages to warm up....... No point in taking any MPG readings until 10 minutes + on the road. 45 MPG on an avant aint that bad mate. Max you will see will be high 40's... IMHO

Out of interest, :-
A - How long have you had the car?
B - Has it always made those MPG figs?
C - When was the car last serviced?
D - Mileage?

Again as others have suggested, get yourself down to someone with VCDS (formely known as VAGCOM). You will possible save yourself a load of time and avoid changing or messing with something on your pride and joy that is actually working 100%.

If you are in Cheshire or nearby, PM me and I will plug in and have a look.

Good Luck

Blair
 

paul20v

Audi fanatic
Clough103,

A couple of things to try, breezing thru the thread briefly, others have suggested I see... (sorry to repeat)

1. Disconnect MAF sensor first. If the car runs exactly as it does with the sensor plugged in, then your MAF sensor is fine. If it runs better when its disconnected, then its Knackered, replace immediatley with genuine replacement part (do not use NON OE Sensors)
Not being funny here but if you had read the thread you would see that i have already said that if you disconnect the air mass meter that the car goes into limp mode this wont help
yes some cars will run tidy on base setting with the air mass disconnected but the 1.9TDi PD wont .
 
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