Afternoon all, Been reading a few threads on here about unplugging MAF to see if car runs any better to test if the MAF is naff.

 

Everyone seesm to be saying there car runs alot better with it unplugged. Assuming this means there MAF is knackered.

 

When I unplug mine, It runs like dog ****. Its like I have unplugged the turbo. No spool up, No Power, No lights....Does anyone know whatthis means? 

 

Cheers All

 

LeezoG

Edited 1 December, 201411 yr by LeezoG

I would guess that with the maf unplugged the ecu has to make an assumption on worse conditions. I.e. low air flow at higher temperature, so the smoke map limits the amount of fuel.

At this time of year with the cold air temperature is more dense so technically the engine will be running slightly lean.

The vrs has a map and a maf but as far as i know only uses one of them which as standard is the maf, not sure if the maf is unplugged wether it will switch to using the map.

maybe faboka or sepulchrave could shed more light.

or more simply with it unplugged its registering a fault and going into limp mode.

Edited 1 December, 201411 yr by Richard-vrs

Cheers Rich, Yea I'm under the impression from what I read that when the maf is unplugged it switches to the ECU mapping. Mine reverts to a turd on wheels. But other peoples seem to work just fine....improved in some reports lol..Im no way a mechanic or mechanically minded im going from what I read from other people on the site

 

Also I should clarify....when i say "no power"...I mean the car drives, just no turbo. And "No lights" is no lights coming on on the dash

Edited 1 December, 201411 yr by LeezoG

That sounds more like limp mode, a fault can still register without showing a light on dash.

Im still not sure how peoples can run better with maf unplugged it shouldnt be possible, unless they are actually running off the map sensor.

The diesels engines have MAF and MAP sensors. BLT and SDI engines use the MAP sensor for the smoke maps the rest use the MAF sensor.

If you have a MAF based ecu limit fuel based on airflow past the MAF sensor. Unplugging it will result in a default MAF reading of 550mgstroke. This results in fuelling being limited to this column of the smoke map which in turn will reduce boost pressure. So unplugging it will not make it run better but worse.

MAP based ecu's limit fuel by boost pressure. Unplugging the MAF will not effect fuelling.

Both ecu's will throw a fault but neither will allow the car to run better.

I had a feeling you would know the values it reverts to when maf is unplugged john.

still not sure how people are getting a better running car when it is unplugged though.

I cannot see how this would work on a tdi other than stop the egr from operating. The ecu won't revert to any other map to continue to operate.

I'm currently running with MAF unplugged, cos I'm trying to find out what's wrong with car. Was told try with MAF unplugged, if it runs better or no worse then MAF is fubar. Car actually runs a lot better with MAF unplugged, go figure.

Are you saying unplugging MAF is having some other effect, like disabling EGR, and that is what's making car run smoother (because EGR is fubar)?

Edited 1 December, 201411 yr by vRSWitter

I think only proper way to find out would be to take some logs with and without maf plugged in.

Is yours asz or blt vrswitter?

I think only proper way to find out would be to take some logs with and without maf plugged in.

Is yours asz or blt vrswitter?

BLT

BLT runs of the MAP sensor. Download VCDS lite and buy a £10 third party cable of eBay. Then take logs of group 3.

BLT runs of the MAP sensor. Download VCDS lite and buy a £10 third party cable of eBay. Then take logs of group 3.

 

Got VCDS and cable, but lattop is old and temperamental (battery). Will try and get this logged at the weekend. Shame you're all the way up north because I'd gladly pay you £LOTS to sort this mess out. Been driving me mad for over a year now!

I'm currently running with MAF unplugged, cos I'm trying to find out what's wrong with car. Was told try with MAF unplugged, if it runs better or no worse then MAF is fubar. Car actually runs a lot better with MAF unplugged, go figure.

Are you saying unplugging MAF is having some other effect, like disabling EGR, and that is what's making car run smoother (because EGR is fubar)?

Starting to think I was going nuts.....Thanks dude lol

 

I got the ASZ Engine so does this work differently? Because when I unplug my MAF....Its like a direct plug to the turbo lol I'm getting seriously confused lol

The engine fuelling is limited by 3 maps in stages, the first is controlled by accel pedal when you put your foot down past a certain point, the ecu looks at the second map which is controlled by air flow. In the case of the asz it uses the maf to do this, as mentioned by faboka earlier by unplugging it the maf reads a constant value of 550.

This is basically restricting the amount of fuel alot, so even if you put your foot down the ecu will is limited to only inject the amount of fuel specified when the airflow is 550.

The turbo is controlled by how much fuel is being injected. So in basic form maf controls fuel which controls turbo.

Hope this helps but if you want more info check out faboka website http://www.hidden-power.co.uk/guides/bosch-edc15p/

Edited 2 December, 201411 yr by Richard-vrs

Yea makes sense really, Thanks to everyone for the replies. What a community!!

The blt engine uses the map sensor which measure the pressure of air out of the turbo, which is why when unplugging the maf doesnt make it run like crap.

However from what ive read the maf still controls the egr valve, from memory 550 isnt a high enough value to turn the egr off. So to see improved performance would suggest maybe sticky egr valve, might be worth giving it a clean and reconnecting maf to see what happens.

I can only assume that by coincidence everyone else who has unplugged the maf and seen improvement is also running the blt engine or some other variant which uses the map sensor instead of the maf.