Really weird

[television]

I have had the MAF disconnected for 2 years on my V70R (saving for a new one) when it went in for the MOT I had to reconnect otherwise it was 3 times over the limit on the Co2.

Driving the car over a fast 200 mile run to the airport with the MAF disconnected it returned 34 mpg, with the MAF connected it never does more than 24 mpg at the speeds that I did, well over the 80's for most of it.

Am I missing something here

 

[Cole@MBS]

I have had the MAF disconnected for 2 years on my V70R (saving for a new one) when it went in for the MOT I had to reconnect otherwise it was 3 times over the limit on the Co2.

Driving the car over a fast 200 mile run to the airport with the MAF disconnected it returned 34 mpg, with the MAF connected it never does more than 24 mpg at the speeds that I did, well over the 80's for most of it.

Am I missing something here

Now that dont add up!!!

 

[television]

Now that dont add up!!!

Its true and still showing 33.7 mpg,, its best average was 25.7 when it lived in Herts.

It does 20 around here on service work

 

[Xtractorfan]

I know of many garage men who disconnect or even cut a few wires to the MAF and the cars run fine without them..mainly petrols I would add

 

[television]

I know of many garage men who disconnect or even cut a few wires to the MAF and the cars run fine without them..mainly petrols I would add

I have lost some acceleration, its slightly delayed (turbo) but not much, this is why I have not bothered to replace it

 

[Dosco]

I have lost some acceleration, its slightly delayed (turbo) but not much, this is why I have not bothered to replace it

Then I wouldn't just remember to connect it before its next MOT - unless of course 'the milky bar kid' brings in a law to start checking cars by the roadside - "just on my way to the garage to have it fixed" is the answer to that one

 

[television]

Then I wouldn't just remember to connect it before its next MOT - unless of course 'the milky bar kid' brings in a law to start checking cars by the roadside - "just on my way to the garage to have it fixed" is the answer to that one

It has got me thinking that I could switch the thing in and out as I needed it, with the old one it will just stall when pulling away

 

[Alex M Grieve]

unless of course 'the milky bar kid' brings in a law to start checking cars by the roadside

I remember when MAFF had a whole Government Department all of its own!

 

[turbopete]

I remember when MAFF had a whole Government Department all of its own!

it still does! its called the "piggybank for all the money we robbed off drivers through extortionate taxes on fuel and road tax" nowadays! :lol::lol:

 

[Number_Cruncher]

>>Am I missing something here

Once you're at cruise, the fuelling will be driven towards lambda=1 by the closed loop controller.

One of the things the ECU does with the signals from the MAF is to calculate engine load. This is used to alter fuelling *and* timing. Without MAF, the timing will, perhaps, be set more advanced, and when you are running fast, the signal from the MAF will result in retarded timing, and hence, poorer economy.

As you haven't blown any holes in your piston tops, it looks like you're getting away with it!

In typical engine management practice, to obtain engine load, you either need air flow sensing in the tradition of K, L, jetronic and their more modern descendants after LH jetronic which use a MAF, or the other way to obtain a load signal is via a measurement of manifold absolute pressure, like D jetronic and descendants.

That a MAF can also provide some estimate of the mass of air going into a particular cyclinder to help with fuel calibration is a bit of a nicety in comparison with its function as a load indicator.

 

[Xtractorfan]

Whilst no one can disagree with the above analysis, the purpose of the MAF is to monitor and indeed feed the required parameters for a fully efficient engine, but for the MAF to work the engine must have a default or factory setting that enables that engine to run at its most efficient.. So basically removing or disconnecting the MAF will allow the engine to return to its original or default settings....

 

[Number_Cruncher]

>>but for the MAF to work the engine must have a default or factory setting that enables that engine to run at its most efficient.

I'm not sure about that - it would be interesting to find out what air flow and air temperature the ECU assumes when it detects the MAF has been disconnected.

 

[Xtractorfan]

I'm led to believe that the ECU will only recognise the MAF when it is in circuit, and take readings accordinly, apparently if it is disconnected then the ECU like maneul Knows nothing..

 

[Number_Cruncher]

>>apparently if it is disconnected then the ECU like maneul Knows nothing..

That's interesting. It's fairly common that after a sensor failure, the ECU assumes something fairly safe and sensible, and drops into a reduced performance mode with the engine management light lit - however, I can well imagine MAF being completely ignored since with a combination of known engine speed and known throttle position, the ECU should have a reasonable idea of what the engine load actually is, and the lambda sensor will continue to nudge the system back towards stiochiometric.

 

[Cnics]

It's funny isn't it, moving on from the MAF, We get 25% better economy without the EGR valve on both the sprinters and transits i'm using with a company. First came to my head when i absolutely hammered a 316 from home to Weymouth, foot on the floor wherever possible, through the night. between 100 and 105 all the way and brought back 29mpg. On the way home at 70-80 it did 23mpg. EGR valve is bypassed on full throttle.

I have no idea how this relates to the fuelling and economy, i only have a loose idea of what it really does and why it does it, but it DOES make a difference. On a number of vehicles.

All these things, do they make the engines run better? Last longer? More efficient?

Or do they make them last a shorter time, less reliable? run worse, less efficient but a bit cleaner out the back end? Or maybe not even that.