What does the MAF Sensor do?

...and no clever dick one line answers like "senses the air flow"!

That much is obvious but what does it sense, the temperature, humidity, volume, pressure?

and

what does it then do/control with regard to the engine running?

A sick TD5 owner (rapidly becoming bankrupt) is very curious.

Thanks

You sort of answered your own question,it measures the mass of air being ingested by the engine.With this info,the engine ecu,(with the info from all the other sensors around the engine)decides what outputs to make.Mostly start and duration of injection of fuel into all 5 cylinders individually.But also control of the glow plugs,ie how much post start glow to apply to keep emissions down to an acceptable level.
The engine will run with the Maf unplugged,using default values - as a back up.Apart from the crank position sensor the td5 engine will run with most of the sensors unplugged - maybe not very well,and some of them will put the check engine lamp on aswell - but it will still go.
Is that enough info ?

How perfect is that!!!!

Thanks a bunch.

I suspect the garage replaced mine unecessarily in trying to sort out why it will not start without excessive cranking. They are a LR dealership and have had the car 3 weeks now!!!

Worst is they have confirmed they now think it is what I said it was 3 weeks ago. Somehow air is getting into the system and that requires drawing fuel back through the system before it starts. I suspect a hard to spot hairline crack somewhere. Unfortunately there are no signs of diesel leakage anywhere which would be a big help.

Its much more likely to be low fuel rail pressure than air in the fuel.Fuel pumps cause this most often - easy to check,just tee in a gauge at the back of the cylinder head and watch the fuel pressure whilst cranking.If the pressure is there then hook up an oscilliscope to the crank position sensor then the injector wires.These engines may be more complex than a Tdi but they are not rocket science,and diagnosing a fault like this is a straightforward process.

Laugh, try telling Landrover that. They replaced the fuel pump prior to the MAF. So now they think it is air in the system.

I spent all day going through the workshop manual and from what I can gather key potential hotspots, not in this order, seem to be;

AAP - Ambient Air Pressure sensor
MAP - Manifold Air Pressure sensor
ECT - Engine Coolant Sensor
FT - Fuel Temperature sensor
Glow Plugs

Any of the above can show symptons that I am suffering concerning starting. Yet all have default settings that the engine management will apply in event of a failure. Therefore the engine still runs once you get it started.

I dont know if the diagnostics system they use in workshops is clever enough to show the condition of individual sensors.

Testbook can give all the sensor outputs on a screen of live data,I really cant understand why they cant sort it,if there was air in the fuel the pressure would fluctuate as it passed through the system,I Tig welded a little tee pipe so I could connect up a Snap on oil pressure gauge to check Td5 fuel systems - the hose is long enough that I can tape the gauge to the door mirror so I can watch it whilst driving along.(Some Td5 fuel pumps play around before they die completely)

Ok by way of closure on this thread and after a long 8 months of hassle where Land Rover Switzerland failed, I shipped the car back to the UK into the hands of LR UK and hey presto, just got the following email;

Just had phone call from Hunters. Found oil in main injector loom & main harness, they've fitted new turbo hoses, looms & laminations. All 100% paid for by Land Rover & we have to collect tomorrow morning. She couldn't call you as she can't dial your number from her phone - uk only I suppose. So that's good news. By the way we asked the salesman ref price & he looked up trade price as being about £9995 so with luck you'll get more than £7,500.

Anyone want to buy a nice Land Rover? I got so ****ed off with it I bought a new one.