someone please please help

I'm still thinking it could be maf sensor I had an audi that ran like my td4 does at the moment and that turned out to be a faulty maf

I would agree - hands down....

Would it cause it to smoke so much though?

leeogt4 said:

Arctic2 Where is the map sensor located ?

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Right hand side of the engine on the side of the manifold, pics below, it could be the MAF but unplugging it you should see a difference, on the R75 a few members have found these aftermarket MAF's to be ok but I prefer the original bosch.
Couple of links below.
http://www.ebay.co.uk/itm/321779444446?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

Aftermarket maf
http://www.ebay.co.uk/itm/LAND-ROVE...4e49c20&pid=100005&rk=5&rkt=6&sd=321779444446

Claiming to be original if these are right then a great bargain, I would ask lots of questions though before purchase.
http://www.ebay.co.uk/itm/NEW-GENUI...ND-ROVER-FREELANDER-MG-ZT-20-TD-/171910507848

hd3 said:

td4 maf is pre-egr valve in the intake airflow system .. the maf sensor can't have a clue how much exhaust gas is being introduced via the egr valve
maf sensor voltage output .. determines how much fuel can be injected on go-pedal 'demand' without being over rich in mixture .. if maf be disconnected the ecu relies on an internal substitute maf mapping

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leeogt4 ..
make sure the egr valve .. if fitted .. is clean and doesn't stick ..
better still get rid of it altogether .. replace it with an egr delete/bypass unit
one thing less to go wrong and cause crap-engine-running issues ..
better mpg and go-pedal response without it ..

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On a diesel engine. Don't talk out of your arse.

Would it cause it to smoke so much though?

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maf's can degenerate / fail into 'overfueling' or 'underfueling'
latter is more common

td4 engine faults :
http://tuning-diesels.com/75Zt/R75faults.htm

about the 'maf' sensor :
http://tuning-diesels.com/75Zt/R75maf.htm

regarding the Air Intake Temperature sensor :
http://www.landyzone.co.uk/lz/f9/black-smoke-224520.html

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it wouldn't surprise me if the ecu 'default' maf mapping would be on the fuel-rich side ..
as similar to the air-temp-sensor defaulting to -5c temp if that sensor fails altogether
( a -5c air temp default reading would cause overfueling / smoke .. if the air intake temp.
( be actually much greater than the default data

Listen carefully i will say this only once. Diesel engines are throttled by fuel not by air. For any given engine speed, manifold pressure, there is always the same amount of air in the cylinder. The exception being if EGR is active. When EGR is active the reduction in airflow through the MAF sensor tells the ECU how much exhaust gas is being ingested. The ECU then modulates the EGR control valve to adjust the exhaust gas being ingested. The reduction in oxygenated air cools the combustion temperature to reduce Nox production. The fuel being injected does not change. Reducing fuel lowers the engine RPM increasing fuel raises engine RPM. Simple as that, the MAF sensor DOES NOT control fuelling on a diesel.

The exception being if EGR is active. When EGR is active the reduction in airflow through the MAF sensor tells the ECU how much exhaust gas is being ingested. The ECU then modulates the EGR control valve to adjust the exhaust gas being ingested. The reduction in oxygenated air cools the combustion temperature to reduce Nox production.

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not an 'exception' .. but an 'also'

Simple as that, the MAF sensor DOES NOT control fuelling on a diesel.

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it does at lower rpm

well .. that's according to rover ron .. :
"
WHY DOES THE MAF HAVE SUCH AN IMPACT?

The engine management system uses the maf sensor to measure the mass of air entering the engine. At low rpm when the turbo is not working efficiently and there isn't an abundance of air available, it is important for performance, emissions and fuel consumption that the air is accurately measured. If the maf signal is below par the fuelling is reduced and performance suffers, if it is too high, fuelling is increased leading to smoke, and poor mpg, as well as lumpy, hesitant, juddery running. In extreme cases stalling or bad starting can occur.

Above about 2000rpm on most car and van engines, the turbo is within its full operating range and there is a surplus of air available so the maf signal assumes less importance because the ecu can simply use predetermined fuel maps to control the torque. i.e the assumption is made that there is more than enough air available so it need not be measured accurately.

The egr valve...

The ecu also uses the maf signal to control the exhaust gas recirculation (egr) system. When exhaust gas is admitted it replaces inducted air so the maf signal drops. The ecu can therefore determine how far to open the egr valve. If the maf signal is unusually high, too much exhaust gas can be admitted or the egr valve does not close quickly enough or sufficiently when the throttle is opened. This causes hesitation and flat spots as well as performance issues.
"
" engine won't start - with no maf signal no fuel will be injected so the engine does not start. "
( above from: http://tuning-diesels.com/Mafam/mafhome.htm )

On early Td4's the MAF also has the inlet air temperature sensor built in. If this part starts to fail it can screw up the amount of fuel needed, and disconnecting the MAF/IAT sensor can make the ECU run on default settings.

The MAF actually does have a function on modern diesels and people don't understand why.

When the euro emissions rules started to come in they became very strict about particulate out of a diesel engine. Now, yes a diesel operates by volume of fuel injected and not the air fuel ratio that a petrol engine needs a MAF for.

The purpose of a MAF on a diesel is completely different - its not really for checking air fuel mixture to make sure the engine runs at the correct mixture like a petrol. It's to keep the particulate down - there's a point in every boost/rpm combination the engine is capable of where exceeding the fuelling doesn't add power; it just adds particulate.

The point of the MAF is to stop fuelling exceeding this point.

Old diesels like the L series didn't give a crap, they just blew smoke when you put the boot in and fuelled to excess because you didn't need to monitor the mix. The EU got wise to this and started the euro n rules.

The early stages of this were that the ecu had to monitor the mixture so that it didn't overfuel and blow particulate to an extreme. The next step was the diesel particulate filters to catch the little excesses that couldn't be programmed out.

This means that the modern diesel MAF is there to limit diesel injection - which means when it starts failing it causes unpredictable trouble because if its showing under reading the ecu will not inject fuel and if its showing over reading you'll blow masses of smoke out the back.

Edit; its not just the particulate, I was using that as an example - its also all the other harmful gasses that get created as well during over fuelling.

Ok so I've cleaned the maf sensor and the map sensor which was all clogged up with gunk and now it's pulling a lot better but still very smokey I did notice oil in the air intake pipes both sides of the maf so all cleaned out is there any oil breather pipes that could possibly blocked up on the engine? ?

The MAF does not control fuelling it controls the EGR. The fuel injected for any particular load/manifold pressure engine RPM is always the same. Only thing that changes is the amount of oxygenated air in the cylinder as EGR is functioning. Excess oxygenated air not required for combustion at the power level requested is replaced by inert exhaust gas to reduce the combustion temperature and reduce Nox emissions. If the MAF or EGR valve fail causing EGR to be actioned when it shouldn't be, soot is produced through rich mixture. The reason the MAF has a temp sensor in it is so the ECU knows the temp of the air going through the MAF. Hot air is less dense than cold air, If it did not know the temp the mass flow reading would be wrong. If the ECU does not know the flow rate through the MAF, exhaust gas ingestion cannot be measured accurately and the engine will not run correctly. This is EGR with feedback control as per EC level 2 standard. If either of the sensors in the MAF fail or send incorrect info to the ECU the ECU can become confused and misinterpret air conditions.

leeogt4 said:

Ok so I've cleaned the maf sensor and the map sensor which was all clogged up with gunk and now it's pulling a lot better but still very smokey I did notice oil in the air intake pipes both sides of the maf so all cleaned out is there any oil breather pipes that could possibly blocked up on the engine? ?

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Have you thought about cleaning out the intercooler? It being clogged up could be the reason for your smoke.

That's my next job I think wammers thanks for all your advice guys

Just one other thing not sure if this is normal or not if I have the engine running and take of the oil cap there seems to be a lot of pressure there could that be a sign of a blocked breather pipe or something? ??

Check all vacuum hoses especially the one that runs on top of the fuel rail with the shield on it.
Mine used to smoke heavily under load until I changed them.
It now picks up earlier and no smoke.
Interestingly I had to change the boost pressure sensor soon after.
Maybe it was the shock of all that extra suck.

As to your last post that sounds like the crankcase filter under the air filter has nether been changed.

It's got the bmw uprated crank case filter in fitted it a few weeks ago

Is the turbo spinning up

Yes the turbo spools up nicely