Maf sensor problems.

19 Mar 2015 | Author: | Comments Off on Maf sensor problems.



The info relates to BMW engines but also to many diesels including Vauxhall, Saab, Fiat, etc.

If your BMW engined suffers from poor below 1800-2200rpm it is most due to an out of spec maf sensor.

This can from as low as 30k miles.

The MAF sensor is in the inlet duct on the outlet of the air and measures the mass of air flowing the engine. In theory, therefore, the ecu can the correct amount of fuel for the air going in and thereby meet the emission regulations. Its located on the just behind and to the right of the oil cap. the connector is obscured by the top of the air filter housing lid. maf sensor info here )

In the Bosch sensor is notoriously and drifts out of spec as it ages. is understandable, since the sensor operates at 200 o C and semiconductors deteriorate at temperatures, even though seem to have overlooked fact!

The result is that the ecu commonly receives a reduced and because it cannot know if the is reduced from say a clogged air it must assume it is correct.

MAF sensor degradation NEVER up on standard diagnostic tests means your dealer NOT SPOT IT! (dealers rely too on fault code readers)

Maf failure – where it is or open circuit will up and will also light the management light on the dash.)

The maf has most impact below In the 1000-1700rpm range, where the is not generating much boost so there isn’t a surplus of it is difficult to meet emission without accurately metering the air so the maf signal can have a very effect on the performance.

Above 18000rpm, the turbo starts to effective and above 2500rpm is often a surplus of air and so the ecu does not to rely upon the maf signal as much. It can simply be programmed to the maximum amount of fuel and control the torque.

So if the maf signal has due to a degraded sensor, the first and obvious sign is very acceleration when pulling from rest. This stopping delay pulling roundabouts and into heavy is downright dangerous.

It also the car tedious and unpleasant to drive at below 2000rpm because the sudden fall off of torque more gear changing and the automatic models are just as some even stalling you pull away.

You will often find that torque occurs at much rpm than intended. Possibly not 2500rpm, whereas on the 75 ZT it should be 2000rpm, and on the Freelander, around (thanks to its variable nozzle

In about 25% of cases, the signal elevated above normal and will overfuel the engine at low Because this doesn’t in poor performance, it is all too easy to the maf is working okay. Very mpg, exhaust smoke, reeking of diesel when are tell tales of an overfuelling

So to sum up . the maf signal must be correct for performance AND economy. You can’t stick in any old maf, a cheap clone or ones sold for BMW and expect to get a good result. no tuning product – chip or remap will properly if your maf sensor is out of so if you are disappointed, after having Ј100s on such a product, to your maf sensor.

Many have sold their joy because they were of the poor performance when a 2 will cure the problem and performance to uptodate levels.

TIP. Save yourself a and sort a maf problem out yourself. I regularly from owners who been charged upto by incompetent garages who could not a weak maf and replaced just everything else.

NB: DO NOT FIT PIERBURGH MAF 09.0 with or without a 2 as this ONLY for BMW vehicles .


of the following scenarios best your car?

1) UNDERFUELLING MAF . maf signal from a … maf not open circuit) will fuel the engine to such an that it will NOT START. If you believe me, remove the maf from its reconnect it and try to start the engine. No = no maf signal = no fuel.

Very throttle response with slow initial rise in revs

Performance below is poor / has recently got worse and the can’t be felt until 2200rpm if at all.

I have to rev up and the clutch to pull onto roundabouts or there is a heart-stopping before it picks-up.

When I the throttle below about initially there is a moderate but most of the remaining travel is not to have any effect.

As the revs 2000-2300 the power starts to in suddenly and quite strongly in to lower rpm. (all or effect)

The engine is very to rev over 3000rpm even in gear.

If I unplug the maf connector, the low torque is much better, at higher revs it may be worse.

My 50-70 time in top gear is over what it should be.

I am with the results of having a box fitted, especially below

Fuel consumption has fallen

My auto stalls easily pulling away.

RECOMMENDATION: Fit A 2a or e but be prepared to fit a Pierburgh maf as well sooner or later.

2) OVERFUELLING A very high maf signal a faulty maf or short circuit to 5v overfuel the engine to such an that it will stall as as you touch the accelerator.*

Performance 2000rpm very good the car is very flexible and responsive

consumption is poor or appalling

I open the throttle, there is a then a puff of smoke and the car accelerates.

The exhaust smells of when idling

Idling is or uneven and fluctuates up and down and it

If I unplug the maf connector, the performance is the same or a bit worse.

*In extreme as soon as I touch the accelerator the chokes and stalls, with a of black/grey smoke smelling of


RECOMMENDATION: Fit a PIERBURGH MAF RonBox 2a or e must change the maf sensor as – a RonBox 2 will the symptoms caused by an overfuelling maf

3) MAF OKAY-ish

Performance below is the same as ever

Fuel is normal

I can just about the turbo from around

My 50-70 in top time is about seconds, (75/ZT)

However, the doesn’t really want to rev 3500rpm except in 1st gear. on a 75/ZT cdt)

I want better overall performance below 1500rpm to over

RECOMMENDATION: FIT A RonBox 2a or e. Expect to to fit a Pierburgh maf in due course if the performance and drops off.

NB: DO NOT FIT PIERBURGH MAF 09.0 with or without a 2 as this ONLY for BMW vehicles .

Fi a new Bosch maf and /or RonBox 2 + Pierburgh maf and the is still not right?

Here are other possibilities. (more here )

Lack of performance The RonBox has been proven of time to work as claimed so if you do not get the result as all our other customers will almost certainly be due to issue with the vehicle:

· / leaking or clogged egr valve remove and clean, refit but vacuum pipe off (the braided rubber tube)

· turbo or intercooler hoses or also internal delamination can often causing a brickwall rev

· Sticking wastegate or faulty (75/ZT) The linkage has been to come apart, leaving the open.

· FREELANDER ONLY: turbo vnt mechanism, faulty or solenoid, leaking vacuum If the vnt mechanism has jammed, the performance be poor at low rpm (but no smoke as pressure is low) if its stuck in the rpm setting, or vice versa.

· injectors or worn nozzles. If the cannot flow the extra you will not see any increase in performance. In should be considered a service once they’ve done 100k miles.

· Clogged These have been to collapse or disintegrate and therefore back pressure that the performance. Hard to diagnose

· Faulty fuel rail TD4 more prone due to water in the loom – see LR Tech 00052. Very common on the Td4, less so on the 75/ZT.

· A crankcase ventilation valve valve) can also affect the causing smoke due to too much crankcase fumes being it. A filterless cyclone type is from BMW, part no. and costs Ј27.50 inc VAT


I did some of a … maf kindly donated by an my good maf and a Pierburgh Maf.

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