THE TUNING-DIESELS GUIDE TO MAFS
a) HOW DOES THE MAF WORK?
The MAF or Mass Air Flow sensor (also known as air mass meter or airflow sensor) relies upon the principle of the cooling effect of moving air (think ' windchill') past an element heated to 200C.
Most of them are not very reliable after as little as 30k miles. If they just worked or didn't. it would be easier to diagnose a faulty one. But they don't -they can become less sensitive over time or can change sensitivity suddenly for no apparent reason. Some will output too high a signal, causing over fuelling, smoke from the exhaust and poor fuel consumption, but usually the signal drops giving very sluggish performance below 2000rpm and delaying the build up of turbo boost.
How not to spend £100s on an expensive tuning box or remap or Maf sensor.
Many many owners, unaware of the effect of an out of spec maf, have spent as much as £500^ or more on an expensive tuning box or remap to boost poor low down performance. Others have been very disappointed with the results given by a remap or tuning box. ^ I was one of them until I discovered the effect of the maf and then developed the Mafams.
IN BOTH CASES THE MAF SENSOR IS TO BLAME.
Before spending £100s on these products, please check that your maf sensor is working.
b) HOW TO CHECK FOR MAF SENSOR DETERIORATION
Simply unplug the connector from the sensor (with the ignition switched off). This will cause the ecu to use its backup values which usually results in a noticeable performance improvement at low rpm but possibly worse performance above about 3000 to 3500rpm if your sensor is defective.
Do not leave the sensor unconnected for long because on some models it may cause the MIL (malfunction indicator light, engine warning light) to illuminate. This will normally go off once the maf is reconnected though it may take several engine starts before this happens. Also, without the maf connected, the overrun fuel cut off, egr system, IAT and timing will not be optimum and fuel consumption will be worse. So regard disconnection as a stop gap measure for a few days.
There is more info on my website. Tuning-diesels.com
Q1: WHICH ENGINES ARE AFFECTED BY MAF FAULTS?
A: Almost ALL modern diesel engines from about 1999 are fitted with a maf sensor which influences the fuelling. Prior to 1999, the maf was only used to control the exhaust gas recirculation system and does not have much impact on fuelling.
Q2: MY DEALER CAN'T FIND ANYTHING WRONG
A: An out of spec maf sensor does not cause a fault code to be logged. Some manufacturers' dedicated diagnostic equipment can be used to check the maf sensor at a fixed rpm - often 3000rpm, but this is not a definitive test. The sensor maybe be fine at 3000rpm on no load, but useless from 1000-2000rpm on the road.
Q3: WHAT ARE THE SYMPTOMS OF A FAULTY MAF & HOW CAN I TELL IF IT IS FAULTY?
A1: Loss of power throughout the rev range, can indicate a dead maf (possibly even worse at low rpm).
A2: Loss of or absence of low down power (below about 2000 to 2500rpm - i.e. before the turbo comes in) Turbo comes in at much higher revs than it used to.
A3 : Not too bad low down, but a reluctance to rev.
A4: No loss of low down torque, but smokey, smelly exhaust, possible stalling with clouds of smoke as soon as the throttle is opened, hesitation & smoke when starting to accelerate, very poor mpg.
Q4: DOES CLEANING THE MAF HELP?
A: It is worth trying but any improvement is usually temporary , also clean the electrical contacts. BE VERY GENTLE.
Q5: IS THERE A CHEAPER ALTERNATIVE TO THE EXPENSIVE OEM MAF?
A: A Pierburgh maf works well and costs £53 from my online shop. BUT it must be used with a Mafam. The Pierburgh + mafam combination is suitable for the Rover 25/45/Zr/Zs/75/ZT/Freelander Td4, Frontera/ BMW diesels etc
c) THE MAFAM
The mafam compensates for maf sensor deterioration by boosting its signal, restoring lost torque and enabling the turbo boost to build sooner. It connects between the maf sensor and its plug and requires no wiring mods so is reversible and transferable to other vehicles.
Q6: WILL FITTING A MAFAM CAUSE MOT SMOKE TEST FAILURE OR DAMAGE MY ENGINE?
A: NO. Even with a Superchip remap, boost turned up, no cat and a Mafam, my previous 45 passed the MOT first time. A mafam cannot damage your engine any more than an out of spec maf can.
Q7 FITTING A MAFAM WILL SURELY AFFECT THE EMISSIONS?
A: Driving around with an out of spec maf sensor certainly will. If you consider just how many diesel vehicles have maf sensors that are out of spec, this single component must be responsible for at least 10% of the CO2 emitted by diesels. Fitting a mafam usually results in improved mpg and this means less CO2!
d) MY RECOMMENDATIONS.
- Fit a Mafam first. If this restores lost performance then this is all you need.
- If performance is still lacking or uneven or the engine won't rev, then change the maf as well.
- If you drive a Rover 75, MG ZT, BMW 320/520 or Freelander TD4, my Synergy module combines a digital version of the mafam and a Tu3 tuning module in one compact unit. It both boost performance and compensates for any maf deterioration for less than the cost of other companies bog standard tuning box..
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