PERFORMANCE AND ECONOMY KILLERS

HOME       ROVER 25/45/MG ZR /ZS MAF ISSUES      ROVER75 MG ZT, FREELANDER TD4 MAF ISSUES              

INTRODUCTION.

The maf or air mass meter or airflow meter is the biggest cause of poor performance and economy on modern diesel engines (mainly those built after 1999).

Unfortunately, they are not a reliable component and this means that as many as 50% of diesel vehicles on our roads could have an out of spec maf sensor to the detriment of economy, performance and emissions, which is ironic because its an important component in emissions control!!.

There are three main symptoms of an out of spec maf:

1) poor performance especially below 2000rpm

2) an unexplained rise in fuel consumption.

3) flat spots, hesitation, juddering, exhaust smoke, stalling.

To read how the maf sensor had a drastic effect on a Rover 45 diesel & how we cured it click here and for more on how it affects the Rover 75, MG ZT,  Freelander Td4 and BMW engines click here.

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.

WHEN TO REPLACE THE MAF SENSOR?

In most cases it is beneficial to performance and more importantly, to economy, to replace the maf every 50k miles or 4years. In fact it is not really the mileage that is important, but the total number of hours the engine has been running. This is because the maf employs a heated element, operating at up to 200C and at this temperature, the sensor element and electronics will degrade steadily, affecting both the sensitivity and linearity. So a low mileage vehicle used for short slow commuting type journeys may actually have been running for the same number of hours as a newer one used for high motorway miles.

TO SUM UP:

If your vehicle's performance below 2000rpm has become sluggish or fuel consumption is worse than it used to be, seriously consider replacing the maf sensor.

MORE ON MAFS & MAFAMS HERE

MAF SENSORS & MAFAMS ARE AVAILABLE TO BUY ONLINE FROM OUR SISTER COMPANY ENERGY TUNING LTD HERE. 

 We now stock maf sensors for popular diesels known to suffer from the effects of an out of spec sensor.

We only supply branded sensors - eg Pierburgh, Hella etc

With the exception of the Rover and BMW engines, nothing else is needed - the maf will be a direct replacement for the original. In most cases it will be identical in make and part number to the original.

Available for:

PIERBURGH:

MERCEDES 200, 220, 270, 320, 400CDI  in cars and commercials from 1999 onwards

FIAT 1.9TD, 2.4TD / SAAB 2.2TiD,  VAUXHALL  2L, 2.2L DTI

HELLA: PEUGEOT / CITROEN HDI 90/110 in all cars and commercials from '99/00

FORD / PEUGEOT / CITROEN 1.4 TDCi/HDI

FORD / JAGUAR XTYPE 2L 130/128 TDCI/DCI

FORD 1.8TDDI, 1.8TDCI