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Bosch MAF Sensor Technical Paper

This downloadable PDF document is Bosch’s technical publication on the mass airflow sensor used in many front wheel drive Volvos.

Bosch MAF Sensor Technical Paper

This downloadable PDF document is Bosch’s technical publication on the mass airflow sensor used in many front wheel drive Volvos.

– Measurement of air mass (gas mass) throughflow per unit of time, independent of density and temperature. 

– Extensive measuring range. 

– Highly sensitive, particularly for small changes in flow rate. 

– Wear-free since there are no moving parts. 

– Insensitive to dirt and contamination

Application
Measurement of air-mass flow rate to provide data needed for clean combustion. Air-mass meters are suitable for use with other gaseous mediums.

Design and function
The sensor element comprises a ceramic substrate containing the following thick-film resistors which have been applied using silk-screen printing techniques: Air-temperature-sensor resistor R?, heater resistor RH, sensor resistor RS, and trimmer resistor R1. 

Installation instructions
Water and other liquids must not collect in the measurement venturi. The measurement venturi must therefore be inclined by at least 5° relative to the horizontal. Since care must be taken that the intake air is free of dust, it is imperative that an air filter is fitted.

Bosch MAF Sensor Technical Paper:
Check out the Full PDF Here…

frootmig » I have a 1995 Volvo 850 2.0 20V Automatic, the car appears to be between a 95 and 96 model as it has an OBDII connector, but I had to make a little LED and switch combo to read the usual flash codes, found the info on this excellent site.

The car has recently had a full service, new plugs, air filter, oil etc…

The problem started while we were on holiday with the engine intermittantly cutting out, I called the RAC out, after looking at the codes (it was 1-2-1, showing a MAF error) we unplugged the MAF sensor and the engine ran without any problem, other than poor idle (I put this down to the MAF being unplugged), we drove the car home (Over 270 miles) without any recurrence of the cutting out problem, the fule consumption was almost the same as it had been before the problem.

When I got home I ordered a new MAF sensor (Not a Bosh original) and fitted it when it arrived.

I cleared the codes and started the engine, the engine started well and appeared to idle quite well, I then moved the car into D the engine almost stalled. I thought it may be the PND switch so I moved the shifter back and forth several times but it did not help.

Next I tried to rev the engine, firstly it hesitates on initial acceleration, but if I open the throttle wide open the revs will hunt with the revs going up to about 4000 and then cutting out and dropping to about 3000, if I close the throttle a bit the revs will stabilise, if I open the throttle slowly the revs will happily go past 4000. I have looked at the vacuum hoses and found one with the rubber connector perrished, I have replaced that, but the problem still exists. I thought it was originally the new MAF that was faulty so I sent it back, but the replacement gives exactly the same problem.

I have removed the IAC valve and used the diganostic tests built into the ECU to test it, with the IAC closed it is still allowing some air to pass when I blow through it, should the IAC valve seal completely when closed?

If I unplug the MAF the engine revs freely to 7000 rpm without any problems and drives quite well (lacking a bit of performance) so I think it rule out any problems with the ignition and fuel systems.

I think the problem with the revs hunting when the throttle is quite wide open must be due to a leak in the intake system, but I am not sure where to look now.

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1 Comment

With the engine at idle, the MAF’s PID value should read anywhere from 2 to 7 grams/second (g/s) at idle and rise to between 15 to 25 g/s at 2500 rpm, depending on engine size.

In modern cars, the only way to test the mass air flow sensor is with a scan tool. Mechanics measure the amount of air flow (mass air flow sensor readings) at different RPMs. They compare the readings to the specifications or to the readings of a known-good mass airflow sensor.

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