What does the MAF do?

[stu1]

I know it's supposed to tell the DME how much air is going through; but today I disconnected mine (so I'd know how it felt if it broke) then went for a drive and I really couldn't tell any difference at all?!?

Is this normal? If you disconnect the MAF does it just drive like it normally does?

Confused,
Stu.

[bahnstormer]

the maf is used to
make
apple
flapjacks
=]

sorry can't help ya =]

[George Davis]

Modern electronic engine management systems have some redundancy built in, so they can run ok with a bad sensor or two. MAFs measure air flow directly, but with other inputs the brain can figure out air flow close enough to do the job. RPMs and manifold absolute pressure and/or throttle position can be used to estimate air flow, and the O2 sensor is used to trim it. Plus it's probably stored a look-up table it can use if it's missing an input. At least that's how it worked in a 1996 Mustang I had.

[Javier]

Javier

[JAlfredPrufrock]

Mass Airflow Sensor... if I were you I'd probably disconnect the negative terminal on the battery for an hour or two today and then reconnect the MAF to avoid any issues that may arise.

[stu1]

No, no CEL. I guess what I was asking is does anybody else with an M50 notice any difference with the MAF disconnected?

[Javier]

learned about the air density in the area you normally drive, and is using that memory to handle air mass parameters. You will probably notice something going wrong taking the car to another area (High mountain roads for example), were the air density will differ.

Wonder why aren't you getting a CEL warning (guess you have one, I don't). Have never tried to unplug my equivalent device though.

Javier

[stu1]

So, if I unplug the MAF and then disconnect the battery for an hour...

As for the CEL, I've never seen it light in my car (and I would have thought it should have lit when the MAF is disconnected) - maybe it isn't fitted; I've never had the instrument cluster apart to find out. It not being fitted would explain why I've never had any luck getting a stomp test going.

Oh well.

[Dan in NZ]

Could be that the CEL bulb is burnt out... Shouldn't it come on briefly every time you start the car? I wouldn't know, I don't have a CEL.

[Javier]

Javier

[stu1]

Yep, Scotland.

[t_marat]

So what happened in the end? Your MAF turned out to be faulty?

[Jon K]

The CEL shoudl 100% come on when maf is disconnected.


There are a couple of wrong things in this thread.

A MAF sensor is COMPLETELY required on any electronic fuel injection car unless it has a MAP sensor (which ours by default do not). Throttle position sensor only tells the ECU to run open loop or not... when you floor the TPS opens and tells the ECU to switch to a FULL THROTTLE fuel map. The maf has a wire going thru it that gets real hot due to voltage, the air going across it cools it, that in turn tells the ECU how much air is going over it. If you unplug your MAF and have no CEL something is wrong.

[t_marat]

my car seems to have no CEL light

[shogun]

If you do not have a car according to US specification, your car has no CEL light. That was a requirement for environmental regulations in the USA.

[t_marat]

Will try disconnecting the MAF today.

Shogun and JonK, frankly don't know how to thank you for all your help. You really seem to have no selfishness :)

[Jon K]

that's what we do!