Does this look like a normal MAF chart?

[rasputin]

We have a BMW 120i that I suspect has a faulty MAF.

I plugged in an OBD2 thingy and this is the Mass Air Flow Rate at idle with a warm engine:

[Superhoop]

I'd say not.

At idle, with no other inputs from throttle etc, MAF should be relatively stable, with very little rate of change.

[buggalugs]

The scale looks a bit deceptive there.

I have never actually seen a graph of MAF readings on a warm 120i though so not sure I can say really.

[rasputin]

You're right... The scale is quite deceptive. It only actually "jumps" between 3 and 4.

When I floor the throttle I think it goes up to 80+

Having a lot of trouble finding another car that allows a generic OBD reader to see MAF values though!

[kambites]

I can have a look at the Lotus this evening and see what variation I get, if you like.

[rasputin]

That would be really helpful

[mini me]

What are the units?

[rasputin]

I think it shows grams per second or something like that. Not completely sure...

[mini me]

rasputin said:

I think it shows grams per second or something like that. Not completely sure...

If that's the case then I would imagine the signal is pretty normal. Just checked a trace from an engine I'm working on at present and I can see roughly the same signal shape albeit at a higher rate as I'm doing diesel. I can see about 3kg/hr variation which equates to roughly the same you are seeing/sec. Can't say if the mean amount is high or low though. I only do dirty dervs.