E90 MAF Issue

DublinDilbert

Hi All,

Background:-
E90 320i 2006, experience a slight roughness at idle and sometimes sluggish at low RPM. No DTCs set in DME, checked with INPA & OBDII reader. Fuel trims all look normal. Passed NCT emissions test with flying colours 2 weeks ago.

Had a look yesterday, here's what i found:-
1) No Mass flow value showing up on INPA live data,air intake temp ok
2) No Mass flow value showing up OBD2 reader live data
3) Checked Mass flow value read 0V (20mV) with multi meter
4) Checked 12V, 5V and Ground connections, all good
4) Unplug MAF, now get error code for temperature sensor out of range.
5) Plug MAF back in, can clear error for temp sensor, no other errors.

So it looks like a faulty MAF, cause i assume i should at least get 1V back with engine not turning over. Which should rise up towards 4.5V at WOT.

What i can't understand:-
The car seems to be running a little too well for no MAF value. I know the DME can estimate this, but didn't think it would run so well.
I don't know why no DTC is being set for a MAF value of 0V coming back in.

Nissan doctor

What engine is it?

If there was a MAF issue there would certainly be faults recorded. No idea why your not getting a value but if the MAF was giving the ECU no reading then there would be codes stored.

Is the rough running only at idle with all other revs/driving perfect?
If so I'd be checking that the oil cap is fitted correctly and then checking the breather pipes to/from the oil separator.

DublinDilbert

Nissan doctor wrote: »

What engine is it?

If there was a MAF issue there would certainly be faults recorded. No idea why your not getting a value but if the MAF was giving the ECU no reading then there would be codes stored.

Is the rough running only at idle with all other revs/driving perfect?
If so I'd be checking that the oil cap is fitted correctly and then checking the breather pipes to/from the oil separator.

Thanks for the reply, yep its the N46 engine. Its idling rough and some times is quite sluggish in the lower RPM range.

Yea i did suspect a vac leak from one of the seperator pipes or the oil seperator itself. There is a vacuum in the crank case, when i try remove the oil cap, but its not excessive. I'll have to get under the manafold to have look at it.

The think with the MAF reading zero is really thrown me, cause i've replaced a MAF on an 07 E90 before and it was definitely throwing codes in the DME and running like crap.

I thought even if there was a "major" vacuum leak that there would be some voltage from the MAF, I thought these give 0.5V with zero flow.

I'll have another look at it this morning...

AzureAuto

Check with ignition at position II at the reference signal wire of the MAF connector (MAF unplugged) for 5V. Then plug it back in and with engine ticking over this value should be around 0-5V because of the voltage drop across the circuit, i.e. the reason you are getting 0V is because the circuit is fine. This voltage will rise incrementally with RPM until close to 5V at WOT. If you also have battery voltage going to heat the hot film element then id say the MAF is working fine.
It would be odd for this component to fail and not log some kind of fault code...

DublinDilbert

Hi thanks, The reference wire is giving a solid 5v when just ignition on and also with engine running. The maf output line is sitting at zero volts at all time engine running or not, never changes.

When I unplug the MAF I get a maf temperature sensor fault, but no fault set for the main flow signal.

It's strange cause even an e46 will set a code if the MAF is signal faulty. There's defo something strange to see 0v, thought these give 0.5v no flow and 0.75v at idle.

Im wondering If there was a massive vac leak at the separator I guess there might be very little flow over the sensor.

crosshair1

You should certainly have a voltage there even if the is no flow over the sensor.
Can you supply a small voltage say 1.5v to the signal wire and see that the ecu accepts the input. That will confirm that at least the circuit and ecu are ok.
I think most will agree that Maf faults rarely will case a fault code.
Its not a digital maf??

Curry Addict

try a tap test on your MAF with the engine at idle speed, gently tap the MAF sensor with the fingers of an open hand, if the engine stumbles or stalls, the MAF sensor is defective.

DublinDilbert

crosshair1 wrote: »

You should certainly have a voltage there even if the is no flow over the sensor.
Can you supply a small voltage say 1.5v to the signal wire and see that the ecu accepts the input. That will confirm that at least the circuit and ecu are ok.
I think most will agree that Maf faults rarely will case a fault code.
Its not a digital maf??

Yea going to try this either this evening or the weekend. I'll stick a pot on the wire to the ECU and make sure I can see a value come in on the scan tools. If i didn't know any better i would guess someone has been messing with the ECU in this car or something. I don't think its possible to code it out, but who knows what some people will try and do. Will get to the bottom of it one way or the other :-)

crosshair1

Just had a look at wiring diags for this and it appears there is a version that
doesnt have a maf input.
Whether the maf is still fitted or is a dummy with only the iat I dont know..
See link, autodata also lists 2 possibilities.
http://wds.spaghetticoder.org/en/svg/sp/SP0000026310.svg?m=e8790

or.. maybe your ecu/software is incorrect

DublinDilbert

Hi All,

Finally had a look at this again. I attached a POT onto the MAF connector and I can now see a flow value on both my scan tools. I can turn the pot up/down and the flow value changes as I would expect. So it looks like the MAF is dead, anyone know where is good to pick up these bosch parts or are all motor factors much the same? eg €200?


What I still don't get is why no DTC is being set, also when i was adjusting the POT up/down I wasn't seeing any changes in engine speed / fueling, although i guess if its used to running without MAF the adaptions have been modified for this. In Saying this the fuel trim values look fairly normal and it passed the NCT emissions test 4 weeks ago.

DublinDilbert

Ok, just checked real oem again with the exact VIN:-
http://www.realoem.com/bmw/showparts.do?model=VA52&mospid=48822&btnr=13_1146&hg=13&fg=20

For this model it lists a MAF or a temperature sensor:-

07 Pipe, temperature sensor 1 13627533853

For vehicles with
National version Korea
or
National version China
or
Equipment for leaded fuel
or
Low compression engine
L802A=Yes
L8AAA=Yes
S199A=Yes
S858A=Yes

07 Hot-film air mass meter 1 13627566989

So it looks like there possibly is no MAF, hence no MAF issue :eek: