Discussion
My car (1999 E36 M3) has been below par for a while. Slightly lumpy idle, lacking power etc. thought it might be the MAF so ran some cleaner past it.
It's been really lumpy in the past week and using more fuel, no real 'fizz' in the acceleration etc.
Now, there are no fault codes but I did think it might be the VANOS unit as there is no 'kick' at the relevant revs anymore.
However, I tried unplugging the MAF for my journey today and the car seemed to run better, less lumpiness, better power and less fuel used.
Would MAF be a fair conclusion? And should it be at full power without the MAF, or a bit restricted?
It's been really lumpy in the past week and using more fuel, no real 'fizz' in the acceleration etc.
Now, there are no fault codes but I did think it might be the VANOS unit as there is no 'kick' at the relevant revs anymore.
However, I tried unplugging the MAF for my journey today and the car seemed to run better, less lumpiness, better power and less fuel used.
Would MAF be a fair conclusion? And should it be at full power without the MAF, or a bit restricted?
Certainly sounds a reasonable assumption.
The GTV simply wouldn't run at all when the MAF died, unplugged it and it was fine. Replaced the MAF and we're back on top form. It actually ran fairly normally without the MAF.
A friend's Yaris snotter was running badly, unplugged the MAF and it soldiers on to this day taking full abuse.
At least on LS engines, low RPM the ECU will use a blend of predicted airflow tables and that measured by the MAF, above half rpm or so it'll just use the MAF. If your MAF was failing / giving crappy data, then that will throw the fueling out and could indeed cause odd behaviour.
Generally the MAF is a honeycomb type mesh to control the airflow and then a wire suspended behind it. It is calibrated from the factory to the flow conditions expected where it is housed. If you've made any changes to the intake path that it lives in, or if say there's a fly wedged in some of the mesh, it will affect the flow and the values will no longer be accurately calibrated.
With the MAF failed, it will vary by engine what it does. Again on LS engines, they default to the low octane spark table, what the M3 motor does I don't know...
The GTV simply wouldn't run at all when the MAF died, unplugged it and it was fine. Replaced the MAF and we're back on top form. It actually ran fairly normally without the MAF.
A friend's Yaris snotter was running badly, unplugged the MAF and it soldiers on to this day taking full abuse.
At least on LS engines, low RPM the ECU will use a blend of predicted airflow tables and that measured by the MAF, above half rpm or so it'll just use the MAF. If your MAF was failing / giving crappy data, then that will throw the fueling out and could indeed cause odd behaviour.
Generally the MAF is a honeycomb type mesh to control the airflow and then a wire suspended behind it. It is calibrated from the factory to the flow conditions expected where it is housed. If you've made any changes to the intake path that it lives in, or if say there's a fly wedged in some of the mesh, it will affect the flow and the values will no longer be accurately calibrated.
With the MAF failed, it will vary by engine what it does. Again on LS engines, they default to the low octane spark table, what the M3 motor does I don't know...
Edited by SturdyHSV on Thursday 8th May 09:50
You would be far better asking in the BMW M-car forum.
http://www.pistonheads.com/gassing/forum.asp?h=0&a...
http://www.pistonheads.com/gassing/forum.asp?h=0&a...
Check for leaks in the air intake, sounds like unmetered air entering in somewhere. Inspect for splits in the bellows pipe that run from the MAF to the manifold plus there are pipes under the intake manifold that need checking. It's worth taking the manifold off and checking it all out as then you can also check the oil separator underneath which if hasn't been touched will no doubt have rotten pipes by now.
Only then would I investigate the MAF.
Only then would I investigate the MAF.
If it runs better with the MAF diconnected, the MAF is probably at fault. With the MAF disconnected it will probably drive at 90-95% (default settings).
In the past when I've suspected a MAF I've put a new one in to try. I get all my part from the same place so they're quite flexible in letting me try bits (obviously only bits which they can put back in the box and reell).
In the past when I've suspected a MAF I've put a new one in to try. I get all my part from the same place so they're quite flexible in letting me try bits (obviously only bits which they can put back in the box and reell).
Thanks all, deliberately didnt post in the MPower section as I felt up it would bring up lots of (irrelevant) faults... I've replaced all of the vacuum pipes etc in recent memory so it's not that.
I really want to decide whether it's worth replacing the MAF first. It is booked in for diagnosis next week however this seems such an obvious main cause that it might be futile to NOT replace it!
I really want to decide whether it's worth replacing the MAF first. It is booked in for diagnosis next week however this seems such an obvious main cause that it might be futile to NOT replace it!
Changed it on my E240 (similar symptoms, including no kick down from auto) and it transformed the car. Trouble is the Original Bosch one was in excess of €330 so opted for a cheaper (I assume copy) one for €36 and so far has worked perfectly (touches wood and say's to self, why did you bloody say that...).
tony wright said:
Changed it on my E240 (similar symptoms, including no kick down from auto) and it transformed the car. Trouble is the Original Bosch one was in excess of €330 so opted for a cheaper (I assume copy) one for €36 and so far has worked perfectly (touches wood and say's to self, why did you bloody say that...).
That's very interesting and thanks for posting. I'm not sure how the VANOS timing unit detects engine speed but it could well clear up a few symptoms. 150bhp said:
Would there be any detrimental effect on the engine by leaving the MAF unplugged for long periods of time apart from poor fuel consumption?
Shouldn't be. It restricts performance slightly but just runs on a default map. And the fuel consumption went up measurably on mine with it removed!!
Interesting. My MAF has been playing up (Audi S4 B5) so I disconnected it and the performance is night and day, so much more powerful plus better fuel economy! I ordered a new MAF but was out of stock so been using it for the past couple of weeks disconnected. Ordered another one now though and should be here in a few days, wonder what the performance/economy will be like compared to disconnected??
In most cases with the MAF disconnected or just giving impossible readings the ECU will try and work out the incoming air by using other sensors. This usually means from the throttle position sensor plus air temperature sensor if fitted. How successful it is depends on the complexity of the sensors and ECU, newer cars will fair better.
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