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Discussion Starter #1
To cut a long story short with the MAF unplugged the car runs perfect, with it connected it sometimes won't accelerate/rev randomly.

BUT i've tried another MAF only to have the same problem (albiet another used one).

It's a 4 pin one so I'm assuming 2 pins are for the temperature and the other 2 to measure the airflow.

I'm trying to understand what's actually happening in order for it too be faulty. At the minute i'm assuming the sensor is reading there is no airflow? but wouldn't this cause the car to stall or throw up an error?

I'm close to buying a new one but got a funny feeling it's still going to do the same..

Cheers
 

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Discussion Starter #3
I thought it best to start a new thread as it's definately not a turbo issue. Unfortunately the MAF is a sealed unit so can't actually get to the sensors without destroying it. I've poured some IPA through it numerous times but still had the same fault.

I think you're right I might have to bite the bullet i'm just intrigued as to what's actually happening without spending near £200 on a MAF :(
 
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Hi there was a thread on here earlier this week about using the vauxhall maf as its the same but cheaper but can't find the thread. I think you had to swap the sensor from one housing to another .
The way I understand maf's is a heated wire that uses the temp change as air passes over it to determine fuel air mix basically ?
When you say sealed do you mean tamper proof screws or totally moulded sealed ?
 

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I'm trying to understand what's actually happening in order for it too be faulty. At the minute i'm assuming the sensor is reading there is no airflow? but wouldn't this cause the car to stall or throw up an error?
I may be wrong, but, I thought that, with the MAF unplugged, the ECU defaults to some pre set parameters -hence the unplugging makes the car seem better. Those parameters are not ideal, but can assist with diagnosis of the problem.

Also, I believe genuine bosch are the way to go for new mafs. Cheaper/non branded are not as reliable, apparently.
 

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Discussion Starter #6
Hi there was a thread on here earlier this week about using the vauxhall maf as its the same but cheaper but can't find the thread. I think you had to swap the sensor from one housing to another .
The way I understand maf's is a heated wire that uses the temp change as air passes over it to determine fuel air mix basically ?
When you say sealed do you mean tamper proof screws or totally moulded sealed ?
It's a completely sealed unit with no bolts etc.

I may be wrong, but, I thought that, with the MAF unplugged, the ECU defaults to some pre set parameters -hence the unplugging makes the car seem better. Those parameters are not ideal, but can assist with diagnosis of the problem.

Also, I believe genuine bosch are the way to go for new mafs. Cheaper/non branded are not as reliable, apparently.
Even the non Bosch ones are at least £120 but I agree I'd definately buy Genuine
 

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if you have a lead you could try the free version of fes and read direct values off the maf.
read the maf temp and compare to ambient , read the maf airflow at idle expect around 485mg/i and 300ish when egr opens, and when on boost wouldnt be too far off half of the boost pressure as a rough guide, so say max boost 2350mbar= maf around 1175mg/i +/-50mg/i 1800mbar boost=900mg/i maf.
if your maf values are way down you have duff maf or airleak after maf to turbo pipe etc.
 

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Discussion Starter #8
Brought a new MAF but still having the same problem but when the engine is warmed up it seems to be ok. :confused:

So if the MAF is ok, is it possible that the airflow is being blocked to the turbo somehow?
 
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Yes think you're right but can't think of anything else that was cold related. Other than air/fuel mix and you seem to have been through that .
Does it start ok . If so its probably not the glow plugs.
 

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Discussion Starter #14
Have you checked for damage to the pipe between MAF and Turbo?
Yeah it's all ok, had all the intake system apart looking for splits etc but nothing found. I'm going to wait until its cold and log the signals on multiecuscan
 

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If you have a MAF with damaged characteristic then the ECU starts to modify the amount of injected fuel. When you unplug the MAF, ECU immediately "switches" into emergency mode. When you plug another MAF (new or used one) then the ECU starts to use values have been calculated with the former faulty MAF. ECU needs some time to learn the characteristic of new sensor(s) (more precisely set the mixture correction values to have the ideal mixture strength measured by control lambda probe).
Probably that's why the replaced used MAF didn't help in short term, and that's why fist the new MAF didn't help too. If you don't want to wait until ECU learn these, for certain models there is an option in FES/MES to reset the mixture correction parameters.
 

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Discussion Starter #16
Correct me if i'm wrong but whilst changing the MAF the battery is disconnected for a good 30-40 minutes so everything should be reset anyway?
 

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Discussion Starter #18
I have just reset the ECU using multiecuscan and have been on a spirited drive and haven't been able to get fault now so I'm hoping it's gone, although it has done this before then came back out the blue..

BUT..

This time I have a stored fault code!
 

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1403rpm at gas pedal position=0% with warm engine.. if values are reliable then it happened during engine brake.
Anyway I'm not familiar with diesel engine, but as it's written in the description I would delete the fault code and try to reproduce it. If it will appear again then you have to think about the reasons according to the fault code description..
 

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Discussion Starter #20
That's intereting as it seems to do it straight after hard braking but on the way to work this morning completely lost the turbo for 10 miles on the dual carriageway and as I turned into the carpark it came back. Boost sensor next!
 
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