MAF Air sensor, actual is higher than specified ?

   #1  

alik

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Hello,
can someone told me, is my MAF sensor bad?
Car is Audi 80 B4, 1.9 tdi 66kw, 1z engine, and works normaly and no problems with speed or with nothing.
But some days ago, the car shut down while driving, and after that works normally like before. But today again, the car shut down while driving, and i connect VAG COM and see error: "00553-Mass Air Flow Sensor (G70) -27-10 Implausible signal-Intermittent".

Picture of MAF values:







Here is also a video:

[video]https://streamable.com/eqr0y[/video]
 
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dieseldub

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It would appear the EGR isn't working. The duty cycle has commanded the EGR valve to open, but the MAF values have not dropped accordingly.

Now, I will say that I have seen NUMEROUS stock TDIs where the "specified" MAF values are lower than the actual readings, BUT, the EGR duty cycle in field 4 indicates that the EGR is not being commanded open by the ECU. So when I see that, I just tend to ignore it.

However, in your screenshot there, the computer DOES have a duty cycle value that corresponds to requesting the N18 supply vacuum to the EGR to open the valve, yet the MAF values haven't changed.

A test you can do is go to basic settings, same block, 003, and the computer will command the N18 to supply max vacuum, and then release to zero vacuum, back and forth repeatedly.

Field 2 will alternate between "ON" and "OFF". When it reads "ON", the vacuum coming out of the N18 should be the same as system vacuum (typically 25" mg or more). When it switches to "OFF," the vacuum should immediately drop to 0.

Using a vacuum gauge you can easily verify if the N18 is outputting the correct amount of vacuum or not. If it is not, measure if the vacuum being supplied into the valve is adequate or if there's a leak somewhere before the N18 or a bad vacuum pump (very rare).

If it IS getting adequate vacuum into the N18, but not much is coming out, you likely need a new n18.

If you are getting the correct vacuum as the basic setting test switches between OFF and ON, then try manually applying vacuum to the EGR valve with a hand vacuum pump, see if it holds vacuum, remove the hose from the intake manifold and put your eyes on the valve itself, as you apply vacuum see if it opens at all. If not, you need a new EGR, which on a 1Z is unfortunately integrated into the intake manifold...

When the system is working correctly while you're running that basic setting 003 test, you should see the MAF values change as the N18 is commanded fully on and fully off. When field 2 reads "ON," with a porperly working system you might see the MAF values drop to 180-250 mg/st, when it's switched to "OFF," it normally reads somewhere North of 400 mg/st like yours is currently.
 
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