Normal MAF readings at Idle?

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NickSTi7

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Hey Good Evening, just wondering if anyone knows what a healthy MAF should be reading at idle on a 2.0 TFSI, stock? Also, on the 18.2 update of the VCDS I can't find where to view fuel trims, are they supposed to be in block 032?
 
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Uwe

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If this is newer car, with an ECU that uses the UDS protocol, there will be no "blocks". There are only individual items.

Can you post up a scan from this car please?

-Uwe-
 
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DrPeter

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Hello,

Hey Good Evening, just wondering if anyone knows what a healthy MAF should be reading at idle on a 2.0 TFSI, stock? Also, on the 18.2 update of the VCDS I can't find where to view fuel trims, are they supposed to be in block 032?

An Auto-Scan is always helpful :)

If you ask me, engine at idle, no load at sea level, you should see on a 2.0L engine about 3.4 to 3.6, maybe a little more, 3.8g/sec. about 1.8g/sec per liter.

This is sort of my personal rule of thumb and what I do, no guarantees with this. I use a value of about 1.7g/sec to 1.9g/sec then multiply this by the displacement of the engine. Now this was done on a healthy engine, no false air leaks at idle (No Loads, AC off) while at sea level.

- So for the 1.8L turbo at idle, the engine should flow about 3.02 to 3.42g/s.
A lower value of course could be due to false air or vacuum leak, a higher value could indicate a dirty MAF or air-box air flow issues or even wrong parts in both cases.

Once again, this is kind of a general rule I use and if you re above sea level , take away a little, few tenths of a g/sec per 500'. - That is mostly SWAG on my end.


There is the full throttle/full load test others use and that is measure the MAF sensor readings at full throttle in 2/3 gear and the engine at maximum rpm. The value you get, 'should' be ~80% of the rated horsepower.
- So for example the 1.8L turbo engine, rated at 180hp, should have a max flow of about 144g/s. I suggest to data log the values and then review, concentrate on driving, let VCDS do the logging work. Be SAFE!

I have not scientifically proven or dis-proven any of these methods, I am sure there is a more exact way to calculate flow, but as a dealer tech, I just needed to be close, not necessary exact in order to condemn a MAF sensor.

Hope this helps,

drpeter

PS.. Anyone got any other ways to check the MAF sensor? _ Ideas, comments are welcome...
 
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Uwe

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There is the full throttle/full load test others use and that is measure the MAF sensor readings at full throttle in 2/3 gear and the engine at maximum rpm. The value you get, 'should' be ~80% of the rated horsepower.
I'm going to be pedantic here, but the peak MAF value likely won't be found at "maximum RPM" (which I take to be either the beginning of the red zone on the tachometer or the wherever the rev limiter kicks in). It will be found at whatever RPM the engine produces peak horsepower, which is usually 500-1000 lower than "maximum".

As for the accuracy of this test: It takes a predictable amount of air and fuel flow to produce one horsepower. There will be minor differences from engine to engine, but they won't be major. What can throw this test off quite a bit is altitude, particularly on a naturally aspirated engine. Naturally aspirated engines can only produce rated horsepower at sea level because the air flow through them drops as the ambient pressure drops with increasing altitude. However, this is generally not a factor with turbo-charged engines; the turbo just works a little harder to compensate and produce the desired manifold pressure.

-Uwe-
 
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Jack@European_Parts

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PS.. Anyone got any other ways to check the MAF sensor? _ Ideas, comments are welcome...

I have found that using the MAF readings the controller reports has been an unreliable means in diagnosis from the beginning of automotive time unless mechanical sweep potentiometers. It seems to permit issues that hide outside the scope of measuring block values or the diagnostic stack of controllers & widespread across all manufacturers.

As you aforementioned Peter & is a good point is questioning if the correct part number is in the car and than there is the whole FOD aftermarket issue and the fact the OEM MAF's plain suck the big one.

First what I have done is stock each part number & which are known to be in proper working order & consider them as a tool for each engine code.

Second.......and you guys are going to make fun of me but full on nerd we go.

I qualify the MAF outside the car not in it during operation due to cross check crap.

I made a bench flow tester to measure the MAF charted.
I do this by sucking air through a MAF with a 5HP vacuum cleaner & that I can change the air flow settings with a regulator & TV to simulate the changes of boost bypass and throttle plate deviation off idle.
I plug an ECU into it on the bench and watch/log blocks live data with VCDS and a scope on record.

I had to do this for testing aftermarket air mass meters & qualifying OEM's or to compare when I didn't have cars to test on.

All I can tell you is I am very disappointed with the degree of deviation permitted & before a DTC is reported!
I personally think a MAP sensor would be much more predictable.

WTF good are test settings using the controller OBD & if only they report as in spec or fine and then the thing still runs like poop?

Long and short term trims have always been a much better way of determining what is going down for me!
 
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