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  #1  
Old 3rd April 2021, 09:07 PM
vajper vajper is offline
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Default TDI 4.2 EGR/gas recirculation

During the last year I have had the MIL light come on every now and then, caused by EGR errors.

Typically the error codes has been "Insufficient Flow Detected" and "Insufficient Flow - Intermittent" mostly on the right cylinder bank but at some point also on the left one.

I have removed the EGR valves and they looked fine, not much sooth build-up and have also run the output tests on them and notice that they seem to follow the control signal opening and closing.

I also replaced the right EGR valve with a almost-new one that I ran into. Problem is still there and even though I haven't disassembled the return manifolds to ensure they are not clogged, my gut feeling says they are not worse than the valves (which were OK).

I guess there is some sensor that is used to actually measure the return gas flow. I would have guessed a temperature sensor but don't see anything like that in the region around the ERG valve. How is the flow measured?

Any suggestions what to look into?
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Old 4th April 2021, 10:02 AM
ainarssems ainarssems is offline
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As far as I know there are no meters for EGR flow. It is estimated from the MAFs. If the ECU expects 500mg all flow in cylinders at given manifold pressure and rpm and MAF is measuring 300mg air then 200mg must be EGR flow

Or to put it other way there are maps in ECU that specify air flow depending on rpm and injected fuel amount. ECU then adjusts EGR to reach the specified airflow. There are some limits of how much it expects to open EGR valve to reach that specified airflow. If the ECU needs to open valve more or less than those limits to reach specified air then it will throw error code.

In your case it is opening EGR more than it is expecting and measuring higher airflow that it is expecting. You could try looking at MAFs
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Old 5th April 2021, 07:11 AM
vajper vajper is offline
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Guess I'll need to look at the MAFs. Not the first time they may be the suspect in a motor
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Old 5th April 2021, 09:38 AM
vajper vajper is offline
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Did a quick test, not sure what the three values means in group 3 on the two ECU's, I'm used to one "expected" value and one measured value. In this ECU there are three values for air mass. The second and third ones are following each other pretty tight, the first one is usually higher when pushing the engine. both ECUs/banks look more or less the same.

If the first one is the expected value, then maybe there might be a problem with the MAF readings but still the readings go up to at least 1200mg/stroke.

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Old 5th April 2021, 06:15 PM
ainarssems ainarssems is offline
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Yes, no labels for 4.2TDI in either VCDS or OBD11,if I get some time I will see if I can find my VAS5054 and check what each of those three airflows represent. Although 1500 seems a bit high. Not backed by any facts but I would have thought it should top out at about 1200-1300.
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Old 5th April 2021, 06:25 PM
vajper vajper is offline
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Was out driving trying to cure my transmission and get proper adaptations in place so I also tried to rev the engine with gear in N. Any high RPMs trigger the EGR flow error. I actually couldn't rev the engine up to the red line (4200 rpm or so), not sure if that is a software limit or is an indication of MAF problems. I only reached about 3700 rpm.

When revving it, again the first value goes up to about 1400 mg/str but value two and three stays way lower. Again same for both engine banks.
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Old 7th April 2021, 09:48 AM
ainarssems ainarssems is offline
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I have not dug out VAS5054 but I did a quick test with OBD11 on mine.

I think in group 3 1st block is requested airflow, 2nd block is measured airflow bank 1 and 3rd block is measured airflow bank 2. I only did stationery test revving up engine up to about 2500rpm, did not want to rev higher on cold engine, All 3 values changed between 300-900. 1st block changing first and blocks 2 and 3 following it with a little delay.
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  #8  
Old 11th April 2021, 06:57 PM
vajper vajper is offline
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Thanks for checking out, much appreciated

Next weekend I plan to tear down the transmission sump again and while on jack stands remove the front wheel housings and clean the MAFs. Let's see if that's enough...
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Old 5th May 2021, 10:25 AM
vajper vajper is offline
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When doing some transmission work during the weekend I pulled both MAFs and cleaned them thoroughly using MAF cleaning spray. Didn't seem to change a thing

Still I get the EGR insufficient flow MIL warning when revving the engine and the air mass measurements are off.



Haven't dropped the MAFs yet. Can it be that the requested flow should be the sum of the real bank 1 and bank 2 flows? If yes, then it might be that things are OK. If not, the MAFs are definitively bad.
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Old 5th May 2021, 10:39 AM
vajper vajper is offline
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This is what the sensors looked like. Other MAFs seems to have a glass bead more like an old diode in the middle while my sensors just have a smaller diameter bead.





Found an image of a new Hitachi sensor of same model and it had the same diameter on the bead as my sensors. Guess that doesn't tell anything about them
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