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Came out yesterday morning car wouldn´t start, lot´s of juice on the battery, no cranking, after numerous tries the starter finally gave in and started cranking but barely turning the engine. The engine started after a couple of tries.
Then I started my trip to work and found the car with no power at all, had my VCDS in the car and connected it up. No faults in ECU memory, but my boost pressure was very low, around 0,6 bar @ 2000-3000rpm (7 psi). I put the car in neutral and kicked the accelerator a couple of times, the final time I did this something happened when the engine went over 4000rpm, it felt like power was restored, and the engine had a lot better throttle response (in neutral still). I tried to doo a couple of runs from low to high rpm, some power was definetly restored, but the engine was still slower than usual. Had a look in VCDS again and the MAF reading was stuck at 550mg/str.
Stopped again pulled og the connector to the MAF, no change in reading or engine response/power.

Do any of you clever guys have any ideas what happened to my car, and any procedure for checking the MAF "hot wire" on a mk3 TDI engine code AFN. I have found a lot of write-up´s for the mk4 MAF, but none for the mk3.....

Best Regards and power to the "do it yourself people"

Anders Fiedel
 

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Bad starter could have been a loose or corroded wire at the starter or a bad solenoid. http://www.myturbodiesel.com/1000q/multi/starter-fix-removal-mk3-mk4-VW.htm Take a look at this article for some ideas.
Hey,
Pulled the starter off the gearbox today and found the bolt which the wires for the alternator and battery connects to was broken at the starter end, fixed it with a new starter, now it cranks perfectly :nana2:

I also had a go with the ECU/MAF today yesterday it was measuring 550mg/str constantly, todays value is 30mg/str. when connected and 550 when disconnected. No change in MAF reading when applying throttle. Went over all the wires again, from MAF connector to ECU, all were good, so I am pretty convinced that the MAF is faulty, only thing that annoys me is that when I take the MAF apart and measure the hot wire I can se that it reacts to thermal changes, so the sensor interface in the MAF must be dead. Maybe I should investigate this someday.

What do you think folks, should I just go by myself a new MAF ???
 

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:thumbsup

I hate throwing parts at a problem unless you're 95% sure it's the problem. If you do find out how the mk3 MAF works and normal vs. abnormal readings, please share. If you take step by step pictures, screenshots, and do a writeup, it will qualify for the writeup contest and help many others.
 

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Hi
The permanent MAF value of 550 mg/stroke indicates that the ECU replaces a non-credible or bad MAF signal. There should however occur an error 00553 in connection with that.
From the part number the air volume meter of the AFN (up to 1998) and my 1Z should be identical (074 906 461).
You can therefore do the following electrical check of the air volume meter supply. Open the connector at the air volume meter and measure with ignition on:
- voltage between contacts 3 + 1 and 3 + ground, should be battery level;
- voltage between contacts 1 + 5 and 1 + ground, should be 5 Volts;
contact 1 is the lower left one when you look at the connector housing with the smaller housing radius on left side.
contact 2 is the upper left one, contact 3 is lower middle, etc.
Regards
 

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Discussion Starter #7
I did measure the supply voltage and the reference voltage for the MAF and the are fine, 12.8V with ignition on and 14.2V with engine running, the ref. voltage is 4.98V
Hopefully I can borrow another MAF today to see if readings are better.

Status :
MAF plugged in : VCDS reads = 30mg/stroke. (very low on power, and it will only rev to about 2800rpms)
MAF unplugged : VCDS reads = 550mg/stroke (power at about 50% but it will rev to redline) default ECU value as mentioned by audi1z
 

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Discussion Starter #8
Replaced the MAF this evening and power is restored, got a used one from a friend of mine for testing.
VCDS shows a bit of a offset between expected airflow and measured airflow, the curves do follow each other.
The MAF I put one measures about 490mg/stroke at idle and expected is 285mg/stroke, when I floored it in 3rd gear @ 2200rpm the measured value went to about 900mg/stroke. So it seems that the MAF is doing what it should. But doesn´t it seem that my turbo is overboosting a bit and then backing of ?

(The second "run" is in 3rd gear from 2200rpm to redline)



I will do some more testing tomorrow.
 

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Hi,
The air volume meter needs to be replaced, no doubt.
Regarding the turbocharger, you can perform another test (I have only manufacturers values for turbocharger check with a 1Z engine, but the AFN should be similar).
Record the MAF values during full throttle acceleration from 1500min-1 to 3000min-1, one check with boost pressure valve N75 disconnected, the other one with N75 connected.
Manifold pressure to be reached at 3000min-1 is 1550 mbar to 1750 mbar w/o N75 operating, 1800mbar to 2050 mbar w/ N75 operating. Note that the values are absolute pressure, I copied them from the service manual. You need to subtract 1000 mbars to have relative values.
May be that the VTG mechanism is a little bit stuck. But Let us discuss further when you have the corresponding results.
The high MAF value during idle might indicate that the EGR is not properly working, but this is for the moment a secondary question.
Regards
 

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Discussion Starter #10
I was actually wondering if my EGR was ok, my EGR reading was about 5% @ wot and between 50-70 @ partial throttle, but your probably right that this is a secondary problem. Lets do one thing at a time :)
Will do the test tomorrow after work.
Have a good night in Germany :)
 

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Hi,
Sorry, but please discard the check of the MAF pressure which I suggested above. This will not work for the AFN engine because of the different principle of MAP control.
I had some minutes to check another source, giving values for the AFN, too.
Pressure values of up to 2500 mbar absolute pressure under full load should be ok, even if slightly exceeding the requested values. A short overshoot under full throttle acceleration in the frame of 2 sec is ok, too. I can only guess the timescale from your posted log, but it does not look bad.
There are two VNT maintenance descriptions here in the forum which you can check further:
http://www.myturbodiesel.com/1000q/a4/VNT-wastegate-adjust.htm
http://www.myturbodiesel.com/1000q/a4/VNT-turbo-removal-vanes.htm
For the moment, I would however not start a maintenance.
Are any fault codes stored in the ECU memory?
Regards
 

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OK I did it on my way home from the airport today (before reading your post) :)

First with N75 disconnected, 1. run from 1500-3000 rpm, 2. run from 1500-redline (almost no boost with N75 disconnected (around 0,15-0.2 bar)

Red is RPM
Green is Espected boost
Yellow is measured boost
Grey is EGR

Secondly with N75 connected, again 1. run from 1500-3000 rpm, 2. run from 1500-redline

Red is RPM
Green is Espected boost
Yellow is measured boost
Grey is EGR

When I do an output test from VCDS I can see the actuator on the turbo is moving, also the EGR solenoid is clicking away.
I do not have any DTC´s (faults) in my ECU, only when I disconnected the N75 :)

And I discovered the hard way that the output test in VCDS also contains a test of the fuel cut-off valve........not practical when you are doing 130 km/h on the motorway.........aaarrrrgggghhhhh...........
 
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