Performance degradation

Hello,

'I have an A3 with an 81 kW (AHF) engine, and I'm experiencing the following problem: Four weeks ago, the car could reach 205-210 km/h according to the speedometer, but now it's limited to 195 km/h. The timing belt was recently replaced on this car.' Okay, I've now read the data using VAG-COM, and the following issues have been detected.

Idle: Duty cycle for the fuel injection start valve (Group 4, Field 4) is between 2.7 and 3.1; the target value is above 3 -> I think this is probably still okay, though??

Full load:
(Group 0, Field 10) Air mass intake = 225-235 -> Target: 255

(Group 10, Field 1) Air mass is = 750 - 810 -> Target is 800 - 1100.

All the remaining values are correct.

Okay, so my question is: the LMM (likely referring to a lung function measurement device) already cleaned it today, but it didn't help much, or at all. Before that, the values were even worse, about 10% lower.

Thank you very much.
In advance.

Best regards, gas stove.

Hello,

Please check the target and actual values for the injection timing in the higher RPM range and under full throttle (it's possible that the injection timing was incorrectly adjusted after the timing belt replacement).
Similarly: Check the fuel line from the diesel filter to the injection pump for air bubbles or foam when accelerating.

Best regards, Rainer.

These are the values recorded during full-throttle acceleration in third gear.
(Group 4)


3087 10.3 10.1 76.1
3150 10.8 11 74.5
3255 11.4 11.2 79.7
3360 11.9 12.1 81.7
3444 12.5 12.5 78.9
3549 13 13 80.1
3633 13.2 13 81.7
3738 13.6 13.6 80.9
3822 14.1 14.3 81.7
3906 14.5 14.5 80.5
3990 15 15.4 82.1
4074 15.2 15.2 82.1
4137 15.2 15 81.3
4200 15.2 14.7 82.5
4284 15.2 15 79.7
4326 15.2 14.7 79.3
4389 15.2 14.7 80.1
4431 15.2 15.2 79.3
4494 15.2 15 80.9
4515 15.2 15.2 76.9
4536 15.2 15.2 75.3
4578 15.2 15 72.9
4578 15.2 15.4 76.1
4599 15.2 15.6 74.9
4620 15.2 15 71.7
4620 15.2 14.5 72.1
4641 15.2 15.4 70.1
4662 15.2 15 69.7
4662 15.2 15.8 68.5

Okay, so the diesel filter and the line to the pump are also fine. The filter and everything else is brand new because the vehicle was recently serviced at an Audi dealership.

Best regards.

Gas stove.

Hello,

"The values look good! Perhaps you could temporarily adjust the target values for the Long-Term Multiplier (LMM) downwards using the engine control unit adaptation function. Instructions on how to do this can be found in the error database under 'Adaptation Channels'." If it then works better, it's probably due to the mass airflow sensor (MAF); be careful, this is just a hypothesis because I haven't tried it yet to see if achieving full power is possible with simultaneously lower target and actual values of the MAF; but the experiment costs nothing .
Please also check the turbocharger's boost pressure system for leaks, especially the clamp that connects the rubber hose from the turbocharger to the plastic pipe leading to the intercooler.
"This clamp must be removed during timing belt replacement, and it has come loose twice before I replaced it with a hose clamp (background: if you lose compressed air in the intercooler system, the engine cannot reach its full power and it smokes black because the diesel fuel cannot be completely burned)."

Best regards, Rainer.

PS: Everything is fine here as well, it seems you might have encountered some resistance .

'Are you talking about the pipe that runs past the diesel filter (the suction pipe)? Is everything sealed properly there? The hose runs from the intercooler to that pipe, and then to the exhaust gas recirculation valve.'

I'll try testing the adaptation process, but I think it might be related to the mass airflow sensor (MAF). Here are some MAF values I logged (before the adaptation):

975 959 2193 100 11.04
770 959 1836 100 11.96
780 959 1877 100 12.88
780 959 1948 100 13.8


That was group 10, operating at 2400 to 3200 RPM after the LMM cleaning.

Okay, I'm going to perform an adaptation now and see what results.

I've already tried the adaptation, but it doesn't change anything. However, I noticed that the mass airflow sensor (MAF) shows the correct target values at low RPMs, but as the RPM increases, the actual values deviate more and more from the expected 850 (target value when accelerating hard). The value is then around 650.

Sincerely,


Gas stove.

Hello,

bad (expensive), it also looks like an LMM to me .

Best regards, Rainer.

Rainer K. wrote:

Hello, bad (expensive), it also looks like an LMM to me . Greetings, Rainer

Hi everyone,

I see it that way too.

But before buying a new one, I would still try cleaning it with brake cleaner spray.
Normally, nothing breaks as a result of that, and with a bit of luck, it will start working again at full power.

Yes, I think so too. I checked all the connections again today, and everything seems to be secure. So, it looks like the bill will be €280. But what can one do?

But thank you for the help, Rainer.

Sincerely,

Gas stove.

Hi, I've taken another measurement, and now I have a few more questions for the experts in this forum. Here are the data: this is group 11, at full throttle, reading 3. Gangg.

0.46 903 1061 979 24.7
1.38 987 1510 1000 24.7
2.3 1113 1540 1051 24.7
3.22 1260 1591 1112 25.5
4.14 1428 1703 1204 25.5
5.06 1596 1785 1346 27.5
5.98 1827 1887 1642 41.8
6.9 2079 1948 2060 62.6
7.82 2373 1948 1979 61.8
8.74 2625 1948 1826 57
9.66 2898 1948 1877 56.6
10.58 3150 1948 1969 60.2
11.5 3402 1948 1958 63
12.42 3633 1948 1918 63
13.34 3864 1948 1938 63.4
14.26 4074 1938 1958 64.9
15.18 4263 1907 1897 64.1
16.1 4410 1846 1846 63.8
17.02 4536 1775 1785 64.9
17.94 4641 1663 1673 63.4
18.86 4704 1581 1571 63

And this is group 10 (which were measured simultaneously).

0 295 959 979 7.8
0.92 415 959 979 100
1.84 445 959 1020 100
2.76 455 959 1081 100
3.68 495 959 1153 100
4.6 545 959 1265 100
5.52 670 959 1459 100
6.44 870 959 1867 100
7.36 970 959 2193 100
8.28 805 959 1856 100
9.2 780 959 1836 100
10.12 800 959 1928 100
11.04 790 959 1979 100
11.96 760 959 1948 100
12.88 740 959 1918 100
13.8 730 959 1948 100
14.72 700 959 1928 100
15.64 660 959 1867 100
16.56 625 959 1816 100
17.48 575 959 1724 100
18.4 525 959 1612 100


Okay, here are my questions now:

1. Is the mass airflow sensor (MAF) faulty now, or not?
2. When you rev the engine from 1000 RPM to 4500 RPM in 3rd gear with full throttle, the mass airflow sensor (MAF) should display at least 850 mg/h from 3000 RPM onwards. However, should the MAF reading decrease again as the RPM continues to increase?

Sincerely,

Gas stove.

Hello,

The LMM values are too low in the higher RPM range. So, either very little air is being drawn in here (due to a blocked intake path, for example), or the mass airflow sensor (MAF) is giving a false reading.
At approximately 4200 RPM, you're getting 700-660 mg/stroke, even though the boost pressure is okay. However, as you increase the RPM further, which is necessary to achieve the maximum speed, these values decrease even more.
The values I measured (using an AHF engine) in the 'paper air filter vs. fabric air filter' comparison are typically around 850 mg per cycle at 4200 rpm.
However, I have a turbocharger and a moderate increase in boost pressure, so the values are definitely higher and should be enjoyed with caution.

Perhaps someone else has comparison data for the standard engine?

Best regards, Rainer.

Hello,

Today, I installed a new mass airflow sensor, but I didn't notice any improvement. What could be the only possible cause of the performance loss?

Sincerely,

Gas stove.

Gasherd wrote:

Hello, Today, I installed a new mass airflow sensor, but I didn't notice any improvement. What could be the only possible cause of the performance loss? Sincerely, Gas stove

Hi.

I wrote something about a change in the ZR (Zylinderkopf, cylinder head) above.
If the problem has been occurring since that specific time, it's possible that an incorrect timing of the camshaft sprocket, leading to incorrect valve opening and gas exchange timing, could be the cause?

Just a thought, I don't have any practical experience in that area...

Yes, that might be possible, but how do I check that?

Gasherd wrote:

Yes, it might be, but how do I check that.

Hi.

According to the repair manual: Remove the valve cover, set the engine to top dead center (TDC), and center the feeler gauge at the timing chain end of the camshaft.