AKN: Troubleshooting Performance & Startup Issues

Hello,

'I've noticed a decrease in performance in my car for some time now. The maximum speed, according to the speedometer, is 214 km/h on a straight road, but the actual speed is likely closer to 208 km/h. The problem has worsened over the past few days.'

-Maximum speed at 210 km/h (as indicated on the speedometer).
-Lower airflow up to 3000 RPM.
- According to the MFA (Multi Function Display), the current fuel consumption in 6th gear within this RPM range is approximately 1.5 liters per 100 km (now about 14.5-15.3, compared to 16.7 previously).
- When starting, the engine doesn't start immediately, but cranks a few times first.




My first thought was the LMM (likely referring to a lambda-air mass meter), because the actual values are slightly lower than the target values. However, since the torque limitation is still setting the lowest value, that possibility can be ruled out.

I also had the camshafts inspected, and while there are some minor signs of wear, they are all below 1 mm.

'Why does the MFA (presumably a diagnostic tool) show a lower fuel consumption (i.e., injection amount) than expected, which also corresponds to the feeling during acceleration, while the log data appears normal?'

I am grateful for any advice.
Regards,
Jean.

Hello Jean,

I'm guessing the LMM is tired. Mine is reading 879 mg.

It never reaches the maximum specified value with you. So, take it to a VW dealership and get a new mass airflow sensor (MAF sensor).


That, however, has nothing to do with the starting problem.



Wishing you continued success.

Rainer.

So, let's go to VW and get a replacement mass airflow sensor.


That's probably my next course of action. Since the lambda sensor probably needs to be replaced soon anyway. However, it's surprising that, according to the logs, the torque limitation is still dictating the lowest injection quantity. Therefore, the lambda sensor cannot be the cause.

Best regards, Jean.

I've done another test run and logged data for group 4. According to the table, the adjustment should be 5-10 degrees at full load. However, it doesn't reach over 5 degrees until 2700 RPM. Could this indicate a problem with the ESP (Electronic Stability Program)? At idle, the throttle position is 100%, and the value is -1 degrees.

Unfortunately, I don't know how to save images from the TDI graph and post them to the forum. This morning, when the fuel temperature was still relatively low, I read the injection start timing, and it was close to the upper tolerance limit at the coordinates 135/65.

As I was just taking another measurement, the value was too far outside (above) the range to be displayed.

In this case, group 4 exhibited a deviation of 4° from the optimal position at a key ratio of 50%.
In the default setting, the range is from: late -1.4°/100% to early 16°/29.6%.
Everything is absolutely within the normal range.

Why is the graph displaying incorrect values?

If the values in the measurement blocks are correct, does a misaligned ESP trip out, or is it completely misaligned according to the graph?

Hello Jean,

The graph isn't working correctly for me either. It seems to be related to the VP44.

To get an image of the graph, press Alt + Print Screen (Print).

Then the image will be copied to the clipboard. From there, you can paste it into another program and save it.

How many miles are on your engine?

Have you ever had your glow plugs checked? Although, you probably don't need them in the current temperatures.

Is your battery still powerful?

See you later, Rainer.

Hi,

Theoretically, with VAG-Scope, you can adjust the specific axis range.
There's a frame around a value field at the bottom. You can move the frame within the fields using the left/right arrow. On the right, you can then enter the maximum and minimum values.

Best regards, Rainer.

Hello,

The car now has 144,000 km on the odometer. The battery is in good condition, and I haven't checked the glow plugs yet. However, it also starts poorly with the pre-glow function, whereas before it used to start 'immediately' without it. Perhaps I should put the starting problem into perspective. It still starts reliably, but I've noticed that the engine needs to turn over a few more times than it used to. Maybe this isn't directly related to the lack of power.

Compression shouldn't be a problem with this kind of mileage, should it?

@ Rainer

Unfortunately, even when expanding the display range, the values for the ignition timing remained far outside the upper limit that defines the tolerance range.

'I've noticed in the logs for group 8 that the torque limit releases above 1400 RPM, exceeding 40 mg/cycle, but then reduces back to 37 mg/cycle above 1600 RPM. You can actually feel this reduction during acceleration from those RPMs, as if the developing torque is suddenly being dampened. I find this to be abnormal. Does anyone have similar logs from this motor?'


Regards,
Jean.

Have you checked the timing belts to see if they are tight?
I once had a colleague who experienced similar symptoms...
Stay cheerful.
OlBe.

Hello everyone,

Today, I installed the new mass airflow sensor, and I also replaced the diesel filter just to be safe. Unfortunately, this didn't solve the problem. Also, my laptop is malfunctioning, so I couldn't create any new logs.



The issue with the timing belt still needs to be checked.

Otherwise, I remain open to all suggestions for solutions.

Regards,
Jean.

'Edit: Does the AKN engine in the Passat have a pre-lift pump? (Unfortunately, the search function has yielded conflicting results.) If so, could a defect in this pump cause insufficient pressure in the fuel system, preventing the ESP (electric fuel pump) from delivering enough diesel? This could also explain the starting problems.'

Hi,
How about your fuel return lines/leakage oil? They tend to fail completely, especially in warmer weather, if they're already old.