AJM Issue: Short Burst, Then Slow Speed

Hello,
Perhaps someone can give me a tip about the following problem:

Here's the translation:

'This is a Golf 4, manufactured in 2000, with 132,000 kilometers on the odometer. The engine code is AJM, and everything is original. It has been 'maintained by a workshop,' meaning all inspections, including the fuel filter, oil changes, and timing belt replacement, have been performed.'

Last week, I was driving on the highway (in a friend's car), and I noticed that the car wasn't as fast as it used to be.

It's quite noticeable, for example, when you try to accelerate (full throttle) at (over 2000 RPM). You get a 'boost' for about 1-2 seconds, but then it feels like the turbo pressure is being reduced. The car continues to accelerate, but only very slowly. This happens with every acceleration, but it's only really noticeable above about 2000 RPM.

Can anyone give me a tip as to what might be causing this, or perhaps provide some data for this engine? What values should the mass airflow sensor (MAF) be providing, or what should the boost pressure be for this engine?

The error memory shows nothing (unfortunately).

According to my friend, the car doesn't consume an unusually large amount of fuel (5.5 liters per 100 km) or oil (0.5 liters every 10,000 km).

He can only reach the top speed (195) when going downhill after a very long run-up.

Best regards,

Hello,

It sounds like it could be related to the LMM (likely a sensor issue) or a stuck VTG (valve train gear). A log of measurement group 3 would be helpful in this case. Otherwise, the usual methods for checking the VTG linkage apply. The following technical article should help https://community.dieselschrauber.org/en/viewtopic.php?t=3004.

I had the same problem with mine, and it turned out to be the mass airflow sensor.

Don't have the workshop install and uninstall it; do it yourself.
Otherwise, you've probably paid 30-50 euros too much.

VW wants to only charge 75 euros for a new one!

decell wrote:

... or possibly data related to this engine? What values should the mass airflow sensor (MAF) provide, or what should the boost pressure be for this engine?

... there are specialized articles on that topic ...

http://www.dieselschrauber.de/Solldaten_4_Zylinder_PD.html

and the AJM should include all target values.

Thank you for your help. I'll check that out this weekend and post the results here in the thread.

Best regards,

...it took a little longer , but now I've done a test run using VAG-COM:

ftp://test:[email protected]/003.xls
ftp://test:[email protected]/008.xls
ftp://test:[email protected]/010.xls
ftp://test:[email protected]/011.xls


Here are three things I noticed:

The mass flow controller requires 850 mg/H (measurement block 003, normal value 850-1050), but the actual mass flow rate remains below 700 mg/H on average.

2. The torque limitation (measurement block 008) is always above the smoke limit.

3. The boost pressure (measured by sensors 10 and 11) takes quite a long time to stabilize, which is why there's a noticeable drop in torque just above 2000 RPM. Could this be related to a faulty mass airflow sensor (MAF)?

I checked the VTG function according to the instructions.
After the engine starts, the rod retracts approximately 1 cm towards the diaphragm housing and moves a few millimeters back and forth when the accelerator pedal is pressed. -> Just as described...

What do you think about the data?

Best regards,

decell wrote:

...1. The oxygen flow meter requires 850mg/H (measurement block 003, normal value 850-1050), but the actual mass flow rate remains below 700mg/H on average.

Hi,

The highest value for air mass/pulse is approximately 770mg/pulse in your case. This indicates a faulty mass airflow sensor (MAF) (a minimum of 850..1050mg/pulse is expected).
Before you make any further assumptions or look for errors that might not actually exist, try replacing the mass airflow sensor (MAF sensor) first.

@ Bertil:
If I understand you correctly, your next step would be to replace the mass airflow sensor (MAF), and then see what happens. Perhaps point 3 will then be working correctly again.

I'll wait until January, or are there already any retailers offering the mass airflow sensor for around 80 euros?

Greetings and thanks .

decell wrote:

@ Bertil: If I understand you correctly, your next step would be to replace the mass airflow sensor (MAF), and then see what happens. Perhaps point 3 will be working correctly again after that.

Yes, exactly like that.
First, fix the error and then see if everything else was just a "side effect" (which I suspect).

For the records...

I had the same problem with my 2000 AJM as the original poster, except that the top speed (210 km/h according to the speedometer) was easily reached, but the acceleration sometimes dropped to almost zero around 160 km/h.
After reading this and other threads that pointed to either the mass airflow sensor (MAF) or a stuck variable turbo geometry (VTG) adjustment as the cause, I decided to try replacing the MAF sensor. That turned out to be the solution, and all the symptoms described here in the original post have disappeared.

I hope to contribute something to error reduction .

Hi,
I experienced the exact same issue: The cause was a faulty solder joint in the op-amp circuit, which was carelessly assembled for testing the boost/control pressure. (Addition: In *my* op-amp circuit, which I carelessly assembled for testing.)

In short: If the boost pressure signal fails, the system detects this and switches to a limp mode without the glow plug warning light flashing.

Effect: Normal driving is possible as long as you stay within the range where the turbocharger pressure builds up properly after starting. If you give it too much gas – a short burst of acceleration – it will become sluggish and remain in that state.

The easiest way would be to log the signals using VAG-COM.
For the LMM, I recommend performing a diode test BEFORE purchasing a new one.

garth.brooks wrote:

Hi, I had exactly the same effect: the cause was an open solder joint in the carelessly soldered OP-amp circuit used for testing the boost/control of the charging pressure.

Hi Garth,

Which component are you referring to?
A fake electronic component to tamper with the turbocharger pressure sensor in order to increase boost pressure, or any original part .

Hi Ulf,

'It's a fake electronic system that controls the boost pressure in a way that I imagine, lower at partial load due to the lower exhaust backpressure, and higher at full load because of the visible fuel in the exhaust = soot. And there's a function that, at 1.3-1.4 bar, makes the engine electronics display 1.4 bar again, so that it returns to the target boost faster, but this tends to cause surging - I'm not finished with it yet, that's why I'm tinkering with it.'

I also need the elevation for the gas introduction; I haven't completely given up on that yet. Currently, I'm using an analog computer with a 4x operational amplifier.
It sounds complicated, but it's still simpler than a microcontroller.

garth.brooks wrote:

A fake electronic system that controls the boost pressure as I imagine, lower at partial load due to the lower exhaust back pressure, and higher at full load because of the visible fuel in the exhaust = soot, & a function that, at 1.3-1.4 bar, makes the engine electronics "pretend" to be 1.4 bar again so that it returns faster, but this tends to cause surging - I'm not finished with it yet, that's why I'm tinkering with it.

Hi Garth,

That sounds interesting.

Is the control unit integrated into the sensor circuit (like a boost pressure control unit), or is it more of a self-regulating system based on pedal position, air mass, and/or engine speed?

in the sensor loop, more precisely, as a free-standing structure inside/on the cable. Many cables are going somewhere else. It's not working quite the way I want it to yet, so I don't want to write too much about what's not working properly. I've been working on it for a while, but the weather is too cold for tinkering, and my wife wants a new nest and is keeping me busy with tasks.

I think I observed that simply screwing the turbocharger's wastegate adjustment screw upwards causes it to build pressure even when it doesn't actually need to. (at low partial load). While it responds incredibly quickly, it ends up consuming more fuel due to the constantly higher exhaust backpressure. So, I started experimenting...

Okay, in my case, the boost pressure isn't as high under partial load. At around 1,900 RPM, while maintaining a speed of 100 km/h, I'm seeing approximately 0.2 bar of overboost.

Best regards, WarLord.