Problem with AJM: short burst of power, then only slow acceleration

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

It's a Volkswagen 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 fuel filter, oil changes, and timing belt replacement, have been performed.

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

It's very noticeable, for example, when you try to accelerate (full throttle) at (over 2000 RPM). There's 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 attempt, although it's noticeably only above approximately 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 reading, or what should the boost pressure be for this engine?

The error memory shows nothing (unfortunately).

According to my friend, the car neither consumes an unusually large amount of fuel (5.5 liters per 100 km) nor oil (0.5 liters every 10,000 km).

He can only reach the top speed of 195 km/h when going downhill after a very long run-up.

Best regards,

Hello,

It sounds like it could be related to the LMM (likely mass measurement) sensor or a stuck VTG (variable turbo geometry). A log of measurement group 3 would be helpful in this case. Otherwise, please refer to the usual methods for checking the VTG actuator. The following article may be helpful: /viewtopic.php?t=3004

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

Don't have the workshop install and uninstall it; do it yourself.
Otherwise, you've probably paid between 30 and 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 MAF sensor provide, or what should the boost pressure be for that 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. I'll post the results here in the thread.

Best regards,

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

ftp://test:test@decell.mine.nu/003.xls
ftp://test:test@decell.mine.nu/008.xls
ftp://test:test@decell.mine.nu/010.xls
ftp://test:test@decell.mine.nu/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 emission 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 back and forth a few millimeters when the accelerator pedal is pressed. This is exactly as described...

What do you think about the data?

Best regards,

decell wrote:

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

Hi,

The highest value for air mass/stroke that I'm seeing from your data is just under 770 mg/stroke. This indicates a faulty MAF sensor (Mass Air Flow sensor), which should ideally be in the range of 850 to 1050 mg/stroke.
Before you make any further assumptions or look for errors that might not actually exist, try replacing the mass airflow sensor (MAF) 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 also be working properly again afterwards.

I'll wait until January then, 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 also be working again afterwards.

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

For the records...

'I had the same problem with my 2000 AJM as the original poster, except that I could easily reach the top speed (210 km/h according to the speedometer), but sometimes the acceleration would drop 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 with this .

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

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

Effect: Normal driving is possible as long as you stay within the range where boost pressure properly engages 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 to record the signals would be using VAG-COM.
For the LMM (likely referring to a Lambda Sensor or Oxygen Sensor), I recommend performing a diode test *before* purchasing a new one.

garth.brooks wrote:

Hi, ich hatte genau den gleichen Effekt : Ursache war ein eine offene Lötstelle in der testweise schlampig zusammengelöteten OP-Schaltung für die Ladedruckanhebung/steuerung.

Hi Garth,

Which component are you referring to here?
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 I imagine, lower at partial load due to the reduced exhaust backpressure, and higher at full load because of the visible fuel in the exhaust = soot. And there's a function that makes the engine control unit display 1.4 bar again when it reaches 1.3-1.4 bar, so that it returns to that value faster, but this tends to cause surging – I'm not finished with it yet, which is why I'm tinkering with it.'

I also need the elevation for the gas injection; 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:

ne Fake Elektronik die den Ladedruck so steuert wie ich es mir einbilde, niedriger bei Teillast wegen dem niedrigeren Abgasgegendruck und höher bei Vollast wegen dem sichtbaren Kraftstoff im Abgas = Ruß & ne Funktion die bei 1,3-1,4 Bar der Motorelektronik wieder 1,4 Bar vorspiegelt damit er schneller zurückfährt, aber das neigt sehr zum Pumpen - bin noch nicht fertig damit, deshalb das Gebastel.

Hi Garth,

That sounds interesting.

Is the control unit located within the sensor loop (i.e., a type of boost pressure controller), or is it more likely 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 like I want it to yet, so I don't want to write too much about what's not functioning properly. I've been working on it for a while now, but the weather is too cold for tinkering, and my wife wants a new nest and has given me plenty of tasks to do.

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 this results in incredibly responsive behavior, it also leads to increased exhaust backpressure, which ultimately increases fuel consumption. 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.