Jerking/Stuttering with TD? Who can help?

Hello.


I have a Volkswagen Golf III, manufactured in 1997 (TD), with a 1.9L engine, engine code: AAZ.
I am experiencing the following problems:
My car has a hesitation/misfire at 2,000 RPM. It behaves like this: when I accelerate gently, there's a brief loss of acceleration around 2,000 RPM, followed by a slight jerk, and then it continues (it only lasts for about 1-2 seconds). What I've also observed is that when this error occurs and the car continues to run, a small puff of gray smoke comes out of the exhaust pipe.

Here's the background: My engine was broken (but not for that reason), and I installed a new one. While it was warming up, I noticed that the diesel pump was leaking. So, I had the diesel pump rebuilt and resealed by Bosch, including replacing the part-load regulator. Since then, I've been having this problem. I've been to Bosch five times, and they've adjusted the fuel injection timing and checked other things. After I got a little louder during my fifth visit, they installed the spring package from my old part-load regulator, hoping it would fix the issue. It's gotten better, but it's not completely gone. The Bosch mechanic told me that there was nothing else they could do, and he had also spoken to a Bosch technician. Apparently, with a motor, sometimes it works fine, and other times you can tell something is wrong.

It's also the case that it's a bit worse when the engine is cold!


Well, I don't know, like...? I believe that Bosch Mech. is just trying to deflect blame.

Has anyone ever encountered this kind of error and managed to get it resolved? It would be nice if you could let me know.

(The engine is brand new, with new injectors, a new turbocharger, a VW diesel filter (no air bubbles in the line), new glow plugs, a new coolant thermostat, etc.) All parts have been re-checked by Bosch and are okay!

Hello.

'This is the response I received so far:'



'Der schnelle braune Fuchs springt über den faulen Hund.'
Hi,

I'm just guessing wildly (don't yell at me), but I think that's the ESP! You were able to pinpoint the error so precisely (2000 RPM) that things like water in the air filter or similar jokes are probably not the cause.
I suspect that the ESP pump suddenly stops generating pressure, which is why there's a 1-2 second delay before the motor continues running. Perhaps the exploded diagram of the ESP on Sönkes' website will be helpful. However, if Bosch was involved, they might have messed things up again (sorry). It's unacceptable that they would stand in front of their product and say they know nothing more!
If you want to take a closer look yourself, I would check the ESP (Electronic Stability Program) for any imbalances or cracks, as these could be signs of wear.

'Der schnelle braune Fuchs springt über den faulen Hund.'
Hello,
If your pump has a load-dependent start-up, it's possible that when you're in a partial load range and then accelerate, the injection timing won't adjust quickly enough from late to early (this can cause white smoke, indicating unburned fuel, and a lack of power). Either the injection molding nozzle shut-off plunger is sticking, or there is a fault with the LAFB hydraulic system.
'Der schnelle braune Fuchs springt über den faulen Hund.'
Hello.


'Yes, my fuel pump has an Elk-dependent start of fuel delivery. The car should also be operating in the partial load range because it happens at 2000 RPM. However, it's worse with a cold engine and slightly better with a warm engine. What I don't understand is that the pump was completely disassembled and rebuilt by Bosch, and completely resealed. If the injection control piston was sticking, Bosch should have noticed it and fixed the problem. Unfortunately, the Bosch mechanic didn't mention anything about that. And before the pump repair, the car was running perfectly. The Bosch mechanic said it's due to the partial load regulator and the interaction between the Elk-dependent start of fuel delivery adjuster and the mechanics of the pump.' And he said there's nothing that can be done about it?! I also asked if the engine could break down, and he said NO!
What is LAFB hydraulics?
What is the function of this LAFB hydraulic system?

'Taja, what should I do now?'

Best regards from Mark.
'Der schnelle braune Fuchs springt über den faulen Hund.'
Hello.

And what can I do to fix the problem? Do I need any special tools, and do I need to order any parts? Do you happen to have a repair manual or a diagram?
'Der schnelle braune Fuchs springt über den faulen Hund.'
Hello, Mark,

You can try to discontinue the LAFB.


'Der schnelle braune Fuchs springt über den faulen Hund.'
Hello,

If you temporarily or permanently remove the aLafb or apply http://www.fatty-fuels.de/messages/19638.html2V, you should advance the injection timing. The Golf with aLafb should have 0.8 mm before TDC (Top Dead Center), while the Passat without aLafb should have 0.9 mm before TDC.
aLafb (Load-dependent start of boosting).

Without modification, the ESP will always inject fuel too late, causing the car to run rich, produce some smoke, and lose power.

Despite everything, I would strongly reprimand the Bosch employees beforehand. The excuse that 'this doesn't always apply' is unacceptable. 'That's not a diesel engine; you can feel that kind of shuddering at 2000 RPM.'
I'm just saying, it's cheaper to buy an ESP from eBay than to go to Bosch once.

Bye.
Sönke.
'Der schnelle braune Fuchs springt über den faulen Hund.'
Hi.
Okay, so I'm thinking about trying to disconnect the ALAFB to see what the pump would do in that situation. Whether the car would then run worse or better, or whether anything would actually change at all!
'However, the two cables coming from the ALAFB go to the compact connector, and I don't want to break the connector just to get those two cables out.' Is there another way to test the ALAFB, for example, by measuring something or using a similar method?

What would a new ALAFB cost? Does anyone know the price? If the ALAFB only cost 50€, I would exchange it permanently, hoping that the error would then be resolved.


Does anyone have a spare ALAFB module that I could borrow briefly to swap out and see if that's the cause of the problem?


Best,
Mark
'Der schnelle braune Fuchs springt über den faulen Hund.'



Okay, if anyone has any other ideas, please share them here!


Best regards, Mark.

Hello.

I read the engine control unit today using VAG-VOM.
The following error codes were stored in the memory:


Sure, here is the translation of the text from German to English:

2 errors found:
01050 - Fuel quantity control actuator (V117)
31-10 - Interruption or no interruption. Short circuit to ground - Intermittent.
01204 - Relay for Climatronic (J254)
30-10 - Interruption or no interruption. Short circuit after positive - Intermittent.


I was able to clear the error codes. However, I haven't done a test drive yet after clearing them. Could it be that the car is running better now?
And what do these errors mean?

Regarding error number two, I would like to add that I do not have a Climatronic system.


Thank you, and best regards, Mark.

Hello.

I think I've found the error! X
'Since Bosch and VW are unable to find the error, unfortunately.'

It seems like it's the AGR (Abgasrückführung). I reviewed my old documents again and realized that the AGR system operates mainly under partial load conditions. Therefore, I deactivated the AGR (Acoustic Glide Reduction) system today, and lo and behold, the car runs perfectly! It's smooth, without any jerking or smoke, just great!

I just ordered a new one, and I'm expecting to receive it on Friday, so I'll install it right away.



Okay, so thank you again to everyone who helped me. Best regards from Mark.