TDI Engine Problems: Golf III Won't Start?

Hello, I'm not sure if I'm in the right place, and I don't know if anyone here can answer my question.

I have a Golf 1.9 TDI with engine control unit 028 906 021 AF (07.02.95). The housing is black and silver. I wanted to replace this control unit with another one, 028 906 021 BF (07.05.96), which has been tuned and has a completely silver housing. Unfortunately, the engine doesn't run with this new control unit.

The old control unit still has the two rectangular chips soldered in, each with 14 pins on each side, while the "Tuing" control unit has the square chips with pins on all four sides.

My question is: Can these control units generally not be swapped with each other, or could it be because the tuning control unit still contains an immobilizer? What can I do in that case?

I can only phrase it like this; unfortunately, I'm not more familiar with the details.

Best regards,
floreal

The immobilizer must be adjusted in any case!

I don't know if the two mentioned items are compatible with each other. As a third possibility, you should consider that the control unit (STG) might be defective, which depends on where you bought it from (e.g., eBay?).

Best regards, Alex.

The old one doesn't have WFS, and I'm not aware if the new one does. If it's related, can they disable the WFS in the new one at the VW dealership?

"If so, does it work when fully assembled? (The installation itself wouldn't be a problem on-site, but I'm just not sure if there's a number on the control unit that indicates whether it's with or without WFS?)"

021AF and 021BF are interchangeable without any issues.
Otherwise, as Alex already wrote: WFS needs to be adjusted;
However, the car should still start and run for approximately 1 second even without the modification with the new control unit.

Best regards,
Rudi

"Yes, that's right, it turns on for a second and then turns off...is that a good sign? And can VW possibly help me with this? What information do they need?"

The old one does NOT have WFS, and I am not aware if the new one does. If it is related, can they disable the WFS in the new one at VW???
If it's a 021AF, it has a WFS (at least, I haven't encountered one without it yet).
The 021BF definitely has one.
Disabling WFS... ... is (theoretically) possible, but VW cannot and will not do it.
they are also guaranteed not to do that (more likely, they will call race control and hand you over to their care).

Best regards,
Rudi

..Yes, that's right, it turns on for a second and then turns off...is that a good sign...? And can they possibly help me at VW...? What information do they need from me?
Positive (MSTG is alive).
VW can only adjust the WFS (Workforce Management System) for you (or you can use/borrow/buy a VAG-COM device).
and make it yourself).

Best regards,
Rudi

Instructions on this topic are NOT available in this forum!

Best regards, Alex.

"Yes, you're right, deactivating it would probably be illegal. Does anyone know how much something like that might cost at VW, and how long it would take?"

...yes, that's right, deactivating it would probably be illegal...does anyone know how much something like that might cost at VW and how long it would take?
I would say, off the top of my head, 25 euros for 3 minutes.
It's best to go to a trusted mechanic and have them check to see if there's anything wrong with your car.
It actually has a WFS, and I'll also handle adjusting the WFS settings.
If that's the case (which I assume it is), you'll change the MSTG on the farm and have it adjusted.

Or you could ask in this forum if anyone lives near you who has a VAG-COM device.

Best regards,
Rudi

Hello again.

I would like to sincerely thank Rudi and majesty78. Your quick responses were very helpful to me. Today, I went to VW, where I had to present my vehicle registration document and my ID. Then, the "new" engine control unit was connected online to VW and adapted to my keys (WFS). So, even the spare key that I didn't have with me still works, and the whole thing cost a reasonable 16 euros!

Der Golf läuft nun tip top, nicht zuletzt machen die 29PS und 70 Nm Mehrleistung auch viel Spaß (Endgeschwindigkeit ist auch um ca. 10-15 KM/h gestiegen (lt. TI think.

Best regards,
floreal

Great. Thanks for the feedback.

Best regards,
Rudi