AFN Wiring Harness Pinout T68 Connector

"I've been driving a Passat with an AFN engine in my 'T3' van for a few years. Now, it's not running as it should. The error memory shows no messages. When troubleshooting, it was found that the supply voltage for N109 (fuel cut-off) is sometimes present and sometimes not. However, the wiring harness shows no loose connections. When the engine is running, it only sputters with a lot of smoke, and it only runs 'smoother' at higher RPMs. While checking and comparing possible wiring diagrams and wiring harnesses, I noticed that in my configuration, the connection from T68/51 to N109 (fuel cut-off) and T68/53 to N108 (fuel injection start) is wired as such, but in all other wiring diagrams, it's the opposite. Is this okay, or do I need to change something? As I said, it has been running perfectly fine until now."
Sure, here's the translation:

"Thanks in advance, and best regards."
Hartmut.

Hi,

Have you replaced the relay 109 yet? There are certain production batches that have a high rejection rate and cause the most peculiar errors.

Best regards,

Jan.

hammuts wrote:

While checking and comparing the possible wiring diagrams and cable harnesses, I noticed that in my specific configuration, the connection of T68/51 is to N109 (fuel cut-off), and T68/53 is to N108 (fuel injection start), but in all other wiring diagrams, it is exactly the opposite. Is this okay as is, or do I need to change something? As I said, so far it has been running perfectly.

Hello Hartmut,

Normally, the fuel shut-off valve (N109) is connected to 12 volts via terminal T68/53, and the fuel injector control valve (N108) is connected to ground via terminal T68/51 (in this state, both components are energized).

If the wires are swapped, I highly doubt that there's a sufficiently low-resistance current path within the engine control unit (it would have to be some kind of symmetrical output stage or something) to provide enough power to these types of consumers. Furthermore, the fuel injector output operates with pulsed voltages, which the shut-off device probably wouldn't be able to handle effectively.

I suspect that the engine wouldn't run at all with the swapped wiring.

I agree. My problem is just how to deal with this inconsistency!
Should I take the wiring harness and dashboard from a Golf III?
So far, I've been doing things this way, and at least the wiring diagram for the Passat is consistent with the wiring harness.

Regards,
Hartmut.

hammuts wrote:

Should I take the wiring harness and cables from a Golf III?

Hi Hartmut,

If the engine computer is also from the G3 -> yes.

Hello Hartmut,

Okay, I'm going to carefully check exactly what parts I have. Based on the VW part number, your local VW dealer can tell you which vehicle the control unit came from. There's also a production date listed on it. As far as I know, the wiring harness for the Passat has a different color coding than the one for the Golf, specifically the Audi color coding, at least if it's the Passat with the longitudinal engine. Then, I would get the exact wiring diagram that applies to me and connect everything as described in it, even if it means swapping those two wires. I'd do that out of pure curiosity to see what happens.

Hello.
Wolfgang.

Control N109/N108.

Hello Wolfgang.

In this wiring diagram for AFN engines with manual transmissions, version 10/96, issue 01.97, the N109 (cutoff valve) is supplied by the control unit via connector T68/51, and the N108 (fuel injection start valve) via connector T68/53. In all other wiring diagrams I am familiar with, it is the opposite. When checking the original corresponding wiring harness, the wire connection between T68 and T3 does indeed correspond to this wiring diagram, but surprisingly, the wire color is reversed! This is not a mistake, but an original VAG specification.
Does anyone have an explanation for this?

Thank you and.
Regards,
Hartmut.

Hello Hartmut,

That looks very much like a printing error in your circuit diagram. Do you have the original VW documentation? Unfortunately, those are not always perfect either; I've found a few errors myself, although not in such a critical location.
I can send you the wiring diagram for the Passat AFN, starting from October 1996, issue 4/98, if you give me your email address, as it's corrected in that version! Please also check the number in the drawing, in the rectangular box in the bottom right corner; mine says 97-22788.

Do you have to swap your cables now? That would be quite something...

Hello.
Wolfgang.