1Z engine keeps stalling while driving

Hello everyone!

First, let's talk about the car:

Volkswagen Golf 3, 1.9 TDI, manufactured in 1995, with a 1Z engine.

Mein Problem: Vor einiger Zeit sprang der Motor nicht mehr an. Dabei leuchtete die Vorglühlampe leicht, der Drehzahlmesser rührte sich nicht. Beim Abschaltventil an der Einspritzpumpe kam kein Strom an. Hab hier schon einige Beiträge zu dem Thema gelesen. Hab dann das 109 Relais gemessen und festgestellt, dass es keinen Strom bekommt. Also die Kabel zum Motorsteuergerät gemessen alles ok! AAll other suspect cables were measured as well, and everything is okay.

My suspicion was that the engine control unit (ECU) was defective. I then intended to get a new ECU from a car recycling center. Unfortunately, they only had ECUs where the last two letters of the Bosch part number didn't match. Since I once heard that these letters only indicate the software version, I gave in and bought one of those ECUs with the mismatched letters.
I installed it, and I was very happy because the car started up immediately and ran well. However, after about half an hour of driving, it simply stopped. On the first attempt to restart, it did the same thing as before the troubleshooting. The only difference is that the glow plug light is now shining brightly instead of dimly. The second time, it started right away. To further narrow down the problem, I need your help.

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

"Some questions:"

1) What is the actual meaning of the last two characters in the part number? Could it be that these characters cause intermittent problems with the immobilizer system? (I thought that if the engine control unit doesn't work properly with the immobilizer, the car generally won't start at all.)

2) Or can I assume that the problem is not coming from the control unit and should instead be investigated towards the ignition switch and immobilizer system?

So, generally speaking, would you assume that I need a control unit with a perfectly matching part number, or is it more likely that this error is caused by other factors?

Best regards and thank you in advance.

Tobi.

We need ZDF (Numbers, Data, Facts) in order to be able to help you specifically. So, please provide the last letters of the two M-STGs . Is one of them a completely metal-cased unit, or is it an older one with a plastic casing (MSA12)?

If the WFS (Window Film Sensor) were faulty, the engine would start but stall after 1 second. So, that's not the issue in your case. However, this car should have had a WFS installed since 1995 (or possibly from 1994, if I remember correctly). It's possible you bought an older MSG (Motor Steuergerät - Engine Control Unit) that doesn't require a WFS, which is why it's working.

The letters on the MSG indicate both the hardware version and the software. For example, you might have installed an MSG intended for a different engine (e.g., AFN). This sometimes works, but certain parameters may not be as optimal for your 1Z engine.

Despite that, I can't think of any reason why your engine should shut off after half an hour and then fail to restart, and how that would be directly related to the MSG (Main System Module). I suspect it's more likely a problem with the power supply or wiring.

For me, the central point of investigation would be the ignition switch. Has smoke ever come out of it? That's what happened with my Golf 3...

Greetings.
Sure.

Here is the translation of the text from German to English:

"Guste" means "gust" in English. It refers to a sudden and strong gust of wind.

Okay, thank you! Those are very helpful suggestions. I won't have the final characters until tonight. But I already know that my "new" control unit has a plastic housing, while the original one had a metal housing. However, I was lucky enough to get at least the MSG (Message Interface) from a 1Z model. So, the parameters should be correct, right?

I also think that the focus should be on the power supply. I will start by looking at the ignition switch. Can I check or repair it, or should I replace it immediately? It has never been used before. [/b]