Tachometer für Benziner mit TDI Steuergerät

"Hi everyone, I have a small problem. I'm driving a T3 with an AFN engine. The tachometer is original from an MV gasoline model. I've been told that the tachometer from the MV is compatible with the TDI engine control unit (ECU). I've tried everything with pull-up and pull-down resistors, but nothing works. It should work, but something's not right. The ECU outputs 4 square wave pulses. The MV tachometer also has 4 pulses, but are they square waves? I have a friend who told me that he has an MV tachometer connected to his TDI ECU, and I'd like to see it, but he lives 1000 km away from me. I would be grateful for any kind of answer. P.S. I've already searched the forum and tested the tachometer, everything is fine. The tachometer signal from the ECU is also connected. "

I've been researching tachometer modifications for a while, and from my understanding, very, very few tachometers are actually suitable for both gasoline and diesel engines.

In practice, you'll only be able to achieve this with a suitable speedometer.

Ich mein, dass das nur geht, wenn der Tacho original auch schon vom Motorsteuergerät versorgt wurde und der Motor die gleiche Zylinderzahl hat. Beim 35i B4 mit elektronischem Tacho kann man das zumindest machen, da diese Drehzahlmesser direkt vom Motorsteuergerät versorgt werden. Ob das schon beim mechanischen funktioniert? Ka hunch.

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If you get a speedometer from a T4 (the older type), you can also fit one from a Passat 35i. Just check on eBay; you can often find speedometers for gasoline engines and TDI models (though those with MFA are rare, especially for TDI and four-cylinder gasoline engines).

Best regards, WarLord.

Okay, thank you for your answers, but I've already gotten that far. As I mentioned, it works regardless of whether it's a diesel or a gasoline engine. Both engines produce 4 signals per revolution. However, the signal from the gasoline engine is very likely not rectangular . I need an answer from someone who knows what signal the 2.1L gasoline engine produces. I think then we'll know which direction we need to go in.

Hello,

The input and output impedances of the components are not compatible, so the voltage supplied to the tachometer from the engine control unit (ECU) is insufficient! You need to insert a pulse shaper (a Schmitt trigger with a low-impedance output or an impedance converter) in between so that the tachometer displays something.






Best regards, Holger.

Hi Holger, I'm from CLP. What kind of vehicle do you drive? Also a van? It doesn't really matter, but your answer sounds pretty good. So, if I understand correctly, the ECU from the TDI 5V and the one from the gasoline engine both come from the same source, so they should be 12V, right? But what component do I need to connect in between for it to work? And another question: Why does it work for others without all these things?