Erratic TDI | Posts 16+

Hello Bully,

The shaking is gone when the speed sensor is disconnected, but the shifting vibration that Rainer describes is a one-time occurrence when accelerating, and it occurs (or happens smoothly) when the speed sensor is disconnected. If the shaking is gone in the described operating range, then the fuel pump should be defective.
A worn-out control valve does NOT mean a new ESP, but why replace the control valve (which costs more than half of a new pump) if the rest of the pump is also old? Next, you'll need to replace the feed piston, and then you can also replace the pump lower part.

Hello Bertil,

thank you for the explanation. But I don't quite understand it yet.
If I disconnect the speed sensor, and the shaking stops.
then the speed sensor must be faulty, not the pump or?
I currently don't have a speed sensor issue, but I'm experiencing this with the speed sensor disconnected?

Bully

Hello Bully,

The transition occurs when the speed sensor is disconnected, as the STG (control unit) cannot dampen the acceleration, and the thrust cutoff is no longer active.
Regarding "not experiencing jerky movements" without the speed sensor, I cannot provide a logical explanation. I took these procedures with me to the Bosch service, but no one there could explain them to me ("...that's just an experience..." - and that could actually be true, because it was the case with one of our company vehicles).
In the old forum, we had already discussed this and hadn't found a definitive explanation (regarding whether the regulator is easy or difficult to operate?). The idea was then: it is a regulatory swing that is influenced by the interaction between the STG (Specific Target Group) and the regulator. When the speed signal is disconnected, this control loop is likely disabled.

Hello Bertil,

Thank you for the explanation.
Let's see if I've got this now.
Disconnect the speed sensor, then drive. If the rattling disappears when driving at a constant speed, then the pump is defective.
Do I understand now?

Bully

Hello Bully,

exactly like that.

Enjoy trying it out and hopefully it's not the pump!!

Hello Bertil,

I tried to disconnect the speed sensor yesterday,
but I found it somewhere else, but not in the gearbox
Reverse gear lever is there, but the speed sensor – I have no idea where that thing is. There aren't many others left to take advantage of.

Best regards,
Bully

Hello,

It's located on the right side of my A3, in the direction of travel, near the differential (above the connection of the right drive shaft). Maybe this will help you.

Hello, Rainer

Hello,

I also have one of those (BJ 4/94) and I've had some pretty funny experiences. So, your 94 Passat definitely has the 'new' pump with HDK sensor and no potentiometer anymore. Also, you won't find a speed sensor on the gearbox if you have a mechanical tachometer. Instead, there's a speed sensor on the gearbox (but on the engine side). You can also try removing it and driving without it. Unfortunately, you'll have to remove the front engine mount when replacing it :(. Have you had the error memory read out? Check the hose from the intake manifold to the turbocharger for leaks and proper sealing (if there's oil in it, it might be acting strangely), try driving without the valve for the boost pressure regulation (disconnect it) / at the fuel injector wall on the upper right. Schematic available here: dieselkraft.free.fr

If you have any questions, please email dieselkraft@free.fr