Increased AFN: Strong Vibration and Shaking

Hello, fellow diesel enthusiasts!

I'm having a problem with my car. It's a 1997 Volkswagen Golf 3 AFN with a chip tuning upgrade from Tuneline (145 hp / 305 Nm).
Current mileage: 107,000 (chip installed at 70,000).
'Without using the performance boost, everything works fine (at least for now). But as soon as I engage the performance boost and accelerate to full throttle, there are very strong vibrations and a wild shaking felt within the RPM range of 2000-2500. This is accompanied by a very deep, rumbling sound. It's noticeable starting in third gear. The higher the gear, the longer the vibration phase, as the engine stays in that RPM range for longer. This phenomenon has only been occurring for about half a year, so it wasn't always like this. Could it be that the clutch is worn to the point where it doesn't fully engage in this RPM range, where the torque is highest? Or could it be related to the engine itself?'

I would be very grateful for some feedback.

Thank you in advance for your help.

Best regards,
Thomas

Hello,

If your problem started at the same time as the performance upgrade was installed, I am aware of that. Unfortunately, I haven't yet figured out the exact cause.
The speculations ranged from resonances in the intake manifold, transmission, engine mounts, etc.
Right now, the engine mounts seem most likely to be the cause. Theoretically, the increased torque could cause the engine to tilt so severely that something mechanical could collide.
Check the engine mounts.

Best regards, Rainer.

Hello Rainer!

Thank you for the quick response.
Unfortunately, these vibrations only started appearing a year after the performance upgrade. Everything had been working perfectly fine before that. I'll still check the motor bearings just to be sure.

Best regards,
Thomas

This phenomenon occurs in all 'heavily' modified Golf III TDI models! The vibrations come from the dual-mass flywheel, which rotates to its extreme limit and thus becomes unbalanced! I was able to eliminate this in my car by installing a VR6 flywheel and the corresponding clutch.

Best regards, Holger.

That's interesting... I've asked that question before too.

We had my car on the lift this weekend specifically to investigate this issue, and we thoroughly checked everything for any signs of mechanical contact. We even tested it while operating it (with someone inside, rapidly engaging and disengaging the clutch and brakes) – but unfortunately, we couldn't find any evidence of any contact.

However, I have the flywheel from the G60 installed - it shouldn't differ significantly from the one for the VR, should it? Does anyone know more about this?

To make matters even worse for me, I have the G60 engine mounts installed – because the TDI mounts didn't fit the axle. Many people have already spent a lot of time trying to figure out the cause of the vibrations, and so far, everyone has concluded that the G60 flywheel is the culprit.

arne

Hi!

I have an AHF and an AJM, both with chip tuning. These vibrations occur in both vehicles.
The fact that you only recently noticed this effect is likely due to the outside temperature. I only experience these vibrations when the temperature is below approximately 7 degrees Celsius. However, the engine produces more torque at lower temperatures. This seems to be the reason for the different behavior at various temperatures. More torque equals more vibrations.
Unfortunately, I don't know any more about the cause.

Best regards,
Uwe

Hello.

I installed an AHF (air heater) from a 1998 Bora in my VW T3, and I'm experiencing the same problems with the excessive roaring and vibrations.
The rumbling noise occurs under load between 3000 - 3900 RPM and then disappears as if it's switched off. It also occurs when I release the accelerator and use engine braking in that RPM range.
Here's what I've already done to try and figure out the cause.

- Exhaust pipe detached from the turbo and driven without it ---- No change.
- Air filter removed, no hazards detected.
- No change.
-Air intake modified and insulated----------------Slight improvement in droning noise.
- Rubber engine mounts replaced with hydraulic mounts -------- No change.
-Gearbox mounting placed on rubber pads----------------------No change.
- Removed the engine mounts and suspended the engine in the engine bay using ropes and a support.
----------------Slight improvement in the rumbling noise.
Engine bay insulation improved - noticeable reduction in engine noise.
ZMS (dual-mass flywheel) with disc and automatic transmission removed and replaced with a conventional clutch from a 1.6 TD Golf. -----------------------------------Slightly reduced noise (but the clutch is very light ).

What about the crankshaft? Should it be finely balanced with the vibration damper? Does anyone have experience with this? What else could be causing the vibrations?