Engine Misfire: Short Noise When Releasing Gas

Hi everyone,

"A recurring problem has surfaced again in my car: When releasing the accelerator and disengaging the clutch after high engine load at low RPM (up to approximately 1800 rpm), I hear 2 to 3 brief, intermittent grinding noises (?), seemingly coming from the area of the turbocharger, for about 0.5 seconds."
The boost pressure indicator drops abruptly in steps, decreasing from approximately 0.8 to around 0 bar.

What's strange is that the gauge seems to almost freeze for fractions of a second several times, as if someone were squeezing the hose to the intake manifold and briefly "trapping" the pressure in the gauge.

When releasing the accelerator without depressing the clutch (i.e., when the engine speed doesn't drop), the effect is surprisingly not noticeable.
It probably has nothing to do with the large container, because it has also happened occasionally with the smaller one.
All the other functions of the charger are still working perfectly normally.

After the initial shock a few months ago, I removed the suction inlet from the charger and fiddled with the turbine, trying to see if anything was rubbing. The shaft had some axial play and could be tilted by about 1mm, but I couldn't find anywhere where it was rubbing.

Does anyone have any idea what this could be?

Hi Ulf!

If you describe it in this way, it might possibly be related to that.
I think that when the loader is under load, the play won't be as noticeable as when you release the accelerator and the loader returns to a speed range where this play becomes more problematic.
Simply test it out! Grab a second person and tell them to accelerate while you listen!

Hi.

Quote:

Just test it out! Grab a second person and tell them to rev the engine while you listen!

This is probably not so simple: the EDC apparently detects when there is no load on the engine and, in this case, does not increase the boost pressure (and probably also the fuel injection amount) nearly as much when the vehicle is stationary as it does when it is moving .

Hello Ulf:

Regarding the turbine wheel play: The turbine wheels are relatively loosely mounted, and the turbine shaft itself isn't particularly thick. This play is perfectly normal. As you probably already suspected, the (hopefully non-existent) imbalance is crucial.

I cannot observe the phenomena you described in my car. Perhaps it's an artifact of the VTG control system under certain conditions.

Does anyone know how turbine blades/vanes are manufactured to minimize imbalances?
Just for comparison: In so-called ultracentrifuges with a speed of 60,000 rpm and a radius to the accelerating mass of 1 cm, accelerations of approximately 4 x 10^4 g occur due to the inertial force. A loader, however, rotates at a speed in the range of 120,000 rpm.

Best regards, Georg.

Hi Georg,

Z.B. die Fa. Schlütter überholt Lader einschl. Abalance.

Since they provided me with very helpful advice regarding the larger load capacity, perhaps you could also find out more about the fine-tuning of the running gear.

www.turbocharger.com