AFN Issues: 2300-3000 RPM Problem Explained

Hello everyone!!!

Okay, so I have a 3er Golf GTI TDI with engine code AFN, manufactured in 1996, with 102,000 kilometers on the odometer.
The other two are also 1996 models, and one is a 1997 model with 90,000 km and 115,000 km respectively. Mine has a chip tuning kit installed for the last 60,000 km, while the others are completely stock.
A week ago, I test drove a 1997 model with 90,000 kilometers on the odometer.
"And pikerl (a type of pickled vegetable) with us too... When I tried to raise the engine's oil temperature from 78 degrees to 80 degrees, it started... I kept the engine between 2300 and 3000 RPM, trying to maintain a constant 2400 RPM, and after about 1 minute, it started smoking heavily, blue smoke, no oil... It was unburned fuel that was really burning, like an old, cold truck after a cold start... It's only happening when the engine is stationary, not while driving... I experienced the same thing with my own car, but only at around 70-80 degrees... When my engine is fully warmed up, around 90 degrees, there's nothing after 2 minutes... I also tried the third cylinder, and it's the same there, even with a warm engine... The engine temperature sensors are okay, and there's nothing in the error memory... I used normal diesel fuel... It could just be that the injectors are worn out... Hmm, I would appreciate any help."
"Maybe you could try this on your own cars to see if they also start smoking around 70-80 degrees Celsius water temperature and 2300-3000 RPM when idling. In my case, it started smoking after about 40 seconds at 2400 RPM. Thank you in advance! I would also appreciate a call if you try it: +436642132605 (A1)."

Hi Florian,

I remember similar occurrences when I tapped into the wiring of the speed sensor and the timing sensor to check the tachometer display using a frequency counter. Perhaps the problem lies within the timing sensor itself.

What surprises me, however, is that it's happening simultaneously in all three of your cars - such coincidences shouldn't really occur.

Hello.


Yes, I thought so too... that's why I'll try it on the next ones as well... yes, an OT (output transformer) is a good tip... I'll take a look at it with an oscilloscope, maybe I'll notice something... yes, it was the same for all three... I know my car, but I've never noticed this before... really? Could you try that on yours...?
"Thank you."

I've observed the same problem on my AFN, but I haven't found a solution yet either.

Actually, everything is fine, but it only exhibits this behavior when idling.

Hello everyone.

It is possible that the "quantity setting" mechanism is, due to its design, entering into resonance. This could explain the relatively large number of affected motors without any other errors occurring.

In the pump, we have a fundamentally oscillating system: inertial masses in the form of moving parts of the flow control mechanism, and return springs.

Within the system, the inertial masses are held in a state of equilibrium by a balance between the force exerted by the electromagnet and the force of the return springs.
If motor vibrations affect eccentric moving masses within the metering unit (e.g., control slide, measuring short-circuit ring, etc.), the system can, at certain excitation frequencies = rotational speeds, enter into torsional oscillations that deflect the control slide away from its setpoint = injection quantity.
The amount of fuel injected would be decreased and increased so rapidly that no fluctuation in the engine speed would be noticeable – the effect being similar to a wildly fluctuating idle speed control.

As a result, the EDC constantly receives RWG signals that deviate from the setpoint and adjusts the flow control valve accordingly using corresponding correction signals.
However, since corrections always occur later than the actual error, the oscillations (at a suitable frequency and response time) can be amplified rather than dampened by the correction attempts.
The effect may be further amplified by precisely matched control clock frequencies of the switchgear.
Overall, it appears that the maximum increase in injection quantity even exceeds the soot limit.

The occurrence of torsional vibrations would likely be favored by axial play in the switch machine shaft, possibly due to wear and tear resulting from high operating cycles.

I suspect that these affected engines experience resonance-related phenomena (GAUs) that, fortunately, appear to be limited to narrow speed ranges and "unusual" operating conditions.

It's possible that corresponding fluctuations in the RWG voltage could be read out using VAGCOM during the vibrations. However, since the transmission frequency is significantly lower than the presumed vibration frequency, I doubt this is likely.

A possible solution would be to increase the damping of the system, for example, by installing a vertical damping plate on the outside of the measurement short-circuit ring. This plate would stir the surrounding fuel with every movement of the flow control valve, thereby increasing frictional losses, which could potentially prevent the occurrence of the suspected resonances.
However, I believe that a constructively safe implementation of this idea would involve a significant amount of effort: how can we ensure that parts don't eventually break off due to vibrations and block the signaling system?

My conclusion: Accept it as a minor quirk as long as the engine otherwise runs normally.

Since it only occurs in unusual operating conditions, I'm quite calm about it now.

Perhaps this knowledge will help to lower the price when making the next AFN purchase.

For reassurance. I also have this problem. I had quite a few complications when buying the vehicle and problems with the seller. This heavy smoke formation can also be provoked while driving, but as I said, only within this temperature range, which thankfully is only present for a short time. When driving in 4th gear at this temperature, downshift relatively abruptly, let the engine speed decrease on its own, and check the rearview mirror. It's not a pretty sight . A friend of mine said that it's a problem caused by slight oil overfilling, as a certain amount gets into the intake manifold and accumulates there, but that's illogical again due to the temperature dependence. In addition, at the exact engine speed where the smoke occurs, the engine starts to vibrate very strongly, which supports Ulf's theory. The vibrations are noticeable throughout the entire body.