Cylinder Volume Difference: Analysis & Optimization

Hello fellow enthusiasts,

I've been wondering for a while how the engine control unit (ECU) detects weaker and stronger cylinders and then adjusts the fuel injection accordingly. What measurement parameters are relevant for this? I'm not entirely clear on how it works.

In short:

The crankshaft speed is measured. The engine control unit (ECU) knows which cylinders are currently firing.

For example, if a cylinder's crankshaft speed increases slightly after the fuel is ignited, the corresponding cylinder is adjusted to reduce its output.

Ah, I understand. Thank you!

'The older' TDI engines had 4 markings per revolution on the crankshaft position sensor (one for each ignition top dead center). (PD engines have a 60-2 sensor).

The EDC is now trying to maintain a constant time interval between the injection pulses, meaning it adjusts the cylinder power so that all cylinders have the same output. These are the values that you can read out in the idle speed control.

'With the VP-37 engines, this is only relevant at idle. At higher speeds, the control system is too slow to compensate for individual cylinder imbalances (although it is still possible to measure and display the deviation).'

For VP-30 and VP-44 models, this also applies in the mid-speed range.
Of course, with PD.

This is mainly for comfort reasons, as 'idle jerk' is a term .

By the way, this whole story takes up a significant amount of space in the EDC software!

CU Gremlin.

@Gremlin
What is an "old" TDI?
Does my mass airflow sensor (MAF sensor) - 1Z - count as well?
At the very least, no disturbance rejection parameters can be obtained. Group 0 doesn't offer much anyway.

'Older' TDI engines are TDI engines that use an injection pump.

Best regards, WarLord.

Hello, what causes a cylinder to be stronger or weaker? In my case, VAG-COM sometimes shows +4.5 mg/stroke. That's quite a lot, and the car is having trouble starting. However, the compression should actually be okay. What else could cause these differences, such as worn injectors or a pump?
best regards, harri

My VAG COM sometimes shows +4.5mg/stroke. That's quite a lot, and the car is having trouble starting. The compression should actually be okay. What else could cause these differences, such as worn injectors or a pump?


The answer suggestions you already mentioned...

4.5 mg/R is not a little, but far too much! (Normal range: -2 to +2).

Causes:
- worn nozzles (most of the time)
- poor compression (rarely)
- ESP (even rarer)

Since you know where to look, get to work.

Best regards, Georg.

Hello everyone,

I'm experiencing a similar problem with my AFB (6-cylinder VP44).
BUT in my case, one cylinder is deviating by a negative amount, not a positive one! I don't know exactly which cylinder it is, which is actually irrelevant... this one is giving me a value of around -2.5mg.
How can this be interpreted? All the other values fluctuate around a maximum of +/- 0.5mg. Are the other nozzles all that bad, or is this cylinder simply inherently that strong?

Regards,

DENNIS

Hello.

GarfieldMZ wrote:

Hello everyone, I'm experiencing a similar problem with my AFB (6-cylinder VP44). BUT in my case, one cylinder is deviating by a negative amount, not a positive one! I don't know exactly which cylinder it is, which is actually irrelevant... this one is giving me a value of around -2.5mg. How can this be interpreted? All the other values fluctuate around a maximum of +/- 0.5mg. Are the other nozzles all that bad, or is this cylinder simply inherently that strong? Regards, DENNIS

Cylinders with a negative mass difference contribute more to the driving force. This indicates that either the reference cylinder is weaker, or the nozzle of the 'better' cylinder is dripping.

Best regards, Rainer.