Starter Ring Gear: No Missing Teeth?

Hello everyone,

I want to determine the motor speed by tapping into the G28 inductive sensor using a parallel connection.
While measuring the gear, I noticed the following:

The missing tooth (or teeth) required for Optical Transduction (OT) recognition is not present on my ASV (presumably referring to a device or system).
The inspection was carried out using an Ozi.

Now I have two questions:

First of all:
It is now very difficult (actually, not possible ) to count the number of teeth on the starter ring gear. Who knows how many teeth the starter ring gear has? 30 or 60?

Secondly:
Does the OT (Over Torque) detection not require a control unit for the VP 37 pump, because there is a fixed relationship between the engine speed and the injection pump speed?
According to the wiring diagram or MSG configuration, there is no dedicated crankshaft position sensor (e.g., on the camshaft).


Thank you for any assistance you can provide.

Best regards, Jochen.

Hi Jochen,

As far as I can remember, the DZ (dwell) signal for the G28 on the 028/038 VP engines is not taken from the starter ring gear, but from the 4 markings on the crankshaft/flywheel. This automatically also provides the top dead center (TDC) position.
"You never really measure anything on the starter ring gear, do you? You probably mean the commonly used 60-2 or 60-2-2 or 60-2-2-2 sensor wheels found on modern engines (for electronic timing)."
Measuring the speed of a 60-2 wheel using a tachometer is also technically challenging. You need a sampling rate of almost 15,000 Hz to evaluate the teeth, and you also need additional logic to compensate for any missing teeth.

Alternatively, you can simply take the NBF signal and calculate the DZ (distance to zero) from it. This is the easiest method, and it's what the EDC (Electronic Distance Measurement) system does anyway in case of a G28 failure.

Best regards,

Here's a little thought starter. Previously, the signal was tapped at the Lima using the existing terminal W. This works similarly if you solder a wire to the windings. Try it in a discreet location; it might help.

Hello Bafische,

Hi Jochen,

As far as I can remember, the DZ (dwell) signal for the G28 on the 028/038 VP engines is not taken from the starter ring gear, but from the 4 markings on the crankshaft/flywheel. This automatically also provides the Top Dead Center (TDC) signal.


Great, that's a good starting point that I can work with.
As I now understand and have measured, the signal has the same markings. Therefore, if I include the NBF, I only have the OT marking, correct?
This isn't so important for my current measurement, as I want to capture the absolute rotational speed.


'You never really measure anything on the starter ring gear, do you? You probably mean the commonly used 60-2 or 60-2-2 or 60-2-2-2 toothed wheels used in modern engines (for electronic timing).'
Measuring the speed of a 60-2 wheel using a tachometer is also technically challenging. You need a sampling rate of almost 15,000 Hz to evaluate the teeth, and you also need additional logic to compensate for any missing teeth.


Yes, you are right.
I mistakenly assumed the starter ring gear was the trigger point because we have MRS sensors applied there. However, these sensors only captured the speed and direction of rotation. We previously determined and calculated the top dead center (TDC) position.
I understand that measuring the speed can be technically challenging, but that's precisely the approach I'm taking with my measurement.
The measurement is intended for validating measurement technology. Therefore, your [something is omitted here].
and the alternatives proposed by Mullemaus.

But thank you very much for your help, I will measure it right away.

Best regards, Jochen.

Jochen_145 wrote:

Since the signal, as I now understand and have measured, has the same markings, I only have the OT marking now, if I include the NBF, or ?

I don't believe that; the engine runs even without the NBF. That proves that the timing signal is obtained from somewhere else.

Okay, the speed measurement is running.

Bafische was correct with his 4 markings on the encoder disc. I can now measure the motor speed using a parallel connection to the G28 sensor.

@Wolfi_b,

If the engine also runs without the NBF (presumably a specific component), then my assumption above might be correct.

The VP 37 (and other VP pumps) have a rigid, mechanical connection between the crankshaft and the injection pump, which is achieved using a timing belt.
Therefore, the basic injection point is fixed. I do not need an OT sensor. By shifting the injection timing, I can relatively change the actual injection timing with respect to the basic timing.

The older distributor ignition system with a breaker contact, commonly found in gasoline engines, is similar in that it is also rigidly connected to the crankshaft (via a timing belt, chain, or sprocket) and therefore does not require a crankshaft position sensor.

Best regards, Jochen.