Quote:
Originally Posted by funola
The square wave is driving the tach. I soldered a wire onto pin 25 of the EGR computer internally, drilled a hole and brought it out of the box and captured that trace while the engine was idling with the tach registering.
That is actually a very pure sine wave from the VR sensor. Not sure why you call it a psuedo sine wave? What you see on right portion of the trace is shifting frequency, i.e the idle is not perfectly stable but varying, that is what you are seeing on right portion of the trace with muti waves. The engine was cold when the measurement was made. After it is fully warmed up, idle may smooth out and the trace may be more stable- but I won't know for sure till I try it.
What is that 4 wheel trigger wheel from? Don't tell me it is what the VR sensor is picking up in the 85 300D.  |
I called it a pseudo-sine wave because a VR signal should look like this. (although this is running with reverse polarity from "normal" as it shows a rising edge) There is normally a distinct rising voltage, then a near instantaneous drop to negative. This is what makes it so good for timing as you get a very distinct point where the voltage changes.
As the teeth get closer together (as in the MB flywheel) the falling edge gets less distinct as the following image shows, so much so that if the polarity is reversed, it's difficult to tell what is the rising edge and falling edge. (Note the trace is from a timing wheel, like perhaps an EDIS, where the anomaly is from a missing tooth that marks the beginning of each revolution) Someone could easily mistake the trace as a sine wave, when it is in reality not.
The 4-tooth trigger wheel image is from a 722.3x transmission. It's used as a trigger for the speedometer VR sensor.
I don't own a scope, so everything I've shown is from the internet.