CKP Waveform Questions

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6 years 3 weeks ago - 6 years 3 weeks ago #18443 by rockp2
Folks, I have a couple questions about the attached waveform. I am playing with my tools and building my own waveform library of known goods. This is from a 98 Chevy Blazer vin "W" 4.3L engine DI igntion. The CKP sends a 3x signal to the VCM. The conditions:

-Engine is at idle 650 RPM
-Closed Loop
-Cam retard 0
-Coolant 188F
-Scope is a Vantage Pro hooked up with lead backprobed into 3x signal wire, ground lead connected to B-, for the attached image I had Peak Detect "ON". I meant to also have an image with Peak Detect "OFF", but somehow I managed to lose the file while transferring to my puter. Suffice it to say, it looked exactly the same but without the little warble at the end of each "OFF" signal.
-This is a pull up circuit with power coming from a fuse in the UBEC

My first question is concerning the voltage. I was really surprised to see the CKP produces such a high voltage signal. I had a looked around on IATN before I did this and I couldn't find a known good for my truck. I found one for another year, but I couldn't see exactly what the voltage was because there was not a scale. I also found an old post where guys were discussing a bad CKP that had been replaced with a new sensor that only went to ~10V and apparently fixed their issue. But my voltage was hovering around a 13V signal. The truck runs well, with no codes or problems. So is the signal I am showing in the waveform good to go? Peak-to-Peak was -0.44V to 13.11V.

My second question is concerning that warble at the end of the "OFF" signal, is that normal? Is that because the tooth on the tone ring was approaching and the magnetic field was getting ready to close? Or is there something wrong there? Once again, with Peak Detect off, there was no warble at all.

Would you say that I can call this a "Known Good" for my library...or no? Thanks for any knowledge you toss my way!

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Last edit: 6 years 3 weeks ago by rockp2.

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6 years 3 weeks ago #18483 by Landroverman1958
Hiya,what does the vantage pro say in the in the descrption in component tests?does it give an example for the wave pattern?

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6 years 3 weeks ago - 6 years 3 weeks ago #18488 by graywave
Replied by graywave on topic CKP Waveform Questions
That tiny little spikes look like just noise to me, maybe from the ignition system. Peak detect can oversample an area as well. So if that is there with peak detect and gone without peak detect, I wouldn't worry about it. Looks like a "Known Good" to me just ignore the little spike.

As far as System voltage peak, this is normal for many CKP and CMP sensors. I just had to replace a CMP sensor on a Ford 7.3L. with an intermittent stall no start.

Known bad capture. I almost thought that I should see a clean 5v square wave with a good sensor due to the voltages of this capture.
Green - Sensor Ground
Yellow - 5v Ref
Blue - CMP Sig
Capture was taken during cranking which is why the ground is so noisy.


Known good capture. System Voltage. The system voltage was not present at the sensor with KOEO so I thought it was a pull up to 5v design. At some point I want to test for system voltage on the signal wire during cranking. It has to be a pull down design.


Here is a Nissan I did. Known Good Capture also hitting system voltage.

Confirm what it's not, and fix what it is!
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Last edit: 6 years 3 weeks ago by graywave.
The following user(s) said Thank You: rockp2

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6 years 3 weeks ago #18508 by rockp2
Replied by rockp2 on topic CKP Waveform Questions
Landroverman, the Vantage Pro example in the preset showed a squarewave like I had, but without the warble at the end of the "OFF" signal. However, the example did not did not indicate what voltage should be. Note also that the Vpro preset was with Peak Detect off. Based off of Graywave's post and the fact that the truck runs fine, I feel good about calling this a Known Good.

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