What is causing all this noise?

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MachOne
Newbie
Posts: 5
Joined: Wed Apr 24, 2019 11:02 pm

What is causing all this noise?

Post by MachOne » Thu May 02, 2019 11:30 pm

Any idea what is causing all this noise in all 3 waveforms? I checked my ground, direct to the battery multiple times and it was good. I was backprobing at the PCM and I believe I had a good connection there as well.

This is a screenshot of the waveform, saved in my google drive. All help greatly appreciated!
https://drive.google.com/file/d/1_jWg5l ... sp=sharing

Alan
Pico Staff Member
Pico Staff Member
Posts: 257
Joined: Thu May 25, 2006 8:02 am

Re: What is causing all this noise?

Post by Alan » Fri May 03, 2019 5:00 am

Although the Pico test leads and the PicoScope itself are screened the wires in the wiring loom of the car itself are not screened (to save cost and weight).

The wires from the cam & crank sensors probably have other noisy signals running alongside them in the loom (ignition and injectors) causing these spikes.

Inside the ECU inputs from sensors are filtered to remove this noise. You can do the same to "clean up" the waveform using the filters built into PicoScope https://www.picoauto.com/library/training/filtering

Often though its best to start with the filters off - sometimes excessive noise can be due to a fault so getting used to what is normal is good experience.

MachOne
Newbie
Posts: 5
Joined: Wed Apr 24, 2019 11:02 pm

Re: What is causing all this noise?

Post by MachOne » Fri May 03, 2019 10:19 am

Thank you.

MachOne
Newbie
Posts: 5
Joined: Wed Apr 24, 2019 11:02 pm

Re: What is causing all this noise?

Post by MachOne » Sun May 05, 2019 9:07 pm

Can we go a little more in depth?

Background. Vehicle came in with intermittent no start. P0339 Intermittent crank signal

I wanted to play with the scope.

Hooked it up. Now when the car was running well, I got all this noise, BUT, when the car began to run like shit, and the CKP began to break down on the scope, the noise disappeared from all 3 channels!

So was the CKP the cause of the noise all along?

Here again is a screenshot, stored on my Google Drive. https://drive.google.com/file/d/1G-LQQh ... sp=sharing

And here are the 2 waveforms, so you can open then up yourself
This first one is with no CKP breakdown, and noise. My foot is on the gas pegged at the neutral rev limiter (about 3500rpm)
https://drive.google.com/file/d/10eJwUv ... sp=sharing
And this second where is where the CKP is breaking down, Again at 3500rpm to induce the breakdown.
https://drive.google.com/file/d/14uMQOB ... sp=sharing
The result of the CKP breakdown is the engine falling on it's face, and almost stalling till I reduce throttle. If I don't reduce, it will stall.

All I care about is the noise, and making sure I didn't make a mistake myself in setup.

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