Relative compression test without an amp clamp

Any two channel scope will work for the test I’m going to show in my video. All scopes work by plotting voltage over time. There isn’t anything special about the Pico in this regard. Although in my opinion, the Pico far exceeds all other scopes in so many more ways, it isn’t any better than any other for this test.

Relative compression testing is measuring the effort a starter motor uses to compress each cylinder and comparing the results across all cylinders. It is a very quick test. It is a go, no go test that I recommend before any parts are replaced for any running problem on a car.

Using the amp clamp you are using a tool that outputs a voltage for the scope to read based on the amperage going through a cable. Using ohms law, we know that amps and volts have a direct relationship with each other. So what we are going to do is measure the voltage instead of the amperage and get the same results.

I will prove this in the video by showing both voltage and amp clamp measurements side by side.

A couple of things I failed to mention in the video. First I already disabled fuel. I did that by unplugging the fuel pump under the back seat on this one. You have to disable the fuel so the engine will crank without starting. Second is I’m sorry you have to listen to my voice. I don’t like it anymore than you do.

[NewLevelAuto]

Really glad you decided to share this .

[paulabend]

Nice video. If you invert the voltage waveform it will look just like amp clamp waveform

[Autofixpals]

Very Nice! I was thinking that you could probably do RC using DC volts as well but i never tried it myself. I Have seen it done using AC as well. Thanks for sharing.

[dtnel]

Good video! Just wondering why the title says "without amp clamp" when one was being used? Did I miss something here?

[andyamanda]

So basically you don't need to use a clamp meter ! just measure battery voltage and inverse image ! Thanks for sharing .... Quick question - was the voltage taken at the starter motor or the battery terminal please ? Thanks

[sandyande]

Thanks for sharing this, great looking video what camera are you using? Cheers sandy

[vitok]

how is it without an amp clamp??? and yeat i see one connected.