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Automotive Diagnostics with a Cheap Handheld Oscilloscope

bobxyz said:
I think I'm now done proofreading and updating the main posts. I tried using the high-voltage ignition probe on the spark plug wires to capture the secondary coil waveforms, but this was beyond the capabilities of the cheap scope.

If you buy one of these scopes and use it for diagnosis, please post some feedback on the main instructions. If anything isn't clear, or needs more details, I'll see what I can do.

Next for me is to try a slightly better scope for ignition/injector/CANbus waveforms. I'll add another post below when done.
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I've purchased this setup and will be messing around with it! Thank you!
 
James M said:
On a related note the pico 2204a is a quite good entry level scope imo, I had good luck getting injector and canbus waveforms with it, although secondary ignition left a lot to be desired.
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I discovered the scope car diagnostics a few years ago and I had immediately falled in love with it.
Bob had reported only some of the main tests that can be made also with a cheap handheld scope that can save a lot of time in finding the causes of failures but the powerful of a scope is that can substitute near any other diagnostic equipment.
The pico 2204A is offered also without the probes and in my opinion is the best choice for who want a good scope for car diagnostics without spending too much money since most of the probes must be self constructed or purchased separately (eg. capacitive high voltage probes, BNC with cocodrile or banana jacks etc)
Also if the 2204A is the entry level model it uses the same very very powerful software that makes Picoscope so famous.
Just to list some very easy tests that can be made with a 2204A:
- check and tune ignition timing in real time
- find cylinder misfires thanks to a math function of the rpm signal (the same function used by modern ECU to find misfires on single cylinders)
- relative compression test (a very fast test than show if there is an unbalanced cylinder compression just monitoring the voltage drop at the battery during cranking)

But the list can continue for a long time and with the right probes many other advanced tests can be easily done (in cylinder pressure waveform analysis, intake pressure pulse waveform analysis, fuel pump state of health check and so on)
 
Truebeliever said:
Would this be able to test sensors off the car? I guess specifically a dsm cas?
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Sure, but you'll need to wire power, ground, and pullup resistors to the CAS. You could leave the harness connected but remove the CAS and spin it by hand. What issue are you chasing?
 
What sort of electrical noise is normal, say at the power supply pin to the fuel ECU (pin 9) or the ignition switch enable (pin 35)?

I think I can see the ringing of both the injectors and the ignition coil firing at these power pins. I am seeing like ~2v peak to peak at pin 9 which I think is coming from the 960/wasted spark ignition coil/power stage. Wondering if that is normal or if the stock power stage has some sort of clamping/damping circuit in it the 960 one doesn't. (I think this because it has a dedicated power supply pin that the 3 channel PS does not. But, just a guess.)
 
Measuring electrical noise accurately and repeatably is difficult, even with fancy equipment and lots of experience. The DSO152 is not at all useful for noise measurements due to its really low 200kHz bandwidth. On the other hand, the 200kHz bandwidth does filter out most noise so it's easier to see just the main signal, and you can connect the ground wire most anywhere.

The single-coil powerstage include a small circuit to buffer the 5volt spark input. This is all the +12v pin is used for. The 3 and 4 coil powerstages contain only the power transistors that ground the coil pin to energize the coil, and need a ~20mA 5v input.

What scope are you using? What's the bandwidth set to (if it can be set)? And how far away from the probe tip is the ground wire connected?
 
bobxyz said:
Sure, but you'll need to wire power, ground, and pullup resistors to the CAS. You could leave the harness connected but remove the CAS and spin it by hand. What issue are you chasing?
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Nothing yet, at somepoint I’ll be converting to cas and just wanted to check that it worked
 
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