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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
 
I bought a DS0-152 for $30. I am playing around with it. I was trying to graph the 02 sensor waveform today, but all I could get it to do was a flat line that was going up and down. I copied the settings from post 4.
 
ZVOLV said:
I bought a DS0-152 for $30. I am playing around with it. I was trying to graph the 02 sensor waveform today, but all I could get it to do was a flat line that was going up and down. I copied the settings from post 4.
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Are you able to adjust the scaling? If you are getting a long line with a little up and down it sounds like it's too "zoomed in" on the length of time and too "zoomed out" on the voltage. A standard O2 sensor voltage scale should be around 1 volt.
 
I bought the 1014D big white box version (7”diag display) with knobs to play with, because kids learning need to see me making changes along with the graph changes.
It is 100mhz, but that is enough for teaching. It has usb power, so i use a power bank for testing in the field. It’s pretty good. Used it to rule out an AMM and shoot down a crank sensor.
I am ordering 5 DSO-510 handhelds and a tablet with 7” display.
*edit: those are all school purchases made with funds from repairs. Money is getting tight. I need to crank up the income and get the program right for the next guy/girl. I’ll buy one for myself when i retire.
 
WagoneerIntakeCamvsRamIntakeCam.jpgRamIntakeAndExhaustCamsVSCrankshaft.jpg


I am working on a truck that has a cam/crank correlation DTC. The top screenshot is from a known good engine with no DTC. The bottom screenshot is from a vehicle with a cam/crank correlation DTC.

Blue=Crankshaft sensor
Red=Intake cam sensor
Green=Exhaust cam sensor


I think I see a problem, but I am still working on diagnosis. I would like to get a couple more "known good" waveforms before I make my conclusion, but what do you think is the problem based on these two screenshots!? (Clue: look at the green waveform relative to the gap in the crankshaft sensor waveform.)
 
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I've just picked up a DSO510 from eBay, which is very similar to the one which @bobxyz wrote about in the first post.

Figured I need this thing to sort out why the cruise control won't work in the 1998 S90, since the vacuum lines, etc are all okay and none of the local auto electricians seem to be able to fix it.
 
apollokid said:
It seems that the exhaust cam on trunk with DTC is advanced, what's happen of you rev up the engine?
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Yep. I believe the exhaust cam is off-time. It looks over-advanced at idle.

The crankshaft reluctor is a 60 minus 2. There are 58 teeth and 2 missing teeth. 360 degrees/60 teeth= 6 degrees each crank reluctor tooth. I see the exhaust cam is advanced about 4 crank reluctor wheel teeth, or about 24 degrees, relative to the to the "known good" exhaust camshaft timing waveform.. So that means the camshaft is physically advanced 12 camshaft degrees compared to the known good exhaust cam, right? I am guessing we may be off one tooth advanced. The tech just did timing chain work and ever since he messed with it, there has been a P0017 cam/crank correlation code. They swear they physically checked timing already, but we know the computer is probably right that there is a timing issue.

I didn't have a chance to do anything but idle readings. The cams should be zeroed at idle. Of course cam timing will change at higher engine speeds/loads. What would YOU be looking for?

I was trying to learn how to use the rulers in Pico 7, but I kept having problems keeping them where I wanted them due to zoom in/out issues.
 
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By eyeball, the good waves have the rising cam edge ~4 crank degrees into the missing tooth gap, and
the bad waves have the rising cam edge ~2 teeth, or 12 crank degrees before the gap,
so a difference of 12+4 = 16 crank degrees

Do you know how many teeth are on the cam cog? 16 crank degrees or 8 cam degrees is pretty small for being off a tooth. Maybe the phasor is hanging up?
 
bobxyz said:
Do you know how many teeth are on the cam cog? 16 crank degrees or 8 cam degrees is pretty small for being off a tooth. Maybe the phasor is hanging up?
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I do not know any type of tooth count. Whatever is on a 3.0L twin turbo straight 6 Hurricane engine.

There is a chance the person went in there without using the proper camshaft holding tools and mistimed the engine. The camshaft timing is going to be physically rechecked.
 
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