Pico scopes and such

[walterk]

I have recently started to delve deeper into problem solving with a Pico scope. in automotive applications, they already have a wide use and many libraries with waveforms, applications, etc.
I am wandering if any of you guys use scopes on Cummins engines? Where can one find "known good" waveforms? And, what waveforms do you find most helpful? I understand that Calterm is a very powerful meta data analysis tool, but surly there is room for a scope waveform analysis when solving issues form many different angles.

[MommaBurt]

they are more durable than your standard bench scope but i don't think they are better. I used them for troubleshooting can bus signals, injector signals, cam/crank sensor/ wheel speed sensors etc. it works well for that and if you roughly know what you should expect so you don't necessarily need "known good" signals. For example, one time I was looking at a cam signal on a cm870 and I saw the signal was like a shark fin and not a square wave. All I had to know was that it was suppose to be square and not a fin. We tore the front cover off and found the issue. In similar cases, I used it to troubleshoot all sorts of signals. You can learn what an ideal signal is from a little research.

[walterk]

Here I go again at it....
In the automotive gas engine applications, there is a substantial amount of analysis available on waveforms generated by a secondary coil testing, cylinder pressure testing, and injector testing. I am curious if that somehow could be replicated on diesels for in cylinder pressure/stroke/valve timing analysis? The access to injectors is not that easy and obviously no plugs and coils. Are you guys having good results with relative compression tests? If so, where do you find "known good" waveforms for Cummins engines or a diesel waveform problem analysis and case studies? The obvious problems are easy, but the nuances in performance are more difficult to pinpoint without a good waveform for a reference.

[Rawze]

Personally, I have never had to resort to extreme digital testing like that.

(injector leakage)...
Do an injector leak-down test on it...
ref: http://rawze.com/forums/showthread.php?t...2#pid69262

(compression loss)...

Running the engine on one or 2 cylinders at a time and comparing the differences.

Piston Rings can be tested for excessive blo-by while engine is idling by putting edge of a piece of paper over the oil fill with its cap removed. If there is then it don't matter what cylinder it was, as the whole engine has to be rebuilt any ways. A boroscope will tell you what cylinder(s) it is before disassembly.

- Valve adjustment vs. detent clearances, stem height per cylinder, will tell someone how worn out the valve seats are. Boroscope will reveal the rest if there is any suspects...

ref: http://rawze.com/forums/showthread.php?t...8#pid18718


... and worst case ... The cylinder head itself also can be tested by removing all the valve rockers and then pressurizing it (intake side, and then exhaust side) to 30 psi with all the valves closed ... and see if it leaks down.

[walterk]

Thanks Rawze, as always you are an Oracle of great of ideas. For me, the most intriguing thing about scope testing is how much you can find out about an engine performance and problems without getting your wrenches out. i just started to learn about these things, and I know these are big and deep waters..... Nevertheless, I will stay the course and try to learn and share that information with other members for our mutual benefit. Needless to say, i am hoping that some of our master diagnosticians here can chip in and shed some more light on this topic.