High RPM dyno diagnostics?

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High RPM dyno diagnostics?

Postby Basil » Tue Jan 03, 2012 6:25 pm

I work with a lot of race engines, how would scopes in general, and the Picoscope in particular cope with a scenario I came across today please?

V8 race engine on an engine dyno with unidentified miss under load circa 8500 to 9000 RPM. Could be injection or ignition. 99% sure the engine is mechanically perfect. Engine is sequential injection, triggered by optical chopper disc crank sensor and optical chopper disc cam sensor. Ignition is capacitive discharge Lucas spark box, which is one CD driven coil feeding a mechanical distributor with rotor arm and cap sending the spark to the correct cylinder via conventional plug leads. A quick maths exercise in my head told me that at 9000 RPM there are 75 ignition and injection events per second, per cylinder, and if you looked at ignition pulses from the coil itself, or injector pulses down the common positive injector feed wire, 8 times this, or 600 events per second. I think that's right, anyway ;) Would a scope show accurate traces at this speed that could be useful for diagnosis? In today's example we found the spark box was faulty by means of substitution (it's usually a safe bet that if it's Lucas it's probably either gone wrong, or about to go wrong.... :)) Thanks.
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Re: High RPM dyno diagnostics?

Postby Wally » Wed Jan 04, 2012 4:54 pm

Have a look at this link and you will see two examples of canbus signals. On the first one, if you look across the bottom of the screenshot it is showing in "ms" per division and the second screenshot is showing "us" per division. I don't think you will see any missed parts of the waveform even at that speed.

https://www.picoauto.com/waveforms/CANBus/

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Re: High RPM dyno diagnostics?

Postby Basil » Wed Jan 04, 2012 5:01 pm

Thanks for that wally. Does the 4423 have the ability to stream data to the PC once the buffer is full, I call it a roll mode function, but people seem to have different terms for it? If so, given the above sort of scenario, once the buffer is filled what happens then? Is the data that is streamed acquired fast enough to replay later and see say a transient ignition miss, or stuck injector pintle that only occurs say once every 10 seconds or so?
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