Spark/injector diagnosis with oscilloscope?

[Jazz_89]

This goes to the geeks out there^^ I recently got a dual-channel analog oscilloscope as well as a signal generator and I am planning to visualize the spark timing and the injection pulses together with crank shaft angle. The setup uses coaxial BNC cables.
Is it possible to measure these signals during closed loop operation, i.e. without intervening to the engine performance? Do I need to unplug the corresponding connectors and do the voltage measurement in parallel configuration? Is there a risk of damaging the ECU?

Any advise is welcomed

[whiskychaser]

There should be enough input impedance in your scope to prevent interfering with proper operation. The only way I see you damaging the ECU is if you short something out. You might find this of interest:
http://www.electro-tech-online.com/threads/using-oscilloscopes.212/

[Coyote_ar]

what kind of diagnosis you intent to perform on the injectors? i dont think you can get any information about the injector with the osciloscope. you will be able to see the signal that the injector is receiving from the ECU, but not what the injector is doing with that.

also, if you intent to watch spark/injector pulses, i would definitely pickup the signal from the crank position sensor (its a VR sensor if im not mistaken).

so you would be able to overlay the injector/spark signal, with the crank position which is the real "heartbeat" of the engine.

[Jazz_89]

Thanks for the tips: I will try to overlay the signals to the crank shaft position signal. Will return with an update probably

[Jazz_89]

Almost there. Does anybody know if a 1 MegaOhm oscilloscope probe is suitable for back-probing a crank position sensor or a fuel injector? Will the back-probing needles/cable reduce the measurement probe impedance further?

[632 Regal]

Wow... we haven't had questions like this in at least 10 years. I doubt any of the people capable of helping you frequent this forum now. I find it highly knowledgeable though.

[Coyote_ar]

i think thats fine, if i recall my physics classes ... when you were measuring resistance, the testing device had to have a HUGE resistance compared to what you were measuring.
so if a low impedance injector is about 1.5-3 ohms, and a high impedance is 10-16ohms. 1 mega ohm should do the trick.

[Jazz_89]

Ok thus makes sense. My devive has a input impedance of 1 ΜΩ, so I guess this is appropriate.