Paccar Injector analysis with Michael Eilbracht

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ben.martins
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Paccar Injector analysis with Michael Eilbracht

Post by ben.martins »

Hi all,

Nice video here from Michael over at MJE Diagnostics showing how the scope can help diagnosis injector issues when there are no codes.

https://youtu.be/ceHULlITDX4

Enjoy!

Kind regards

Ben

PaulW
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Re: Paccar Injector analysis with Michael Eilbracht

Post by PaulW »

What voltages have you seen Cummins injectors peak at?

ben.martins
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Re: Paccar Injector analysis with Michael Eilbracht

Post by ben.martins »

Hi Paul,

Injector voltage levels between engines can vary. From the injectors I've seen it sits somewhere between the 50V and 150V. This can either be the driving voltage or the fly-back voltage once the injector is switched off.

The new 4425A is more that capable of handling these voltages but for the older Pico's, or if you're ever just not sure, it's always best to use an attenuator.

Not sure if that helps or not!

Kind regards

Ben

PaulW
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Re: Paccar Injector analysis with Michael Eilbracht

Post by PaulW »

Hello Ben,
I was just curious what the vertical would be set too. Not on any particular scope just in general. You welcomed me in my introduction post and mentioned my pocketscope I had received last week. I now have a 2204a in the mail and on the way. Been playing with PicoScope 7 in demo mode to keep me patient. Thanks for the information.

ben.martins
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Re: Paccar Injector analysis with Michael Eilbracht

Post by ben.martins »

Hi Paul,

I would always go high, that way you can always come back down the range but you'll always see something.

If you have the 2204a on it's way and looking to scope injectors please make sure you use an attenuator and connect to one side of the injector and the reference to chassis. Attenuators only attenuate the signal side which means the ground, if floating across an injector, could be hit with a high fly back voltage which could damage the scope. Also consider that if you are using the other channel then the ground side will also see this voltage and depending on the connection could damage a component. Finally, the USB ground for the scope is also connected to the BNC ground which could result in this same fly back voltage getting into your laptop.

I don't want to put you off getting stuck in with Pico and measurements, far from it. Just encourage caution when connecting to signals where the voltages may not be known.

Look forward to hearing how you get on and your contributions to the forum!

Kind regards

Ben

PaulW
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Re: Paccar Injector analysis with Michael Eilbracht

Post by PaulW »

Hello Ben,
Thanks for the heads up. I had a 20:1 attenuator in line on an Cummins ISB 2350 and found the injector peaking around 55V. I had the negative of the scope lead going to battery negative as I have trust issues with the chassis grounds. I was getting intermittent spikes with Picoscope 7 T&M early access. I ordered new leads and I will take another waveform. The spikes would got over 80V with the attenuator but would also go into the negative range on. Not sure if the leads are the issue but will try singling out 1 by 1 to see if something I am doing is causing the spikes (and drops?). Thanks for any help. I appreciate any knowledge and input as I do not know it all by any means.

ben.martins
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Posts: 396
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Re: Paccar Injector analysis with Michael Eilbracht

Post by ben.martins »

Hi Paul,

It sounds like induced voltage into the test leads potentially. It might be something on the ground side back feeding but hard to say. If you get a bit more time on the capture, say 50ms/div you should be able to tie in any interference you're seeing with another timed event. If you aren't using shielded leads then this would definitely help reduce the spikes.

If in doubt then current clamps can help reduce the risk of an over voltage. If working with solenoids it is sometimes the preferred option as it shows you the work being done.

Happy scoping and let us know how you get on.

Kind regards

Ben

PaulW
Newbie
Posts: 9
Joined: Tue Jul 26, 2022 5:37 pm

Re: Paccar Injector analysis with Michael Eilbracht

Post by PaulW »

Hi Ben,
Again thank you for the input and possible issues. Thinking back to when I was scoping, I was not using shielded leads. I have new leads on the way. I'm going to begin with lower voltage ckts first. I didn't even think about induced voltage as causing an issue but will think about this in future scopings. I will try injectors at a later time.

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