Erratic waveform/Noise in waveform

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Freddy LEE
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Posts: 3
Joined: Mon Nov 09, 2020 9:15 am

Erratic waveform/Noise in waveform

Post by Freddy LEE »

Hi, I hope everyone is safe and well in this uncertain times.
I need someone to tell me whether this erratic signal is due to my scope or coming from vehicle as I'm not sure why the noise is there sometimes when cranking.
The vehicle(2008 Honda Accord K24Z engine) which I have at the moment has a hard starting issue(cranking but won't fire) intermittently and DTC P0339 CKP Intermittent signal disruption coming on at the time of event but I can not replicate the issue at this stage. However I can see very low CKP noise count(about 2~3) and excessive CMP-B noise count(about 30) when looking at current data.
I did compare the CKP, CMP-A, CMP-B signals to known good signals and noticed that the CMP-B is half tooth different but I don't think the half tooth difference is causing the issue.
I suspect intermittent incorrect mechanical variable valve timing may be causing the issue but not sure as the issue is not obvious at this stage and I can't tell why there is noise in all three signals when cranking as attached signals.
Repair history: A new CKP sensor fitted
Thank you in advance. Freddy from Australia
Attachments
P0339 CKP & CMPs 1.psdata
(9.14 MiB) Downloaded 44 times

Steve Smith
Pico Staff Member
Pico Staff Member
Posts: 1097
Joined: Sun Aug 25, 2013 7:22 am

Re: Erratic waveform/Noise in waveform

Post by Steve Smith »

Hello Freddie and thank you for the post and the file

From the outset, I can see the disruption to all 3 signals starting predominantly on buffer 3

Buffer 1 we have noise from cranking which is quite normal given the electrical field dissipated via the starter and cabling

Buffer 2 looks “typical” and then buffer 3 we go from “typical” to considerable noise which is accompanied by an increase in engine speed

One possible cause could be our alternator now “online” and so charging commences

With that said, it certainly has an influence on our captured data which we can combat with filtering
More information on filtering can be found here post95821.html#p95821 and here https://www.picoauto.com/library/training/filtering

Using the filtering feature, we can see the true waveform that lies beneath the noise (See image below) and here you can look for any disruption relevant to P0339 detection condition
Image 1
Image 1
The PCM will most certainly remove this noise as part of "signal processing" and you can get a clearer indication of what the PCM can see if you measure with reference to the sensor ground (Given you have a 4425 scope)

It would be useful to check your test lead ground points (if measured referenced to chassis ground) and the routing of test leads across the engine bay.

Measuring the sensor signal at the PCM (not the sensor) may be helpful too (if this is not the case here)

If we prove the source of our noise is the alternator, then we could take this off line and note if the PCM continues to flag P0339

I hope this helps, take care…..Steve

Freddy LEE
Newbie
Posts: 3
Joined: Mon Nov 09, 2020 9:15 am

Re: Erratic waveform/Noise in waveform

Post by Freddy LEE »

Hi Steve, Thank you for sharing your knowledge.

I did capture the waveform again with the additional ground wire installed at the scope and I probed all sensor signals at the PCM connector and also all test lead grounds were connected to battery negative terminal.

Waveform 5 has about 2.5 Sec' cranking time(but no DTC) and the waveform 6 has the fault as the PCM triggered the P0339.

All signal waveform still has the noise and I can see the same noise at the ALT Battery wire as CH4 measured the ALT AC volt.

Note: I couldn't see the AC coupling function at the Pico scope menu but my snap on scan tool scope has the menu as I'm normally using the snap on scan tool to check ALT ac output. Can you tell me how to use the pico scope to measure the ALT AC output?

Unfortunately, the vehicle came to our workshop(Honda Dealership) just for the diagnosis from a local workshop and left without repairing the issue.

I wished to fix the issue but I may need to contact the workshop how they went.

Thank again and May God bless you..
Attachments
P0339 CKP & CMPs 6 NG.psdata
(5.67 MiB) Downloaded 39 times
P0339 CKP & CMPs 5 NG.psdata
(2.57 MiB) Downloaded 30 times

Steve Smith
Pico Staff Member
Pico Staff Member
Posts: 1097
Joined: Sun Aug 25, 2013 7:22 am

Re: Erratic waveform/Noise in waveform

Post by Steve Smith »

Hi Freddie and thank you for the feedback

These new files do not exhibit the noise level previously captured and the noise that remains is minimal. (This may well improve further still measured to signal ground)

Capture 6 has it all and I am suspicious of the charging circuit being responsible for the noise (I am not concerned about the charging system or the noise at this stage)

You will often see charging delayed post cranking/engine start as we saw in your previous captures
This depends on the charging strategy and a number of other parameters like prolonged cranking etc.

In Capture 6 I believe we can see momentary charging between the time rulers (high charge rate for approx. 500 ms) to recover the battery, followed by no or minimal charging until demand requires
Image 1
Image 1
You mentioned the DTC was triggered in Capture 6 but not in capture 5 (Forgive any misinterpretation)

Could you confirm the prolonged craning of capture 6 was deliberate or a symptom?
Capture 5 cranking time approx. 2 s
Capture 6 cranking time approx. 3.4 s

Both captures have the noise post cranking and both demonstrate “floating” crank and cam signals during the cranking phase (drift from zero-volt ground reference)

Whilst the floating may be normal, can we check ECU and chassis ground to battery negative volt drop?

Could we research the detection condition for P0399, i.e., what are the exact conditions that have to be met before the ECU will flag this code?

I have looked at correlation at idle and compared to a donor from our Waveform Library thanks to “ghenke” (below is a K24V engine)
Image 3
Image 3
Below is your Capture 6 shortly after start up (Note AC Coupling can be found by clicking on your channel options button)
Image 2
Image 2
From the above data, Cam Crank correlation does not appear to be an issue after start up.

I hope this helps in the interim, take care…..Steve

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