I've been working on verifying the cause of an intermittent misfire on a 2003 Nissan Sentra with 1.8L QG18DE inline 4 cylinder engine (petrol). It has about 90k miles on it, and seems to run OK at idle, however I have noticed an occasional misfire when driving the vehicle on the road. I have a Pico 4425 and the TA204 handheld COP probe with TA033 BNC cable. The software version that was used is 126.96.36.19938, and the BNC ground clamp for the probe was connected to battery negative directly. The probe was held flatly and solidly against the smooth top of the COP unit for all traces. This vehicle is equipped with the OEM Nissan COP units.
I keep getting what appears to be an upside-down waveform using the handheld COP probe, regardless of the cylinder involved. Looking at the factory-supplied probe configs, I don't see one set up for the handheld COP probe with an inverted waveform that would flip this for me. I am wondering if this Nissan Sentra is using a negatively fired ignition system, or I am just doing something wrong.
I really want flip this waveform so that I can visually confirm what I am seeing in the measurement maximum/minimum statistics, which are firing voltages of between -40 and -80 kV. I cannot see this on my scope waveform, it appears to me as if the waveform is cut off in the negative voltage region. This makes sense to me since the ranges available for the COP probe do not appear to encompass such high negative voltage values. I want to visually verify in the waveform the existence of the high voltages that the measurement statistics appear to be indicating, before I attempt any snap-throttle tests etc. and start trying to address why the firing voltages are hitting such high negative peaks and what might be causing it.
I searched the forum but cannot determine whether this has already been seen for the TA204 COP probe.
Since I don't see a factory-supplied inverted probe config for the handheld COP probe, what are my best options regarding how to custom configure the scope so that I can see the entire secondary waveform for this vehicle? I'm willing to create a custom configuration myself to address this if necessary (with software prior to 188.8.131.5238), especially if someone gives me some basic guidance on setting up the ranges and advanced parameters recommended for the COP probe. I read the user manual last night and some of the parameters I believe I would need to invert the trace appear to be intended for "factory use only", but this is just a guess. I am open to any good suggestions regarding how to view this waveform, or what I may be doing wrong.
I have attached four PDF files of waveforms with measurement statistics for all cylinders so you can see what I am referring to.
Thanks in advance for any and all help!
UPDATE 12/30/18 1:27pm EST: Thanks to forum member Speck's suggestion, I now know how to use math channels to invert the waveform (see responses below) and other cool functions. However, this does not give me any more visibility into the negative voltage range, so what I have now is an inverted waveform where the spikes I am interested in are still cut off at 5kv. I'm currently investigating how I might create a custom configuration for the handheld COP probe with an expanded negative voltage range so I can see these spikes. Of that means running the tests all over, but it is what it is. Appreciate any helpful comments!
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How about using Math Channels and invert the channel you want.
Would adjusting the scope settings using the lower tool bar as shown here help any!
Thank you for this excellent suggestion, I had not used the math channels function before as I have not completely read the entire 224 page user guide. So I worked with it this morning and it does indeed invert the waveform for me. But unfortunately it does not give me any more visibility into the negative voltage range (i.e., I don't see anything beyond -5kV displayed in the newly inverted waveform).
So I guess what I really need to figure out is how to re-configure the ranges for the TA204 handheld COP probe so that I can see up to -100kV. Preferably a range of +100kV to -100kV would be perfect, but I'm not sure if that possible. Having both an inverted trace AND an expanded negative kV range would be exactly what I need to see the entire waveform in this case.
Really appreciate you making me aware of the inversion capability with math channels. I am definitely going to read ALL about what I can do with math channels, seems like an extremely powerful capability, thanks again!
Thanks Technician, I appreciate the reply. Yes, I thought that might be helpful early on, but I read on that those icons refer to setting whether the trigger set pertains to a rising or declining voltage level. That was actually helpful to me when I configuring my triggers initially, but I'm afraid won't help me much with inverting the waveform or expanding the negative voltage range. Perhaps I need to investigate how I can somehow create a custom probe configuration for the COP probe that will give me more visibility into the negative voltage range. Unless there is a better idea, of course!
This way you can use it live. You have to install older Pico version though because latest is faulty and crashes on probe editing.
Thanks very much volrem for the suggestion. That is exactly what I was thinking as well, and your confirmation that I am on the right track is greatly appreciated! I am going to work on that today.
I ran into the issue you describe with the latest software release, but Martyn and Tom Roberts have indicated where to find previous versions that are not affected by the probe configuration bug in another post.
It's all a big learning curve for me as wellStiletto wrote: ↑Sun Dec 30, 2018 6:15 pmThanks Technician, I appreciate the reply. Yes, I thought that might be helpful early on, but I read on that those icons refer to setting whether the trigger set pertains to a rising or declining voltage level. That was actually helpful to me when I configuring my triggers initially, but I'm afraid won't help me much with inverting the waveform or expanding the negative voltage range. Perhaps I need to investigate how I can somehow create a custom probe configuration for the COP probe that will give me more visibility into the negative voltage range. Unless there is a better idea, of course!
I also wanted to have an inverted COP probe config so I duplicated my newly created COP probe config and tried to edit the custom ranges and add "Invert Always" in the Edit Range > Advanced configuration panel to each of them. Interestingly, I found the Pico software would not allow me to simply add inversion to an already existing manual range. I had to delete all the ranges that were copied and define new ones altogether with inversion specified. Not sure if that is by design, user error on my part, or an anomaly in the software. But the end result now is a COP probe config that has "Always Invert" specified for each range.
Will run this against the vehicle later today and see if I am able to see the full range of positive and negative voltage spikes, as well as if my inverted probe configuration works. Hopefully this yields the desired results.
- The expanded range I created worked perfectly, I can see the full extent of the negative firing voltages in the waveform;
- Using a custom probe configuration to produce an inverted waveform without the use of math channels using the Edit Range>Advanced "Always Invert" configuration option failed. I also tried the "Invert When Negative" option, same results: the waveform produced was appeared identical to that produced with "Do Not Invert".
OK, so that being the case, the good news is that combining the use of my new ±100kV range with the inversion capability in math channels gives me a viable workaround for now. However, if I am not using the inversion options correctly in the probe configuration, I'd appreciate knowing that, please chime in and let me know how to use it correctly.