Cranking-Tailpipe Pulses, annotated (After Valve-Clearance Adjustment)
Here is an annotated capture describing how all the "squiggly-lines" get on the scope screen. The vehicle's being cranked-over (at a steady cadence) and the waveform is zoomed to one complete engine-cycle.(720deg). The YELLOW trace is a tailpipe waveform from an inh20 absolute pressure transducer. Voltage increases positively with pressure. Although not visible, the waveform is synchronized by the #4 ignition coil command. The purple cursors are spanned across to each ignition event. This a 6-cylinder engine with one tailpipe. The firing-order is 1-4-2-5-3-6. The piston chart should guide you. Understanding how/why this tailpipe trace occurs aids in locating issue with :
LIFTERS CAM LOBES BENT PUSH RODS VALVE CLEARNCE VARIATIONS
All without disassembly!
...can it now be understood that if one of these valve opening/closing events were early or delayed (relative to their occurance between the purple-cursors), it would be visible here?
Thanks, I was worried how it would be received. My good-buddy recommended I do six separate annotations. That may have worked better but my concern was confusion from flipping between captures. Does the layout/color-coding make sense or can I better annotate this to make it more understandable?
It is kinda hard to follow on the left side but, it is the first time I've seen one annotated. Hard to digest. so much information in one capture. thanks for sharing.
I get it...let me know if you have any questions
Can’t wait to study this later.. really trying to get into pulse sensor stuff but it’s a bit more confusing than I thought initially
It just seems that way. Don’t make it anymore difficult than it is...simply pressure-changes over a period of time
how about instead of the lines across the screen just put the list of valve events right under the cylinder that it applies to similar to how the piston chart is above ? You could shorten Exhaust Push (Exh Psh) so it will fit. Since you color coded the valves to coincide with the the piston events it helps even more.
I do appreciate the idea however, multiple events from different valves/different cylinders occur in a very similar location. I’m not quite sure how to make it work the way you desire. Also, I’m not quite sure what you mean by “shorten the exhaust push”… I did not draw this, it was acquired from sampling from a tail pipe. Can you elaborate further?
The image in my head of what I want to relay doesn’t translate well so I understand. I’ll try to illustrate what I mean and get back to you. Thanks!
Sounds good, Im curious whatcha got 👍
It’s a crude drawing but this is what I see from your original chart that helps me understand the valve positions in relation to the cylinder positions with regard to the pulse waveform. Hope this sheds some light. And by “shorten the Exhaust push“ I meant to abbreviate the actual word not the actual waveform. (Which btw I knew you didn’t draw)😉
I see what you mean...however, because the transfer points are not identified in this drawing, it leaves the viewer still pondering how the squiggly-lines got on the screen. dont get me wrong, I know the chart i annotated is very “busy” and complicated. I find when I discuss this subject, most are confused heavily by the tailpipe waveforms, for the same reasons I annotated the chart in that…
Sorry I took longer than I wanted to respond to you. I think I agree with Nathan in that the first time I saw this I had to take a few minutes to sort it all out. Your annotations are clearly labeled for the 720 degree cycle. Your method makes sense. It makes it clear as to where all the valve events take place for each cylinder event. The IVO takes place in the same place in every cylinder…
Exactly!… So, I could leave annotations for one partition and leave the rest blank but with the color-coded dots remaining, correct?
Tell ya what...how about you “snip-it” and drop it into MSPaint. Erase the annotations as you see fit and repost 👍
I was actually going to attempt that before I initially responded. I was considering asking for the original waveform and permission to do so first. I didn’t want my attempt at redrawing to confuse anyone else following the thread.
Go for it!👍 ...I will have to get you the original waveform tomorrow. Dis you download the EScopeELITE or PRO software? (It’s free from ATS): drive.google.com/open?id=1H7b-j…
Thank you Brandon, Having the overlay above and the reference points on the wave form makes it easier to visualize. I am working to learn more and this is great. I have been messing around with home made exh pulse sensor. Looking forward to Super Saturday.
2 sensors for dual exhaust? How would you approach it differently? The typical pinhole exhaust leaks come into play here ? Or is there simply enough volume to still trust the diagnosis ?
Keith, all great questions! I have virtually ZERO experience with true SEPARATE EXHAUST streams. However, this will be carried out through study in the near future. I would have to approach it bank per bank/individually. minor exhausts leaks have almost no effect on the test result (common-leaks). It’s likely larger leak at a single exhaust runner may result differently. thanks for the…
Are the purple cursors part of the ats scope software?
Hi Dan, you are correct...but those cursors are available in overlay programs that can be purchased and is offered free with Windows10 (if I’m not mistaken)
Hey Brandon, Awesome post. I am trying to become more comfortable with using pressure transducers. Both in cylinder and out. As a total nube I try to first look for the anomalies in the capture and then determine how they relate to the issue(s) that I am trying to find. So, it appears to me that the voltage/pressure is higher before the 1,2 and 3 intake valves open. (TDC?) And it also…
Todd, thanks for playing... keeping in mind that the pressure transducer is measuring inches of water, the variations between pulses (in this known-good capture) are very minute. what can be seen is the proximity of the transitional points as they relate to the vertical purple-cursors. They are all very similar. If the valves in a particular cylinder were “misadjusted”, this would be seen in…
Brandon, I really like the annotations, this is helping me to understand this even more. I do have one question though. Is tailpipe more beneficial than intake? Or just easier or quicker to grab a capture?
Mike, i feel its easier to analyze intake as there is typically less activity. I use tailpipe pulses to corroborate theories I have based upon what I see in the intake Traces
I see that the peak of the exhaust pulse(TDC?) happens well before the ignition marker. Considering that the ign is advanced makes the exhaust pulse all the more advanced. If the exhaust pulse were slow getting down the pipe, it would be on the right side of the ign marker. The waveforms from the pizo type sensors, running, show the exhaust pulse peak to occur in time the ign marker. I’m…
Hi Stephen, the piston charts are just that. They don’t pay mind to valve action. It’s up to us to understand where these events occur. A six cylinder configuration has a combustion event occurring. Every 120 degrees. This clearly marked on the piston chart by the black vertical lines. The change in color is what represents the change in piston stroke. That MUST be every 180 degrees because of…
The main point that I wanted clarified is; why is the peak of the exhaust pulse occurring about 30* before the ignition event of the companion cylinder? Why is the exhaust pulse decaying before the piston reaches TDC? I knew what the divisions and colors on the piston chart represented. However your markup of the exhaust capture shows the valve opening and closing events in line with the 180…
Thank you Brandon! I found my new screensaver! I would love to see you do an annotated version of the intake pulses also. I’ve been attending classes on pressure transducers for a few years and have seen many hours of videos documenting the process and I’m slowly building my tool inventory to start practicing and capturing some “squiggly lines“ for myself soon! The first time I saw a pressure…
I’d be happy to do so. The intake traces are far easier to decipher.
thank you Brandon. Learning every day thanks for taking the time to educate us.
Thanks Joel, I’d like to help where I can. I know this subject can be diff to grasp. Getting over this “hump” will makes it far easier
Hello Brandon, I am currently studying your diagram and the explanation. I have been really eager to learn and decipher tail pipe waveforms. Since I am learning and have a few questions that I am trying to answer myself, is it possible to show an image of the pattern with the ignition sync ? I have been told there is a delay from the point of spark delivery and the exhaust pulse. Obviously the…
Hi Joe, although not visible here (because I turned the ignition trace ”OFF” for clarity), the first and last PURPLE cursor line up directly with the ignition strike. That should give you what you’re looking for
Likely due to a very minor difference in valve clearance... very similar to how we can have variations of compression from cyl to cyl. Keep in mind, this sensor is displaying inches of water...very subtle differece
So I’m trying to get some good waveforms and continuing learning this type of diag. with A running exhaust waveform there are actually 2 smaller humps after the large exhaust push. Is this explainable ?
Thanks Joe, would you mind “screen-shotting” the pic and encirclin the point you are referring to? This will help me to explain.
Its a 2015 honda crv 2.4 heres the waveform
Joe, please send me the SSC file and I will annotated/Re-post. Also, please describe what each trace is sampling from . My suggestion is to only use running —exhaust waveforms to find misfires. There’s far too much activity in the exhaust stream. Cranking waveforms will serve you much better
Stand-by, I’ll have a look...
Hey Brandon just wanted to follow up with you to see if you’ve had a chance to look at the waveform
joe, my sincere apologies as I was under the impression I had already responded (perhaps I viewed the waveform and didn’t respond). what the capture displays is four relatively-equal Pulses from all four cylinders contribution to the exhaust stream . The visible characteristic of the waveform can vary due to configuration and how many cylinder (frequency) of the pulses. the take-away is that…
Here is your waveform partitioned four ways:
its my pleasure, Sean. I truly hope you can make sense of my annotations
I didn't at first but after noticing you said it was synced to number 4 and knowing how the engine works, and knowing you probably used markers for the degree marks I got it
Hello Brandon! I know this is a bit older post/ discussion, have been studying it awhile ........ I have been trying to do some of this for some time . It seems that the exhaust airstream is quite noisy most of the time...... I use the firs look sensor also have the pico wps tool...... It looks like you may be using the tool from ATS that is used with the E misfire software, is this…