Introduction to Engine Cylinder Pressure Analysis and Diagnostics

How to use a pressure transducer to analyze engine problems that cannot be detected through traditional means such as leakdown or compression testing.
Visit my pay channel at www.schrodingersboxQM.com for more in depth training videos as well as to download my Engine Diagnostics book!!
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[@GAZIS4]

I have been taught in tech school back in 80s that valve overlap happens because we use the inertia of exhaust gasses in order to create vacuum achieving better scavenging of exhaust gasses due better intake and better stoichiometric efficiency in the cylinder.

[@mechanic_marky]

It's nice to see you posting more videos. I did sign up for your paid page as well. I've been a heavy diesel tech for 17 years and love the electrical side of the work. I have a 4 channel pico but caterpillar has such a great program it isnt really a go to tool for me yet. I really enjoy your method of analyzing and diagnosing vehicles. Thank you for your content.

[@SchrodingersBox]

Thanks for your support!! Man a 4 channel pico- I am officially jealous!!!

[@6siqueira]

I found your channel and really enjoyed it, I'm from Brazil and we don't have this kind of technical information level here by far. My english is not very good but your english is extremely clear, paused and easy to understand, you have no idea how much you are helping me to understand in a way no one here would be able to help, please keep up

[@SchrodingersBox]

Awesome, thank you! I do get that comment a lot from people who don’t speak English as first language. it’s a very good compliment and I am glad I am clear for you.

[@darrendesmarais8124]

Great video Matt. The best non-invasive way to check any issue inside the cylinder.

[@JohnDoe-sp8zg]

I haven't finished watching the video but I am impressed by your passion to teach and your delivery. The experts should take a chapter out of how to deliver their content. While one guy was giving helpful tips he might have missed the audience for this video. Intro and basic level understanding of transducers. No overwhelming us with expert level video for beginners class. Spot on

[@SchrodingersBox]

Oh wow thanks!!! I do enjoy it!!

[@glenntagaylo2339]

Awesome! I've been looking for this back pressure issue for a long time. Thank you for all the effort you have put into all the details of the video. Really helped me alot in understanding things like this. Thank you.

[@richarddiaz591]

Fantastic analysis! Thank you.

[@helgikristjansson4702]

Excellent video. Tanks again for the education.

[@SchrodingersBox]

Thanks for watching!!!

[@MarzNet256]

That's pretty cool. It would be interesting to actuate the VVT solenoid(s) during idle and see what happens to the waveform.

[@astrologando1858]

Looks like your new car needs adenosine, it's in SVT!! :)) Awesome as always!

[@SchrodingersBox]

Hahaha I always appreciate science and medical jokes!!!!!

[@waynedavis1214]

Explained very well and in detail .

[@abderrahimmark]

Thank you very much, Matt, for everything. 🙌🏻❤️🌹

[@SchrodingersBox]

Thank my friend!! Appreciate your support!

[@PaulCTownsend]

Explained really well thank you.

[@ThunderbirdRocket]

This is so good … definitely makes the short list among the best presentations on the subject anywhere ! At 47:25 I zoomed in to read the back of your t-shirt 😆and enjoyed a big laugh while agreeing profusely ! Thanks mate !! 🎯 👊🏼

[@SchrodingersBox]

HHahaha I didn’t even notice the shirt but yeah, glad we connect hahahaha.

[@TheDisgruntledMechanic]

thanks Matt. I need to get my pressure transducer out of the case more often! I've only used it probably 2 times. great video and explanation.

[@SchrodingersBox]

Man I use it almost every compression test now. Experimenting with intake waveforms now as it’s a great way to get data if the cylinder of interest is under the intake manifold which is the major limitation with in cylinder pressure testing.

[@TheDisgruntledMechanic]

@@SchrodingersBox yeah when I retire for the 2nd time I plan on doing more of that kind of stuff.

[@Pablo_Automotive]

Great video Matt

[@SchrodingersBox]

Thanks as always my friend !

[@vilhelmholmberg8825]

Thankyou! Very interesting. Keep em comming

[@SchrodingersBox]

Thanks, will do!

[@fredautos]

Thats explanation was interesting matt..

[@SchrodingersBox]

thanks!! i really think this is one of the most powerful techniques out there!!

[@fredautos]

@@SchrodingersBox yeah I'm a beginner on this. This video brought more light.ti me.

[@alkisgeorgoudis1981]

nice work well done

[@sheerwillsurvival2064]

Great video Matt 👊🏻👍🏻

[@SchrodingersBox]

Glad you enjoyed it!!

[@josephfaro9013]

Great video. I am looking forward to the "mystery truck" diagnosis.

[@SchrodingersBox]

Just posted in at www.schrodingersboxQM.com. It’s a good one!!!!! You tell me how it would be diagnosed without this technique!!!

[@Mr2004MCSS]

Very good video and explanation of how it all works. Ivan from Pine Hollow Auto Diagnostics sells a transducer set for about half the price of the Pico setup. He also has a nice playlist on his YT channel of his use of his pressure transducer in various diagnostic case studies. Jarhead Diagnostics also sells a VA sensor that can do some of the same things.

[@SchrodingersBox]

Thanks for the info!

[@Dr.AymanKamar]

Great video my friend

[@SchrodingersBox]

Thank you! I will be adding this to the next edition of the book for sure!!

[@canadatransistor]

I think there are also some pressure transducers that can be affixed at the exhaust tailpipe. This could be helpful identify bank to bank differentiation in dual exhaust and a number of conditions including misfire events. Of course, the exhaust can't be riddled in bullet holes etc. This allows for all cylinders to be firing and monitor for things like cylinder wall wear or piston rings not sealing correctly.

[@SchrodingersBox]

There are indeed. You can also modify a cone or something to make it work in just about any transducer. A delta transducer is usually more useful for these applications.

[@Car_Amoz]

excellent

[@tshephokgetjepe3162]

We are spoilt this month ❤, as non paid channel subscriber ......

[@SchrodingersBox]

Hahaha you should become a paid subscriber then and REALLY be spoiled!!! My best videos by far are on the paid channel.

[@martinarrieta248]

Grasias

[@aymenmohamed1134]

Awesome

[@DuaneDonaldson]

As for the scope setup, some scopes will not zoom in and some will not zoom out based on where you are when reinspecting the waveform, newer scopes are moving away from this problem. What we ask these days is Apples to Apples, if you capture a bad waveform and maybe additional waveforms, and then after repairs, you show the known good waveform, please use the same settings as the initial waveform and the same channel (color) on the same sensor so we do not need to do any math or think about mistakes in set up, to be able to give you some feedback, diagnostic direction, etc. It only takes a minute to pull up the old trace and set up the scope in the same exact manner to grab a new pattern, fixed or not fixed yet. When you take a screenshot to share to ask for help, post the entire scope face with all the settings visible so we can try to figure out some voltages and timing settings, we need to know what you know. This is a serious problem when folks use their camera to share pics, they get too close to the screen and don't show all the parameters in the margin. So you are not into drifting as they use all 3 pedals with only 2 feet LOL. If you lose compression for some reason, the TDC is not actually TDC so your 4 180* regions will not be exact measurements for cam lobe timing but that comes with more experience. I highly recommend that you keep a library of valve timing degrees, Different makers design in different valve timing and valve overlap in degrees. Some Mopar like to open the exhaust valve very early, 50 to 60* BBDC whereas most engines are around 30 to 45* BBDC. You may also get some VVT malfunctions and with a library of known normal timings, you will see ASAP what your malfunction will be and no need to keep it in your brain, why is this engine opening the exhaust valve at 55* but it's closing on time, hmmm. The downward slope after 360* should pass through a ruler set at 380* for a quick check, again your library will show you the engines that don't normally follow this rule of thumb, once you build up a nice library. You mentioned Atmosphere, this place on an Intake Vacuum will be seen in several places that you will mark on your waveform in PAINT as ATM. This will depend on the type of transducer that you are using and your waveform will waver a bit at ATM when moving from a pressure to a vacuum & visaversa, this is a telltale sign that you are traversing from one state to the other and this can be used as part of your DIAG and can come in handy. Is your car a turbo? On your running waveform, you have a small increase at the end of your exhaust stroke, this can show a slight restriction of the turbo, valve timing overlap can come into play and we need to be aware and keep this capture in our library as normal. If you start to use and teach the color-coded Piston Overlay, be aware of the CONS before you start teaching it, HINT, valve overlap and when the valve actually start to move, not at 180*, 360*, 540* as the colors would lead you to believe, it's only a guide, it sucks as an actual tool but its better than nothing. PROFESSIONAL TIP, do not count on getting a large collection of waveforms online, many techs consider their waveform collection as GOLD and do not share them for free out of the goodness of their heart. If you have a PICO Scope, you need an automotive level = more expensive model, or you cannot get into the PICO Library for free. You might find a nice FB Group of waveforms but if they see you downloading too many, they will BAN you from the Group. If you join a pay subscription site then this is a great place but some subscriptions are not cheap so you also need to add that cost to your labor knowing that your customers are the ones actually paying for subscriptions, not you. This is just one reason why shops are expensive vs the cheaper shops who don't pay for much on the side. AUTONERDZ is a great resource as I have known them for over 25 yearz, and I don't want to flood your comment section with many others to drive business away.

[@SchrodingersBox]

All good advice. Also good point about the scope zoom. I often by habit just set my picoscope for an almost unreadable zoom out knowing I can always zoom in on it. On my Vantage pro- I do the exact opposite. It’s best to zoom in to where the signal is unreadable and then zoom out to analyze it.

[@jordysandino6577]

Hello sir . Good video by the way. Quick question that wave form only represents per Cilinder right So if this is 1 is nomarmal Cilinder 8 could be bad right?

[@SchrodingersBox]

Correct. It’s only one cylinder. You either need a good waveform FOR THAT SPECIFIC CAR for comparison or a known good cylinder in the same car.

[@therealspixycat]

There is a linear relation of the voltage output and the measured pressure right? Plus you can do similar analysis on the voltage trace of an injector to see the actual injector opening and closing

[@SchrodingersBox]

Correct. It is linear.

[@carguy1312]

Hahahaha, love that shirt! Btw - pico 7 is just outstanding imho. Have you tried it? Can always revert if you hate it…

[@SchrodingersBox]

yes I love pico 7!!!!! i used it until i got a new laptop and came to find pico 7 is incompatible with the graphics card so i sadly had to revert back to Pico 6

[@anthonyharrell6078]

Have a question can this scope be used in the air conditioning world to check internal bypass of a automotive compressor issue we’re hi and low air mixing causing poor performance issues

[@SchrodingersBox]

YES!! I have absolutely read where AC technicians use scopes for exactly those purposes!!

[@bradensmith888]

Hey Matt, I'm having trouble diagnosing a coolant loss issue on a 2016 Honda Civic. The car has never overheated, but the (pressurized) expansion tank needs to be refilled affer every 7 hrs of driving. The only visible leak comes from the overflow tube on the expansion tank. I've pressure tested the system, and I couldn't find any leaks. I used a combustion gas analyzer fluid, and it did not indicate a blown head gasket (tested with engine cold and warm, couldn't get it really hot). Thinking that the only component remaining was the overflow cap, I replaced it, but I'm still having the same issue. Do you have any advice?

[@SchrodingersBox]

I would only trust a leakdown test to confirm it isn’t a cylinder head issue. That’s what I would do next. If that passes it’s possible you are losing cooling through and intake manifold leak. That won’t show on combustion fluid, compression or leakdown.

[@jason200792able]

I wonder if this could be done on the uscope?

[@SchrodingersBox]

Yes it can!!!

[@bekomcar554]

So, for 4 cylinder engine should I do all 4 cylinder testing or just any one cylinder for the engine performance?

[@SchrodingersBox]

It depends. This is a single cylinder test so you really have 3 strategies: 1. Isolate the bad cylinder through other means and use this as validation for why there is a failure 2. Test each cylinder until you find one with a blatant anomaly 3. Test all cylinders and compare with each other and look for the one that’s different.

[@asherman6473]

How do you like the Bronco?

[@SchrodingersBox]

Absolutely love it. Great ride, great power and it’s a stick shift- 7 speed!!!! I honestly didn’t know they still made stick shift anymore hahahaha. I thought they discontinued those in 2022

[@user-hr5dc4ly3q]

Hi master can you test same work but use picoscope with any car oil pressure sensor because it will cheap than $1000 picoscope pressure sensor

[@SchrodingersBox]

great question. while essentially the picoscope pressure sensor is no different than any MAP sensor or oil sensor or any other 3-wire pressure sensor, the trick is it has to be able to handle the very high pressures of cylinder compression. In some cases you will subject the pressure sensor to as much as 300+ PSI during pressure testing (such as snapping the throttle or torque-braking the engine). so just any sensor won’t do. it needs to be able to handle the high pressures in the cylinder.

[@fastestcaskets5020]

I use the refrigerant pressure sensor from a Nissan Altima with 5v and ground from the USB port on my scope. No real good voltage to pressure conversion, but very good waveforms.

[@SchrodingersBox]

Oh wow that’s a really good idea!! And it would handle the higher pressures too. Great idea!!!

[@DylanL69]

You can do a compression test with the engine running it's a called a running compression test and compression is lower when you do that test

[@SchrodingersBox]

How is that done and how would the gauge “lower” from a peak compression?

[@DylanL69]

@@SchrodingersBox you put a compression tester on 1 of the cylinders and fire the engine up. Compression is just naturally lower because the compression strokes happen faster.

[@SchrodingersBox]

Yes but look at the waveforms I got. Initially there was a peak compression that was essentially normal. But then when the lifter failed the compression was only 132. How are you going to see that 132 on a gauge after a peak compression already hit at 300???

[@DylanL69]

@@SchrodingersBox that idk I don't think it would show on the gauge

[@SchrodingersBox]

Exactly. A gauge catches the peak compression. You won’t see a variance with a lower compression that happens afterwards. IF the compression was steadily low then that would work. However on this case it would just capture the normal peak compression.

[@RobMonte]

What or how does a cars computer determine 2 trips?

[@SchrodingersBox]

Yeah that’s a great question and important to know since two-trips is generally needed to set the check engine light. It’s two cycles of the car being driven with conditions consisting of a certain amount of idle, a certain amount of low speed driving such as city driving, a certain amount of driving over 50mph with a constant accelerator position such as on a highway, and a certain amount of decelerations like going downhill. A service manual usually defines the time periods for each of these. If you ever took your car to an emissions place where they put it on a dyno, you will see them do two drive cycles like that on the dyno “trying” to cover all conditions where a check engine light might set.

[@RobMonte]

@@SchrodingersBox Thank you :)

[@alinduta5398]

be carefoul when testing diesel only cranking,no runing diesel because presure is to big and you can damage the transducer

[@edtornick3587]

Signed up and paid for the advanced channel. Cannot log in and no response to my many requests for support. Starting to think the paid subscription is a scam.

[@SchrodingersBox]

Your PayPal email and your website email don’t match. They have to match.

[@edtornick3587]

They do!!!

[@SchrodingersBox]

Ok send me an email to [e-mail]. I’ll fix it personally.

[@tshephokgetjepe3162]

We are spoilt this month ❤, as non paid channel subscriber ......