Compression tests - Conventional vs. Labscope 

No, thank you for taking the time to teach us. As someone else mentioned, I thought a RC test could only be performed with an amp clamp. Have an awesome year!

Hi Brandon I am motor nechanic for over 50 odd years (15 years in Europe, rest here in Adelaide, South Australia. Still have opportunity to learn a lot. Thanks for posting it. Time watching new techniques is time well spend. George - QQMR

I appreciate you taking the time to watch and for your feedback

Thought that was you in the background.

He's a rockstar indeed. I would recommend yall to attend a class of his live! One of the best in the industry in my opinion - Brian Culotta

It's funny watching Keith run back and forth in the back...lol.

PHENOMENAL!!!

Thanks so much for the positive feedback. Stay-tuned as we will have another video coming in a few weeks👍

Thank you, James

Kevin, thanks so much. I work with a great group of guys @Trained By Techs and it’s a tremendous team effort. We will have plenty more instructional videos to come 👍

Thank You, I can’t tell you how much we appreciate the feedback. It’s a good feeling, to know my articles are helpful.

L1 Automotive Diagnostics and Programming LLC good tip will try this

I wouldn't, potential for blowing your scope if its connected to ground some how such as when connected to a mains powered laptop as you're effectively creating a short through the scope. Battery powered not as risky. Safest bet just use the invert function.

Why what happened?

@@TrainedbyTechs he only quick smirked even though I walked by mooning him . 😏

@@NewLevelAuto 🤣😂🤣

haha he actually did I was there xDDD

AWESOME! This is exactly why we share! So many have helped us, early in our careers and we wish to pay it forward

Thanks Cuba , appreciate the support ❤️

Thank you!

Invert the probes....that is simple and brilliant! Awesome tip. Will try that next time :)

😆..I love those clowns, great friends

Yes, I had to give him a lollipop just to get him to sit still😆

Yep Me too! I definetely want to see a compression waveform from the civic wich has 20 some PSI difference in relation to other cylinders...

Most-definitely...lets pool our collected data and I will do a follow-up video-post

THANKS, More on the way! Anything you’d like to know more about?

Dustin, thanks brother 👍

Thanks for the reply Mike. AC Coupling will remove the DC from the circuit and simply show the "change" in voltage. Everytime a piston approaches TDC, the voltage will naturally drop due to the load on the circuit. AC coupling allows the scale of the tool to be much smaller (1-2v) which allows the drops in voltage to be more pronounced in appearance. Effectively creating a "zoom" feature.

Brandon you are the man. Thanks for the explanation!

Surely, Typically we view waveforms as reference to ground.When we view an AC signal, we think of it as one that varies above and below the ground line (meaning positive and negative). This is a true statement but it would be more accurate to say “an AC signal is one that varies above and below the reference point. When we AC Couple a Waveform, we make the reference point the average point or center of the waveform (not ground). If we then place the scope in a lower voltage range, we can view variations above and below the reference point (the average of Waveform. This technique serves as a ZOOM function. This works well on scopes that don’t possess great zoom capabilities. Does this make sense?

Thanks for the input and I’m glad we could assist you 👍

Yes, the vdrop Test will yield you similar results as the amperage-test. Close enough to make a sound determination of a mechanical fault

Voltage drop and current flow are proportional to one another. In fact, You You place the both on the same scope, they are mirror images of one another , just inversely proportional

Better than that...I challenge you to try it yourself, on a known-good vehicle. Capture/post and tag me in it...tell us all what the test has shown you 👍

Brandon Steckler I see what you’ve done there and I like it, it shows how professional and committed you guys are to teach us 👍... unfortunately I don’t own a scope but I’m setting some goals for 2019 and a pico scope is one of them hopefully soon ... cheers

You be sure to let us know how we can help you move forward

You are not off the hook yet, though… When you get your scope, I still expect your capture/post 😬

Hey Michael, You bring about a great point. The terminology “relative” obviously referred to how each current-peak relates to the next. Because is inferre s “starter-Load”, minor/normal variations in compression won’t make much of an effect on the current-trace. However, when there is enough of a shift in compression-differential to cause a drivability-symptom, my experience has been that the evidence is clear. Try it yourself, by loosening a single spark plug to simulate compression loss👍

@@brandonsteckler3417 Brandon, I was trying to find out if anyone had ever tied the two tests together. In other words would a 10% reduction in compression over the companion cylinders show up in a relative compression test, OR would it take 20, 30, or 40 percent before you'd see the difference on a relative compression trace? I was looking for the cutoff number?

I would assume it’s based upon the the vertical-resolution of the scope and would also take an accurate/responsive supplemental-voltage support, to maintain the accuracy of the test

Bill, this is true. To sync the RC test, a second channel is needed.

Thanks, you can clearly see the value in the test. Most-often the faults it reveals can be seen when the engine is cold. However, there could certainly be situation ms that arise where a mechanical fault will surface when an engine comes to operating temp. My advice...test under the conditions the “symptom” is present 👍

Hi, Great question. The key to successful and efficient diagnostics is understanding the limitation of the tools/tests being utilized. The relative-compression test (voltage-drop or amperage) simply displays the the load placed upon the starter as each piston, in-turn , completes a compression stroke. So long as the cylinder fills/seals similar to the other and has the similar stroke, the load should be the same. To answer your question, simply having oil on the spark plug means oil consumption is present but not necessarily a loss in compression. Does this make sense ?

Next day....i got it! Awesome test, thanks!

Awesome! Yes, the test comes in very handy. The best part....it’s quick/easy , yields a ton of data and can be applied to virtually all DC-motor started engines👍

Yes! Thank you for pointing that out. Anywhere there is access to source voltage/Ground can be utilized. The DLC is a great place to sample, right from the driver’s seat. You make the valid point of capturing a sync only if a fault is detected. It definitely saves time not to find a sync unless necessary. I appreciate your help, thank you!

Now this is the kind of extra info I love

Armando, my friend! Thanks for tuning in. We’ll get together one of these days! Thanks for the feedback!

Jesse, so true. Thanks for bringing that point up👍

APP is a request, not a command. Depending on the software/strategy, the throttle blade mat not open