DONT TRUST THE RELATIVE COMPRESSION TEST!

Thank you all for tuning in to Super Mario Diagnostics!

[freeride]

The regret Mario has by testing components in the wrong order for a misfire. Yet never changed a single part during the diagnosis. We need more techs like this. He his next level. This is from a 24 year technician and shop owner. Whatever he is payed isn't enough.

[Stormin]

Excellent job Mario. I like the tip about isolating the crankcase from the intake.

[phillipzan]

I had this happen to me. I now use a pressure transducer alongside an RC test. One note is when I went back and redid the RC test on the vehicle that burned me and cleaned up the wave form and zoomed in a little, I could see the low cylinder. It was small, but there.

[DTEAuto]

Definitely awesome information to put out, always great to hear things like this to avoid pitfalls. I swear you were going to say always use a sync and not miss a complete bank that isn't contributing when the firing order bounces bank to bank in numerical order.
P.S. I have had a hemi where I had the same looking intake pattern and my mind went quickly to leaking intake valve, naturally thought this since the intake pattern had a "rise" in pressure. But I ended up figuring out that the rise in pressure was from a "lack" of intake "activity" in the manifold from a bad lifter....i.e. meaning the intake valve opened late so the no action of pressure change in vacuum pull made the pattern rise until finally the valve opened up and it pulled down the pattern but from a higher-pressure starting point.
Thanks again as always for sharing!

[keltecshooter]

This is so awesome, i wish I could like it twice.
I had this experience a few months back, when I dug deeper it was apparent that the valves had been blasted but one particular cyl had the tiniest of leak on an intake valve.
It never occurred to me to do both tests simultaneously.
Outstanding content, I know I won't make this mistake again and it's so easy, minimal extra setup time and better results. Win win !!

[crasher]

I had a similar experience a few weeks ago with a car, can't remember the make or model. Did a relative compression test and saw the humps for each cylinder so I ruled out a mechanical problem and kept going on with my diagnostic. Lost story short I came back to needing to do a compression test and found extremely low compression on all 3 front cylinders, front wheel drive vehicle with a v6, ie 25-30 psi. I went back to my relative compression test results and now it stood out to me. The amp draw during starting was only 30 or 40 amps when it should have been 3 or 4 times that much. I only saw the pattern I was wanting and moved on. Didn't back it up with any physical data and got burned by the test. The test showed me what was wrong I just misinterpreted the data.

[jmc]

The real master tech. Thanks for sharing.

[bartscave]

If you can’t isolate the PCV system would simply opening the oil fill cap prevent false readings too? Thanks for continuing to bring us these videos Mario! They are always helpful.

[sollykhan]

Thank you for a an excellent tutorial, very educational and detailed, please post more, Bless 😇

[JoseSilveira-newhandleforYT]

This is a good and cautionary lesson! Thanks for posting it.

[AD-T]

This is why I’m going to the vision expo in March so I can learn these wonderful techniques from Brandon . Thanks for the lesson Mario 👍🏽

[DJ-tnvj]

Finally bro. Finally someone sees what I see from time to time. Got burn a few times with the RC test. Started doing more testing to verify before making the call. Thanks for the heads up

[driftwhat]

I watched this video before. I'm now watching it again. It so happen to be that I don't remember the message from this video. Wow what a refresher. I wish I can hit the thumbs up twice 😅

[nwadeswim]

Great job!...keep up the great work, you are an inspiration to always learn more!

[CameInStrong]

A good idea is to also tap into a signal wire for an ignition coil. When you do that, you’ll know what cylinder is which by the firing order. For example, you tap into cylinder 1 ignition coil signal wire. When you look at your scope readings, you’ll see a giant line. That line will show cylinder one. Then you can just read the rest of the pulses by the firing order.

[JoelAutomotiveInaction]

Great details and demonstrations 😊 thanks I do Rc, intake pulse & exhaust pulse, any cylinder spark one shot 😀 any way I have 8 channel scope

[advancedleveldiagnostics]

Great information Mario, Thanks! Can you please explain the Tee you used, how does that mimic a closed throttle?

[bensiemers]

As techs we tend to overcomplicate our diagnosis process and forget the value of simple tools, such as a vacuum gauge, which can efficiently point out compression and valve issues in seconds, among many other conditions including potential issues such as valve timing, exhaust restriction etc. Not to dismiss the value and power of scopes. Great video and advice.

[eurbanautotech]

Awesome video. I feel bad how much my pressure pulse sensor sits in my toolbox... I haven't used it enough to learn the nuances well enough so it tends to be neglected. If I'm pulling a spark plug on a vehicle with an inconsistent misfire then I'll pretty much always throw my WPS500x in there for a quick capture. That way I can stay fresh on in cylinder waveforms and have something to go back over later if needed. But I really gotta start using my FirstLook pressure sensor more... Thank you for reminding me about that!

[eacherenkeka]

Great information Mario! I will start following your advice! Thank you for sharing!