HOW RELATIVE COMPRESSION TESTS CAN FOOL YOU

Thank you all for tuning in to Super Mario Diagnostics!

That's right, don't be fooled into going into the wrong diagnostic path by what you see in a relative compression test.
There are several things that can affect restive compression readings, this shows only one of the possibilities, and is not meant to be taken as the only thing that can affect RC tests.

I feel it's something that is not spoken about nearly enough when dealing with failed relative compression tests. Thank you for taking the time to watch!

The Taurus video mentioned:

I hope you all enjoy, like, share, comment and subscribe!

[VoltageDropDiagnostics]

Great video Mario. I agree, a failed RC test could easily send you into a wild goose chase. This is a good point you made because it isn’t talked about often.

[sollykhan]

Thank you for the time and trouble of posting this valuable educational video, yes often the gremlins can be miss fueling or water in the tank, or cheap fuel sourced from unreliable sources (junk yard) customers are not always very upfront or truthful in dissecting the core issues that could be resolved fairly quickly, i cannot understand why some car owners will use any narrative to sway the diagnostic procedure, misguided by a degree of vagueness and in asserting ignorance hoping that will bring about sympathetic results and a cheaper price! 🤔

[High_Tech_Mountain]

As ScannerDanner says there’s always variables. Great video Mario. Thanks for sharing.

[JoesAutoElectric]

Great video! I agree with you on being careful man. This point is not brought up nearly enough. You know my thoughts on fuel contamination LOL

[Usmanthemecano]

Here the importance of following notes. I now write down down all possible possibilities when diagnosing no start and go thru them chronologically. Sometimes you just forget... Nice tip

[BigDogDiagnostics]

Great video, definitely something to keep in the back of your mind. I could see that being overlooked very easily. And would not be a fun rabbit hole to travel down! Thanks for all the great content. I’ve learned so much from your videos, keep it up man!

[OzMechanics]

Brandon Steckler had an awesome case study with the same issue. Cylinder wash down screwed the compression

[killer]

It amazes me how people manage to do that (fill a gasoline car with diesel). The size difference of diesel and gas nozzles prevents people from putting diesel in a gasoline car. But as the saying goes, "If you make something idiot-proof, someone will just make a better idiot"

[mikea.]

Mario, thanks for your video, great info on the cylinder walls getting washed down.
Had a BMW come in.. So much time spent on it.. If we could get it running, it actually ran fine after warming up.. The way it was figured out that there was diesel in the gasoline was by accidentally spilling a little bit of it on the ground and realizing that it wasn't evaporating...

[codysautodiagnosticsprogra]

Great advice and example bro. This could have easily thrown even a seasoned tech for a loop.

[orville]

What a great video it shows that you never know what a customer is capable of and the never ending things that can enter in to diagnostics thanks for sharing.

[arthurfricchione]

New subscriber. Older DIYer but just learning scopes. Have many years of mechanical background but but self teaching with techs like yourself, Paul Danner, Keith Defazio, SMA, Cody diagnostics, PHD Ivan leading the way. Thanks for sharing. Artie 👍

[Matbug]

More and more cars coming in with diesel in then. I never thought it might influance a RC test. Thanks for the heads up!

[jimthecarguy]

Quick and easy when you know what your doing. Nice video

[guayaco-dmvu]

Excellent tip Mario..
Something to keep in kind for any future similar issues..

[billyyoder]

Thank you Mario. Good job. I appreciate your videos. Have a blessed and safe week.

[power]

GO MARIO, IT LOOKS LIKE IT'S BEST TO ADD A FUEL SAMPLE TEST IT CAN'T HURT THANKS AND PLEASE KEEP UP THE GREAT WORK !

[macknumber]

Subbed...you are a good mechanic giving good advice

[jasonc.]

😱😱. Awesome Mario. Very useful tips. I know I would've been down that wrong path. But not anymore thanks to u 😇

[MH-wobe]

I see a lot of gas in diesel (vs here was diesel in gas) and a couple things I have seen when the two are mixed. Gas obviously has a stronger smell so you can smell it when it is not supposed to be there. If you put a little of the mixture on your fingers (just a drop or two) it will be a little oily. Where straight gas will not and straight diesel will be really oily. Lastly put about a teaspoon of the mixture on a workbench, when it spreads out you can watch the gas evaporate out of the mixture and you will be left with just diesel fuel. That will give you a good idea how contaminated the system is.