HOW RELATIVE COMPRESSION TESTS CAN FOOL YOU
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- เผยแพร่เมื่อ 20 ต.ค. 2024
- 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:
2008 FORD TAURUS P0300 DIAG & FIXh ttps:// • 2008 FORD TAURUS P0300...
I hope you all enjoy, like, share, comment and subscribe!
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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"
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.
As ScannerDanner says there’s always variables. Great video Mario. Thanks for sharing.
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! 🤔
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
I thought I was the only one that did that
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!
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
Great video Joe, yours was Pepsi BTW!
Brandon Steckler had an awesome case study with the same issue. Cylinder wash down screwed the compression
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.
More and more cars coming in with diesel in then. I never thought it might influance a RC test. Thanks for the heads up!
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.
Quick and easy when you know what your doing. Nice video
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...
Great advice and example bro. This could have easily thrown even a seasoned tech for a loop.
agreed....and when you go down that wrong path you never forget....in my automotive journey whenever the vehicle is changing symptions right in front of you it is best to take 2 steps back and really think about whats going on...
Luckily this lesson i did not learn the hard way, but it was pure luck. 😅
😱😱. Awesome Mario. Very useful tips. I know I would've been down that wrong path. But not anymore thanks to u 😇
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 👍
Much appreciated sir! Thanks for the sub, hope you enjoy!
Subbed...you are a good mechanic giving good advice
Customer questions 1 have you recently refuelled 2 how much fuel 3 do you have the receipt. Misfuel is massive effective questioning minimising Diag time.
Excellent tip Mario..
Something to keep in kind for any future similar issues..
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 !
Thank you Mario. Good job. I appreciate your videos. Have a blessed and safe week.
Well done Mario this was a good one for sure. What happens now that you found Diesel, what type of damage can or was done? Great job ... Jay
We cleaned out the tank, flushed out the line, cleared out the cylinders, did an oil change, and it was good to go. Luckily no rods were bent, no misfires afterwards, he got very lucky!
Thanks for watching!
So if diesel washed down the cylinder wall, and it actually ran like that, was there any immediate critical damage caused to the engine or fuel tank?
How did you handle the fuel system??
Did you, or COULD you directly jump power to the fuel pump with the fuel line off, running a hose from the pump to a fuel can to pump out the old gas? Did you have to remove the tank to clean it?
And what work did the engine need afterwards besides new oil?
Excellent video, another variable, great tips Mario!
Can you put link to related video in your description for us? I'm going to watch it, but it's nice to have quick link, because I'm slow...lol!
She's got power now baby, rockin' the diesel!
😂 will do buddy
I've experienced cylinder wash a couple times. I also used brake clean to try to start a car i pulled the engine apart and had to throw the pistons away because it welded the rings in the grooves
How do you do a relative compression? Did you disable fuel or ignition? It would be nice to see how you got those results to either see what the problem is.
I disconnected every injector. Not sure i understand your last statement. I was about to check fuel pressure since it ran with alternate fuel. When i saw green gasoline come out, i took a sample and confirmed that it was diesel.
Super Mario Diagnostics so even with injectors disconnected the compression was bad “relative”. I guess a lot of diesel in the oil too. Thx a lot for this good information. I have run across contaminated fuel but have never done a relative compression whit it. I will next time. This got me curious.
Yes an change was necessary as well. Compression was erratic between all cylinders depending on sealing. At times it would idle perfectly, other times crank no start. Definitely was interesting, a plena vista. Hey, thanks for watching buddy and taking the time!
Hey mario. I had a vw tdi fuelled with petrol/diesel mix. Wasted time on loads of test till i did a leak off and the fuel was yellow. Wish i had of videoed it. Cheers dave
Mario! que buen video en definitiva esas son algunas experiencias que dejan marca y nunca se nos olvidan, me había tocado gasolina y agua y provoca falla, pero gasolina y diésel no. Gracias por compartirlo!!
i worked a week once on 3.8 Buick with maybe a small amount of diesel in it, only complaint rough idle on start-up for a few seconds then cleared out
great video
wouldnt this wash all cylinders causing low amperage across the board?
and not cylinder specific?
Interesting.Thanks for the helpful info ! I thought diesel nozels won't fit in the filler neck? Or is it the other way around ? 🤔
Here in Miami it's the wild west 😆 I've seen them both have the same size nozzle. Thanks for watching!
Smart tips must be taken in consideration in ever RC or C testing
Very smart 👌
Great info, I have not come across that problem, but with some gas stations even there gasoline pump handles are green, I think BP is one of them.
I think I would've been caught going the wrong way on that one. Good job of staying in the diagnostic funnel. I think I'll subscribe to your channel. 😉
😂
Yup.........I would have lost time on that one. Unless you could smell it when hooking up a fuel gauge. I would have needed to ask for help.
Great video Mario! -Glen
SUPER MARIO DIAGNOSTICS ///
,,, when one or more pistons are NOT giving any compression. What would be the problems on the cars engine?
/// Do you have to replace the piston or the actual engine block is cracked inside that piston cylinder and have to replace the whole engine block?
Wow thats spot on bud.
Thanku loads
I have never smelled anyone elses dipstick. Haha Couldn't resist. Nice find Mario!
😂
Awesomeness 🙌💯🍻
I had a customer replace a 750,000 engine put it together same problem I went in
Turns out bad fuel
Recommend every one have a hydrometer in there box to test fuel
I did a video showing the test device
Great video mario
Great advice . You can never assume anything .
Cylinder wash would kill some compression but can it kill all of it?And diesel can wash the same way as gas?
Diesel is "thicker" than gas so it should keep the compression and maybe seal those rings even better?
The car will not run because it will wet those plugs and even if were dry it can not ignite diesel anyways.
Sometimes is very hard to detect fuel contamination especially if you are not familiar with diesel.
The fuel in the dipstick was from lots of cranking and the fuel would leak down past the rings at rest.If this car is gdi than would make the spraying of fuel worse if it ran leaner at start up.
The thing is that it was not 100% diesel so maybe thats why you had irregular compression values.
You didnt show the values on each cylinder.Were they low or some of them higher than spec?
Hope you like my comment.Really like your videos and im learning a lot with them.
Thanks Mario.
this is the very reason I use external fuel supply on drivability issues.....very simple to rule out fuel as an issue or in your case, the main issue!....great vid Mario.......
Basics basics basics 😉
hope you don't think I'm coming across as a "know-it-all" but in reality fuel quality is one of the most overlooked items....I just had a early ford 3.0L (flex vehicle) with positive fuel trims..and not really running constant....took a good fuel sample and did a alcohol content test (10% water, 90% fuel from vehicle) well it was at 40%....enough said.....once again great vid
Not at all, i understand you, i appreciate your comment buddy
100% AGREED !
billmck12345 if you don't mind me asking, what is your method for running on external fuel? I've diagnosed fuel misfires by running the cars on fuel cleaner through intake but sometimes can be a pain since the one I use has inconsistent spray.
Great tip my man.
great video Mario just wondering arent the nozzels at the pump fool proof? thanks
They aren't federally mandated. But at this point it's hard to say exactly whether it was the pump nozzle or filler neck that allowed for this to happen
Great video! Thanx...wish I could of had a better or at least a longer view of the RC wave...teased me with a quick glance lol👍👍👍
😂Sorry buddy! I can assure you, the entire capture was similar. Thanks for watching buddy!
This was very interesting. In the early days of unleaded fuel, the pump nozzle, and the car filler port, were a smaller diameter, preventing putting leaded fuel in an unleaded car. Do diesel pump nozzles have something similar? Thank you for sharing. Did I just give my age away? Haha
Haha I've seen them here be the same diameter. Guess it depends on the fuel pump
Great tip Mario and should help a lot of techs out there! 😀👍
Thank you sir!
Oh no that's not a diesel car,thx for sharing mario
I had a Rogue with Bad Gas last week. I should have made a video about it... Awesome tip BTW!
What a video man! Good information and thank you for sharing your knowledge! Tienes un suscriptor más! Saludos!
Muchisimas gracias!
How about cutting the fuel when doing the RC test
Great information thanks, yes i have seen this before only just last week i got call out to a workshop that i car went in for just a service when they went to start the car it crank very slow on a low battery it got wash down and we had almost no compression the fix was put oil down the cylinders and then the car started and after a few minutes the car was ok . This all happened because of a low battery. So yes your right be very careful with Relative Compression test .
Don't forget to change the oil! 😄 het thanks for watching buddy
Thanks for sharing your knowledge.
Wish I could work with you and learn a lot from you. What state are you from? Thanks for the tip!
Thank you! I'm in Florida
Thanks your knowledge is no cuestionable but you need to used the graphics to explain the problems.
Very interesting Mario, thanks for sharing bud 👍
yep it happens on jaguar a lot of the time a cold start rich running condition will cause a low compression on cylinders
Brilliant thank you. We see a lot of this in Europe.
Didn't see that coming good observation 👌
Wow... diesel.... great diagnosis and fix....
So if we do RC test with injectors sockets disconnected, can we have a reliable RC test?
Great video 👍
Correct
That's some great information Mario.
Hey Wyatt! 👋 thank you buddy, glad you find it useful. I hope all is well 👍
I’m on my way to the Taurus. Super Mario!!
Great catch, Mario! At 2:20 you mention compression math by ScannerDanner. Is it a reference to his video or some other materials? Thanks!
Yes, he does have a video where he gets a compression reading from one cylinder, and divides the amperage by the psi. So x amps per psi. Then using that he fills in the rest of the compressions based on their individual amperage. Not meant to be a precise calculation though, he does mention
@@SuperMarioDiagnostics ScannerDanner has videos on relative compression, but I can't find the "psi per amp" video :( Are you sure it's not Matt's video (first result searching "relative compression test psi")?
It's embedded in one of his relative compression videos. He doesn't have a video dedicated to this calculation
eric o and ivan did this also on the "TWISTED CAMSHAFT" ...remember that one Mario??? one of my all time fav
Must've been a gdi 😆 no i haven't seen that one, mind sharing a link?
Great share Mario. Nice job 👍
nice case study💪🏻
Good video with great advice.
Quickie... but good info there!
Holy Frijoles
Nice job. Mario
yes that a good tip.tks
Ok so I gotta ask. What is crazy about the wave from that made you wonder something else. ?? Thank you
The waveform represents the compression of each cylinder. This would suggest a mechanical fault since there are two cylinders with low compression compared to the other two. If you were to look at a good engine, you'd see even, uniform compression strokes.
@@SuperMarioDiagnostics yes that I see and understand. But there's 2 high peak And 2 low peak . Indicating 2 cylinders having a lower compression then the other 2.. but I guess you have to hear it cranking to determine if it really ran ruff and having cylinder imbalance issues.. thanks for the great diagnosis. Good call. Keep it up.
Crank no start 😉 plus i did mention that it didn't sound right
@@SuperMarioDiagnostics yes you did. Thank you . Great call brother.
Nice. That could easily be a huge time waste.
good thinking Mario....that would been an easy left turn....diesel....maybe that's why its called flor...I .....DA ! only kidding
Taurus bad starter with comutators that have higher resistance?
🤔 you watched the video? That would result in drops of current
@@SuperMarioDiagnostics I didn't watch the video taking a wild guess
Oh ok lol that ones one of its issues, open circuited solenoid
@@SuperMarioDiagnostics he got lucky with that hydrolock.
🤔🤔🤔great job !!!!
Mario did you get that link??
Haven't seen it, but I'll do that search buddy thanks
Hyundai Tucson P0173 Case Study Part 1 and part 2 over at south main auto...3 years old....I promise you'll love it....
Wow i have seen this case study a very long time ago lol, spot on!
Low compression in all cylinders?
Did ya finish the video?
Super Mario Diagnostics yes I did but I like to try to guess ahead of time and you and Ivan always throw me curvs I do enjoy your videos very informative
😀👍🏻