DONT TRUST THE RELATIVE COMPRESSION TEST!

[@freeride202]

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.

[@sollykhan2385]

well advanced for his relative young age, no doubt a very dedicated and enthusiastic tech heading to be the very best out there, well deserving the highest respects 😇👍

[@phillipzan2005]

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.

[@Stormin06096]

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

[@abraham01257]

I agree I learn something new, nice job Mario

[@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!

[@mattt4183]

Not using a sync can hide a bad bank. But you can catch it with the timebase. Normal cranking RPM is around 200 which is 600ms for 720*. If your waveform is taking a second or so to complete 720* but doesn't sound like a slow crank it's time to retake the capture with a sync.

[@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 !!

[@crasher88]

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.

[@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.

[@SuperMarioDiagnostics]

Can't say I've tried that, but then there would be no restriction between the intake manifold and the atmosphere, skewing the waveform

[@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-tn7vj]

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

[@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

[@SS-U23]

I did not figure out the setup for the pulse sensor. thank you

[@sollykhan2385]

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

[@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.

[@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 😅

[@JoseSilveira-newhandleforYT]

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

[@advancedleveldiagnostics]

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

[@SuperMarioDiagnostics]

Since my intake bladder is completely blocking any airflow, i needed some kind of metered airflow inlet to allow air to enter the engine

[@advancedleveldiagnostics]

@@SuperMarioDiagnostics Thanks!

[@danthecarman8440]

I would like to suggest to isolate a valve seating issue you could put some oil in the intake to help the valve seat a bit. I've had sticky valves causing me some real headaches and that helped me.

[@timothymohammed919]

Mario I would make the call "More testing is required" because I can see a loss of compression, The real question is where is it going, so pulse test Intake, exhaust, crank case and cooling system.... and once you find where the compression is going.... you can make a decision on what needs to be done. LOoking at the history of the engine, mechanical failure or abnormalities would not be a surprise.

[@nwadeswim]

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

[@bensiemers5094]

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.

[@SuperMarioDiagnostics]

Thanks The vacuum gauge has its place sure, just not in multi-air engines or bmw valvetronic engines, and likely several others that require a vacuum pump to run their brake booster since engine vacuum is near nonexistent

[@bensiemers5094]

Great point, Mario! All the very best of success.

[@richardnilsen5]

A great lesson👍 Brilliant😁

[@jeremyhossler2203]

I just ordered a bunch of stuff for my scope. I learned a little bit about the vacuum pulse test at vision this year and want to add this to every diag I do. Still working on my diag procedures.

[@eacherenkeka]

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

[@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!

[@franciscobadillo9451]

Could you please explain how is the connection of the pulse sensor in the throttle

[@jimcavanaugh6074]

Very good. Are you saying the intake valve perhaps is not opening fully or at all? Surprising that is not picked up in the RC test. I'm not a technician just a DIYer. What if you compression tested each cylinder independently?

[@truthsmiles]

I think it would be that it’s not closing/sealing. The graph is a bit confusing but for the red line “up” is closer to atmospheric pressure. So, my guess is on the compression stroke, whatever air was sucked in is getting pushed back into the intake manifold, bumping the pressure higher momentarily. And yes, if you do the good ole’ compression test I think you’d see a significant difference in that cylinder for sure. Techs use these methods because time is money and removing plugs is more time consuming, plus there’s always the risk of stripping threads or snapping a plug off in the head. Personally as a former mechanic but now just a DIYer, I use the standard compression test on my own and friends and families’ cars. I _might_ use the RC test on a car I was considering buying but I’d be embarrassed to do that on the kind of cheap cars I buy. So, when shopping I’ll just floor it and crank and listen carefully as he showed at the beginning. If it sounds even it’s probably okay, especially if it runs well. So, yes, I probably would have been duped by this car. It sounded nice and even (especially at the end), and I probably would have assumed the miss was a coil.

[@jimcavanaugh6074]

@@truthsmiles ah yes. That could certainly cause the pressure in the intake.

[@vinnymac01ss]

Can you show exactly how you set up the isolation from the crank case? Are you using a bladder from a smoke machine? Interested.

[@jmc6940]

The real master tech. Thanks for sharing.

[@GregoryBirulkin]

Should do a cylinder leak down test, then listen for escaping air.

[@themechanic6117]

Great lesson! Thanks Mario 👍

[@tonyedwin9042]

Is that an afm engine. Possibly be a bad afm lifter ?

[@mastmec]

Your last question, yes every 8th is a drop. But still would verify.

[@ganeshnarayan5505]

Great video thanks for sharing this useful information.

[@JeffinTD]

Great video. Assuming the heads came off, what was found?

[@AT-wl9yq]

Don't they have this feature on any of the high end scanners?

[@straydawg13]

Great video, I'm curious on if this test would still reveal a problem on the intake pulse if there was an exhaust valve problem? I'm a new scope user, this was super helpful info

[@SuperMarioDiagnostics]

You'd see a weaker intake pull for the same cylinder and that would warrant going into exhaust pulse testing

[@straydawg13]

@@SuperMarioDiagnostics Thanks 🙏🙏

[@laurpaicu4272]

Have you tried the relative compression test when engine is hot?

[@bernardaflores1720]

One more thing to add to the book of knowledge.

[@mikechiodetti4482]

Wow! Never saw that before. So the real way to do the RC is to have both an intake and exhaust sensors and of course the amp clamp. What I didn't see clearly was HOW you blocked off the crankcase. What was the final problem on teardown?

[@victorlarin9356]

What if the exhaust valve was leaking? Just wondering if an exhaust waveform is also needed to rule everything out…

[@prospexican]

you can perform an in cylinder test w a pressure transducer

[@ahwee77329]

crankcase insolate from the intake---sorry i am abit lost here -- can you explain a little more on these-- thanks mario as always

[@markferraro5250]

Great points Mo couldn’t agree with you more

[@arthurfricchione8119]

Mario thank you for sharing that info. Everything you share is helpful and good to know troubleshooting. Stay safe and well 😊 Artie

[@BesprovolkiSvias]

I do not think this intake pulse test will work on turbos. Can we still do reliable Relative Compression test on turbos? Or, perhaps turbo is not functioning yet at low crank RPM-s and we still can detect intake pulse?

[@calebbouchillon]

That appeared to be the pico low amp large jaw clamp. I can't get a usable waveform using it for RV versus my normal smaller jaw low amp clamp which I can set to 100mv=1amp. Why is that?

[@carguy1312]

great advice - curious though, what does one do with all of the new-fangled engines where you can't just pull the pcv hose due to being part of a valve cover or something?

[@sargetester99]

What if it is the exhaust valve and not the intake, it will show the same RC wave?

[@SuperMarioDiagnostics]

Yes it can

[@twostroke12v71]

Commenting on the video for the algorithm

[@secretsquirrel9722]

So, what was the actual fault with this car in the end Mario? Or did they not take it any further?

[@agoodneighborautorepair2176]

Very nice video,can you make a video using a relative compression and the compression transducer vs traditional compression gauges and vacuum gauge...Me encanta la manera que esplicas las cosas,you remained me to a friend that work with me in Honda dealear in Victoria Texas in 2004-05..blesssings

[@mike-yp1uk]

Would've like to see the cyl reference and fire order.

[@AutoDiag_]

Thank you very much for sharing with us

[@user-ky7ty3ie1x]

How compression test through spark plugs comperes ?

[@verajavi12]

Now do test on a turbo car

[@DerekJensen-m3q]

Mario is the tech I would love to be

[@wellingtonduran3148]

thank you mario for sharing that knowledge.

[@kbru78]

Thanks for sharing. how would you isolate crank case if it is one of those built on the valve cover?

[@donaldisrael7147]

Would cylinder leakage test have found the problem?

[@zaraahmad5618]

can you do in cylinder pressure transducer test on it ? for further diag?

[@ThunderbirdRocket]

Way to go ! Thanks !!

[@ousmanesarr7287]

Hey could you post the pico file of that relative compression and intake waveform please?

[@Muelli1000000]

Hey Mario, good Video! Could I also use the signal of the map sensor to log these pulses? Would be less effort and I don't need an extra pulse sensor...

[@SuperMarioDiagnostics]

Sure, but remember that's an absolute pressure sensor and isn't as accurate as a piezo

[@ws2664]

Did this actually throw a # 6 misfire code for a scan tool to read?

[@akaitv6606]

We use to use a vacuum guage to see valve issues.

[@terrybarkman3219]

Couldn’t you link another channel on the scope to a cyl then look at firing order to narrow which one is at fault ?

[@Grunter123]

😴

[@jimmyleung1194]

How about if exhaust valve if leak how u do test

[@amarabdelli487]

Thanks for sharing

[@jeffcompton6937]

Great video as usual

[@rafaelgarcia-xk7eu]

It looks like you have two hoses going into the intake tube. What's the other hose for?

[@SuperMarioDiagnostics]

To inflate the bladder

[@rafaelgarcia-xk7eu]

Okay, you didn’t mention you used the bladder. Now I get why you used the vacuum tee. Thanks.

[@brentcuffy8025]

I don’t understand how you deduced it was an intake valve issue from this test.

[@SuperMarioDiagnostics]

Adding a sync revealed that while number six was compressing, the intake pressure rose, indicating an intake valve leak. I show this technique here: kzbin.info/www/bejne/b2LaqqergZ2DnNE I learned these methods from Brandon Steckler's class

[@kurtblight1931]

I can't see how you setup your first look sensor. Do you have an easy intake installed in the intake tube?

[@SuperMarioDiagnostics]

Correct

[@autoemmissions3904]

What is an “easy intake”?

[@mitchellroberson]

Awesome video

[@sheerwillsurvival2064]

That’s awesome

[@oscarlorenzo206]

Hi Mario, what pulse sensor do you use?

[@SuperMarioDiagnostics]

I use the one from Cody on KZbin: Cody's Auto Diagnostics

[@carlosolvera72]

What if the leak was on the exhaust, I don’t suppose that would show on an intake pulse? Or am I wrong?

[@SuperMarioDiagnostics]

You'd likely see a weak intake pull during the number 6 induction stroke

[@carlosolvera72]

@@SuperMarioDiagnostics and that would be why I watch these videos thanks!

[@shamessun]

Wow 😮…… good video

[@timothykittle3165]

That looked like a ford 5.4 the heads need to be replaced

[@gumerasgarage5328]

I dont trust anybody, especially relative. lol

[@robertpope3619]

👍🏻

[@LSmiata]

Hello Mario, Liked the video. Relative compression test only one tool in the box but it gives a lot of info. I have BMW S85's with bent rods. Should be low compression on those cylinders do to piston not reaching TDC, but because of extra "drag" from a damaged bore can show high compression on the R.C. test. While "possible" it is hard to imagine the amp load being comparable to a "normal" cylinder. Bent rod would be low compression/low amp, more friction from damaged bore would record as high amp draw, or high compression. RC only one tool but simple and easy for a base point. Cheers and keep posting.

[@zackarymcclain164]

in my diagnostic process for drivability, I always start with verifying customer complaint. after I know it's present I typically go to a scan tool and do a full system dtc scan and review any data that might be relevent (fuel trims, misfire counts, freeze frame, etc.). the third step is the research phase, checking for relevant tsb's and troubleshooting information. usually, the first test procedure I will perform is a relative compression test to verify the mechanical integrity of the engine before we go down the rabbit hole of tests only to end up at a low-compression cylinder. I have started to really get addicted to my wps in the cylinder during a relative but I can see your point about using a deltap sensor. I need to start implementing the delatp sensor into my diagnostic process. not having the deltap sensor in the intake will only let you see whats going on in one particular sensor and cant help paint a more complete picture by looking at both.

[@SuperMarioDiagnostics]

Can't beat using multiple sensors, for sure

[@ismarmeskovic]

👍👍👍

[@mattt4183]

If you've saved that last RC only waveform put a link to download it in the description. I can't make a call based on a camera shot taken at an angle with no zoom or filtering on the waveform🤣🤣🤣

[@SuperMarioDiagnostics]

It was filtered and zoomed, and the camera shot is exactly like walking up to the screen using your eyes 😆

[@jakemartin4305]

Totally agree always verify mulitple was if at all possible if you can do 50 test (i know excessive lol) to prove your diag is 100% then do it im a firm believer in if you arnt gonna put your pay check on it then keep looking 😁👏👍

[@michaelt8330]

I'm curious did you buy any chance go in cylinder? I would think that if you had a intake valve not sealing you would have a leaning Tower.

[@richardcranium5839]

interesting

[@Mac-mu9cs]

In the end confirm confirm. I love RC test but never 100% trusted them. I have not advanced my own tools to do the pulse testing . Shop I worked at did not want to get that deep into diag. I strive to make sure im correct but as life is we will still get fooled but a little less after each leaning experience

[@Pablo_Automotive]

Realli nice, I remenber the another video and all complications It's because we are always alert with this kind of thing, thanks for share.

[@wagoosh78]

did the misfire stop as u increased rpm ? I was told a leaking valve seat can be over came . I watched a u tube video afew years ago on cold start a lifter wasnt bleeding down causing a misfire as engine heated oil thinned allowing bleed down so valve seated they used a in cylinder pressure transducer I dont recall if they did RC on the engine . keep the videos comming

[@SuperMarioDiagnostics]

It does improve with rpm

[@jackiemay9471]

trust no one as agent mulder said

[@mrfishbulb7187]

The truth is out there.....

[@mikem1014]

Nice BVro You Always teach us good shit love it man

[@nickayivor8432]

ACCOMPLISHED Super Mario Diagnostics 👍 🎶 🎵 👌 👏 My Mentor Super Mario Diagnostics Take care and have a great Evening with all your family around you PRODIGY Super Mario Diagnostics From Nick Ayivor from London England UK 🇬🇧 clock ⏰️ 22:48pm

[@keanMechanic]

Good advice chap. I would always check with a four gas, HC would have give it way.

[@1fnjo790]

Unless you have a car severely flooded car with all cylinders washed down ,I think you can pretty much trust relative compression test to at least tell a customer a tune up likely isn't going to resolve your problem. 😂

[@kyletuttle9064]

Great diag Mario thanks for sharing

[@lowridermig]

Great information thanks for sharing 👍