How to test for a plugged exhaust (picoscope and psi transducer) Part 2

[@derikhaaf4753]

I tremendously enjoy your videos, but what I also really enjoy is that fact that you're not afraid to admit when you are not sure about something or got something mixed up. Also I think it is great that you are willing to learn with your students and accept other people's advice/opinions. Its very difficult to find a good instructor that will accept advice or thoughts from a student. Thanks again.

[@MaciasDiagnostics]

I have a couple of high school students, I tell them all the time, no u tube editing shows the real case study results. Even seasoned technicians have situations that result in difficult questions. The training and learning curve never ends. Great training video.

[@michaelovitch]

4:13 Pipes lengths are different on banks 1 and 2. Bernoulli principle on fluids : When you increase a fluid velocity ,it's pressure drop. When you reduce its velocity ,its pressure rises. It would explain the two different patterns on bank 1 and 2 while it's clogged downstream. gases from bank 1 are quicker to travel,because the pipe is longer,so bajk 1 cylinder vacuum each other less well than on the passenger side,so you read more cylinder pressure. That's how you tune a header,by modifying pipes diameter and length accoring to rpm target to increase volumetric efficiency. I guess.

[@alexanderdavis1160]

Yes I 've done this with 3/16 brake line. Drill the 3/16, insert brake line, measure, then sheet metal screw as "Cap" suggested.

[@isaiaszaragoza9379]

I believe that the set up of the y piping sharing both exhausts banks could give those readings. Separating the exhaust banks and then testing you isolated the bad one.great job.we never stopped learning.

[@rustysuperbeetle3064]

Hello Paul Danner.... I was wondering if you had any videos of disabling the EGR by removing or plugging it hose, or disconnecting one of its control solenoids and taking a vacuum reading at idle and again at 2500 rpms? I have seen where you connected to the DPFE sensor. Is this a different scenario or similar to the one I am describing? Thank for any information in this manner... @ScannerDanner

[@IntheBlood67]

My 02 Ford Ranger had 5 cats And when my truck shut down my longtime mechanic was stumped. In desperation a youth who was a Ranger whiz got the cats unclogged and my truck is back on the road. A side note to all this is that I had previously had all 5 cats replaced(Supposedly) under similar circumstances with previous engine/6 cyl. edge! When I was informed that the cats were the originals, I knew I had been scammed BIGTIME!

[@PineHollowAutoDiagnostics]

Hi Paul, great case study showing how to use the scientific method (hypothesis, experiment, conclusion) to develop testing tools and pinpointing the exact problem! I was also thinking that the driver's upper cat and the first downstream cat were restricted until you showed the backpressure readings. At this point to complete this case study you could show us the running in-cylinder pressure transducer test on this fixed vehicle. Maybe some waveforms from other known-good vehicles at 3k rpm, with 4 cyl engines vs. V6 vs. V8 would be helpful in explaining the positive pressures on the exhaust stroke. I think Tobias Jonsson makes a very valid point about higher in-cylinder pressures on the exhaust stroke at higher volume air flow just because the exhaust valve itself (even fully open) is still the bottleneck (highest resistance in air flow) between the cylinder and exhaust manifold. The "curve balls" definitely makes the process of developing testing methods more difficult, but also more fun! Thanks for sharing so we can all learn together. Now I want a pressure transducer!!

[@PineHollowAutoDiagnostics]

Thinking about the two waveforms for a few days brought up another point at 5:30 when you are comparing the exhaust stroke pressures on driver's bank vs. passenger bank. On the pass. bank, which we can call a known-good, the pressure only increases as the piston accelerates upward and pushes the exhaust gases out past the valve, as Tobias pointed out. However, on the driver's side, there is an IMMEDIATE spike in pressure as soon as the exhaust valve opens!! This is the real indication that there is pressure built up in the exhaust manifold that is backfeeding into the combustion chamber. Then the piston pushes against this existing pressure, creating the second higher 20psi hump, like an additive effect. The in-cylinder pressure transducer test for a plugged exhaust seems most conclusive at high rpm, with any built-up pressure in the exhaust manifold shown as an initial positive psi spike as the exhaust valve opens. At idle the air flow is much lower, so a partially restricted system would not be as evident...

[@ScannerDannerPremium]

motoYam82 I am in total agreement, with you and #Tobias. I just checked one of the few other engine propulsion waveforms I have stored of a good engine running at 2000 RPM (don't have one at 3000) and it read 5.44 psi! This would be bad if we were in the exhaust. The bottle neck description seems to be dead on. Also the waveform I have shows the gradual rise, near the end of the exhaust stroke (like the ranger showed on the good side). Not the sharp rise at the beginning. Tricky waveform to analyze for sure. I am almost sorry I didn't have a better understanding of this before shooting this video. On the other hand it is fun to lean together.

[@mctobbsi]

ScannerDanner Premium motoYam82 My thoughts were going all over the place when I first saw the waveforms and was thinking how can this be. You know that there should be virtually no pressure at all in the exhaust so you kind of have your mind set on that. Then when you get presented with evidence on what really goes on it takes some time to readjust and think about what exactly is happening and where the meassurement is taken. It is nice you got it figgured out. I guess we will see some more of these waveforms as oppertunity comes! Keep them coming. I learn something in almost everyone of your videos and it is really fun to be able to talk about with other people!

[@joachimjohan1215]

@@mctobbsi bor du i norland?

[@mctobbsi]

Joachim Johan Hej, nej jag bor i Skåne :) Vad tänkte du på?

[@curtgirardin6093]

Hi - I just watched this video, I realize I'm a couple years late - but just in front of that third CAT (the first "shared" cat), you drilled two holes, one in each pipe heading upstream. Then you measured the back-pressure on each one, one at a time. Is it possible that the excess back-pressure was escaping out the other hole, thus showing zero backpressure? When in reality, if the other hole was plugged up, you might have seen backpressure in the third cat, explaining why you did not see backpressure in the passenger cat, but you did see it in the cylinder...

[@ScannerDannerPremium]

No, I plugged the other holes during each test, plus they were too small to make a significant difference.

[@prospexican]

do the back pressure testing w pressure transducer and see what we get on both banks. after repair just so we can see were we at.

[@brbr-qe9cy]

What if the 10 psi you're seeing on the passenger side(good), with your pressure transducer, is just the backpressure of the piston pushing air past the exhaust valve. The bad side reading 10 psi past the valve plus the additional backpressure due to the plugged precat. I'm guessing if you were to do the pressure transducer test with the y pipe off, you'd still see close to 10 psi on all cylinders tested.

[@prospexican]

hi, were to get the pressure transducer? any part #? o model? other thing, i tough i was a good technician because normally shops hire me to diagnose their vehicles, but the more i see the more i learn, and the more i know that im not as good as i tough i was 😅😁

[@samuelw8439]

Good stuff as always. Would be interesting to see a WOT comparison on this. In my mind a restriction would be more evident the more air thats drawn in. Thanks for sharing.

[@jeremyshanks6937]

The inner cylinder pressure could just be due to the velocity and volume of air exiting the cylinder? Great video though, it gets you to thinking in a different direction. The pressure measurement was taken inside the combustion chamber, which does change things when thinking of exhaust back pressure. I agree that more "Known Good" engine cylinder pressure values would add to the case. I really like the idea of checking and measuring anything and everything possible with a scope. The ability to save and capture screen shots in a graph form is much more accurate and educational than watching a gauge needed fluctuate. Keep up the great work Danner.

[@ScannerDannerPremium]

Jeremy Shanks Thanks Jeremy. Lots a variables with the in cylinder stuff that's for sure. I'm learning with you guys on these.

[@jeremyshanks6937]

Keep on.

[@prospexican]

by making 2 holes b4 the cat after the upstream cat, dont the pressure will release by one of the holes? i think you should clog one of the holes to do that testing? or it should not matter due to small size hole?

[@ScannerDannerPremium]

hole is too small to be a significant change. Thank you!

[@alekstolstoi]

hey Paul , whats the maths to calculate plugged exhaust using the measures from the picoscope??

[@mctobbsi]

I'm certainly no expert on this subject but how about a part of the pressure build up only occurs in the combustion chamber? I mean, it i still a rather small hole, and with quite high velocity, the "exhaust" gases tries to go out through the valve compared to the cylinder diameter. Can it be that a part of the pressure rise is because the air is having a bit of a hard time escaping the combustion chamber? Just a thought.

[@shawnlockard2370]

And maybe the exhuast valve opening late and closing early do to wear.

[@shawnlockard2370]

Shawn Lockard I do like the drilling holes. The mig repairs that in two shakes of the lambs tail.

[@ScannerDannerPremium]

Tobias Jonsson I think you are on to something here Tobias. Read my response to @user/motoYam82

[@bernhardlist9359]

Dear Paul, in such a case You should also check the pressure in the intake because it is the connection between both banks and as you mentioned valve overlap that can feed into it. I always go and measure all things. First in cylinder, intake, exhaust (normally just from the back) but with such an in cylinder test of course you have to dig in more. Btw, a worn exhaust cam or (bent)valves that dont open fully can produce some interesting results too. I had a shifted (176 degrees in start attemt) intake cam recently on a Jaguar V8 engine and without the WPS500 I could not have solved the puzzle. If you want those scans I can email them to you. Greetings from Germany, Bernhard

[@cobbysparks9891]

Hello Dan, what kind of rubber tip did you put on the pressure gauge tool ?

[@andrewthompsonuk1]

This video has had me wondering for a few days now. I really cannot rationalize why you have almost zero pressure on the passenger side when you clearly have pressure on the sensor while the exhaust valve is open. I cannot think through how this could be valve overlap or any other pressure feed from the bad cat. Was the injector disconnected on the cylinder during the test? Is the transducer linear or is it logarithmic? Did the drill make vibrations that cleared out the center cat? Your logic and argument through the video made perfect sense to me. Will it be possible to repeat the transducer test as soon as the front cats are replaced? Finally I thought OBD2 cars were meant to disable the fuel on a cylinder after too many misfires to save the cats?

[@ScannerDannerPremium]

Andrew Thompson Andrew, read my reply to #motoYam82I do not think it is overlap anymore (well not 100% sure yet if that isn't also a factor) Unfortunately the student wrecked the truck and it is undriveable, I asked him to bring it back to do fuel trim analysis on it, to learn to ID a plugged cat with trim numbers. Needless to say I am super disappointed.Not all OBD II systems shut off the injectors with a misfire. It has to be cylinder specific as well. Thanks Andrew!

[@andrewthompsonuk1]

Thanks, this keeps you thinking. These tests will be the way of the future as it gets harder to access various components.

[@James-fs4rn]

👍Could there be an exhaust crossover in the intake causing the pressure to be seen on the good bank? Thanks again!

[@ScannerDannerPremium]

no sir

[@prospexican]

excellent diag, and explanation.

[@yusuihang]

Another great video series. Really enjoyed it. So it appears that melted cat could clog exhaust but not necessarily effect cat efficiency (because there was no cat efficiency code)? I would have still been interested in knowing the inlet and outlet temperatures of the cats just as data points for reference. For example, if driver side cat showed "good" outlet temp, then it would confirm Paul's hesitation at using temperature as a test for exhaust flow.

[@jonathanleon4611]

Would u be a to somehow use a cam sensor to see the exact moment when exhaust valve open and compare that waveform to the in cylinder transducer waveform ?

[@ScannerDannerPremium]

jonathan leon If you knew exactly where on the cam sensor waveform that event was.

[@2secondslater]

Check wit a temp gun at before and after each cat to check the temperature delta prior to the back pressure test to gain an understanding of what temperature delta to expect from a plugged cat, that will save you from drilling holes next time.

[@ScannerDannerPremium]

Just uploaded a case study on this proving the temp test for cats has variables and is NOT a foolproof way to test for cat restrictions. www.scannerdanner.com/scannerdanner-premium-chapters/chapter-1-universal-testing-methods/587-2006-lexus-rx-330-low-power-no-trouble-codes-part-1.html

[@2secondslater]

ScannerDanner Premium has moved to my website Hey I agree with you completely that it is not a definitive method, it can be a good indicator of a blockage and if you want to determine the exact point of blockage, then the method you have used in this video is absolutely on point and accurate. It doesn't harm to take readings and build knowledge of what symptoms can occur. I will be making the order for your hard copy book once I get some bills out of the way and subscribing to your premium channel.

[@charleslarrimore6521]

Is your book still available And what is the price

[@ScannerDannerPremium]

sorry for the late reply, I no longer monitor this channel, my book is available from my website at www.scannerdanner.com In the future if you comment on my main KZbin channel "ScannerDanner", I do see all of those. Thanks again!

[@thinman8621]

Would have been interesting to move the transducer to other cylinders and see if the banks still test the same.

[@prospexican]

most likely they will read about the same unless cylinder compression not close to same between cylinders. thats what i guess.

[@Madmark50484]

its a shame you couldnt display the after fix pico readings. That would have shown the normal operating parameters

[@shawnlockard2370]

I was just thinking that a worned out valve train might cause a similar reading on the Pico

[@ScannerDannerPremium]

Shawn Lockard I also think there are other variables (as you described). But it definitely starts with driveability symptoms for sure. This thing would not go over 30 mph and was not misfiring.

[@Rod-uw8ud]

How about a thermal camera image before drilling any holes?

[@jesusmalagon4336]

Thanks Paul Danner

[@tigerksewsankar7667]

Great video thank you.

[@oscardiaz6361]

I also have that bayco light

[@jerrya27]

this is very helpful info

[@ahill007ny]

Great video!!!

[@keijokokamagi3648]

I think you got false readings, because all other holes upstream and same level should have been blocked while taking a reading from one hole, because otherwise the pressure has an escape passage.

[@ScannerDannerPremium]

the tiny holes drilled would not have effected the backpressure in any rea measurable way

[@joachimjohan1215]

DONT BE A PARTS CHANGER!!!!!!! :D

[@carguy1312]

Same goes for single dads - watching in 2023 Biden-economy - so just saying.

[@Goultek]

never trust valves