2008 Hummer H3 Misfire Case Study (Part 6)

If you do not see any other part of this series, you need to at least watch this one.
Here is the playlist for this series https://www.youtube.com/playlist?list=PLAFYVCyenqcoTvkbvE6avGuLJOQnFcx4Z
In this video I cover details that were missed in the cylinder pressure and intake vacuum waveforms from earlier videos in this series. The Picoscope really shows its abilities in this final before the repair video. I will do one more after the fix for you guys, so keep an eye out for it.
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consaka1 says:

Darn. I really wanted to see the deficit valve and seat to get a visual to go along with all the graphs and scopes.

Corky C says:

Paul,  This is really a great tutorial.  I enjoyed every minute of the discussion and can’t wait for more.  I wasn’t a fan of scopes, but this is an amazing display of what they can do if you take the time to analyze what you’re looking at.  This is great stuff!  I appreciate your time and tenacity on this problem.

Steve Scott says:

I’ve watched this case study multiple times and I see more detail each time. Gone are the days of the grease monkey and a good thing it is too. Over here we have heater plugs in diesels that double up as in cylinder pressure sensors

Ron Mcleod says:

Great video Paul, I have had a blocked drivers side CAT on a F250 V8 petrol, When I put the WPS in the cylinder and the pressure on the exhaust stroke was huge, from memory they got as high as 50 PSI at WOT so you never need to remove the O2 sensor to check the pressure again…. 

Chad Jessup says:

Good stuff as usual.  During the power stroke, combustion pressure will also escape through the defective intake valve into the intake manifold.  If I understand the pico traces, that increase manifests itself.

Joel Automotive In action says:

sorry I mean later retarded valve opening 

Kris Ankers says:

Cheers for the video Paul. I’m pretty sure you can see the leak on the exhaust stroke as well keeping the pressure high. If you use the pressure waveform to give yourself a rough idea were the piston is in the cylinder as a graph it would help to visualize the valve opening time. If I get time ill get a screen grab of your video and post an example. If you remember back I pointed out the pocket on the verus but the detail on that scope didn’t really give me confidence.

daveS ministry says:

Good demonstration on using scope to try and figure out this problem. Not much time saved except for relative compression showing which cylinder was at fault. Without the information from the hummer tech would you then also have to remove the valve cover and verify the valve lifter was not allowing the intake valve to completely close. Sorry for more mechanical work needed, before condemning the intake valve. If this were a commercial job and you took it down and did a valve job, you could have the same problem when you were done. These students are going out into the real world. Keep going you are doing a good job.

freeride202 says:

Great Job!!!

saltforddriveschool says:

Hi Paul. Always love your stuff. Regarding the start of this part 6, I think one would need to be careful of studying comparisons on relative compressions by doing an amp probe starter current relative comp test when you also have a pressure transducer in the suspect cylinder. The removal of the spark plug to replace with the pressure transducer increases the TDC cylinder volume and reduces the max compression available on that cylinder so a good cylinder would also be expected to show a max starter current and therefore cyl max pressure reduction. Maybe I’m missing the point at the start of this video but we can identify which cylinder relates to the starter current trace from the ignition pulse but the in cylinder pressure transducer just throws a spanner in the works.

Previously you had shown that cyl 4 was only slightly less compression ( but apparently enough to cause misfire) and that was a good comparison because all cylinders were left intact and the same. A starter current cylinder relative compression test when you have altered the suspect cylinder volume is not so useful for diagnosis to identify possible low compression and might draw the wrong conclusions. When we are investigating methods to reliable diagnose compression problems we need to be careful to make true cylinder comparisons. Best regards Brian

contagiousFX says:


If it wasn’t for the map sensor or vacuum waveform to compare with the pressure transducer, how would you identify that the valve is leaking on that pressure transducer waveform?


Tom N says:

I wish my scope had that type of filtering.

BBS_Robski says:

yes I’m on both Paul,good to see you experimenting with the in-cylinder pressure transducer technique, do you have a FLS (?) it would have been nice to see it on the inlet manifold along side of the WPS in cyl #4 or in fact the PV350 too 🙂

mike r. says:

i like relative compression signals to show map signal change which is more drastic in comparison to the others and the drastic change causes the next map event to show up less as the map sensor pressures try to recover from the flood of pressure. amazing what you are doing with electricity.this stuff is life changing when diag time and confidence meet. your premium channel is a must have tool. each time i view a video something always hits me that maybe didnt the first time viewed.

Shawn Lockard says:

I bought a Pico, You sold me on it. Thank you for all your help.

BBS_Robski says:

without looking back were the towers leaning on the leaking cylinder ?
Also just to point out when using a sensor ground make sure it isn’t a ‘floating’ one !

Saqib Khaliq says:

Awesome work, thank you so much. Want to see the head off to see the actual problem.

boptiludrop2020 says:

This a very good class and very well explain. The pressure going negative is a very good observation to show the valve leak. However the best tool would be to have a pressure volume curve calculation but picoscope seems not to have this feature for plotting this type of graph because you need to input several parameters for calculating the volume of the cylinder but it could be done externally by exporting the data and entering the information on a matrix.

Don Gamble says:

So, Paul, when the intake valve first opens the exhaust valve is still open due to overlap and when the piston is 90 degrees ATDC the stroke is moving at it’s highest velocity and then the lowest pressure will occur. How is that repair coming? Who is doing the work?

Darren Zinman says:

the noise on your sync is a freebee showing the EM pulses from the other cylinders.

sivaraj palanisamy says:

Paul awesome. To be honest with you I don’t think i aligned with you on previous part, what I thought is what explained in this video. Great man you are proving me that u don’t just read theory but would like to expirement theory and make it practical with evidence. I can bet you will go ways up in ur field. Thank you very much and I like to donate ur account. Can u pls message ur account to donate. I feel guilty to watch all ur hardworking without a penny to spare.

Steve Guest says:

Hi Paul,I’ve watched all 6 episodes of this and found it very helpful if not somewhat confusing at times lol but really eye opening and very interesting…..Many thanks

Rod X says:

In video 5 you said you will take the readings on the replacement head. It would be interesting to see what the MAP looks like with the re-worked or replaced cylinder head. looking forward to part 7 “The day After”.

John Fountain says:

Thank you for all you contributions on here 
Just one consideration having done experiments with my pico and in cylinder pressure transducers over the last year or so when you add the in cylinder transducer the volume of the hose from the spark plug hole to the transducer  lowers the compression ratio slightly so one often see a lower current draw on the cylinder with the transducer ..John 

Philippe Breault says:

Hi Paul, how did this ended? Have you done map or pressure transducer waveforms from the repaired engine?

bleachinuri says:

Thank you mr.danner it’s good to see someone like you sharing you knowledge I know I am learning something. If you don’t learn something new everyday then you didn’t have a good day

Jesus Malagon says:

thanks Danner

campen777 says:

Fantastic video and info , shame customers don’t appreciate what we have to learn just so we can fix there car .

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