2008 Hummer H3 Misfire Case Study (Part 5)

Here is a link to the other parts https://www.youtube.com/playlist?list=PLAFYVCyenqcoTvkbvE6avGuLJOQnFcx4Z
In this video I revisit the in-cylinder psi transducer test using my Picoscope in hopes of being able to ID a known valve problem. You will understand why I shot Part 4 of this series after watching this one.
Click here to watch part 4 http://youtu.be/oFCPeqPKGNU
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Alta9610 says:

It has to be a way to catch this problem with a scope!.. what about trying cylinder turbulence with secondary ignition wave forms?

sivaraj palanisamy says:

All this years i was under impression incylinder pressure transducer is the only one which shows all, but todays iam worried thats not the case.. i had this unit and have not used it yet.. but sure one day i will be back after refreshing my memories.



phantom explorer says:

I know its nothing to do with scope testing, but you should see high h.c with a gas analyser at idle maybe over 2000 h.c at idle ,and if you take the revs over 2000 rpm when misfire starts to get better h.c will fall to a more normal level, I used to see this when doing emissions test on older cars with worn valves pre cat days ,not sure how this would work on cars with cats  maybe you could try this on the hummer, steve uk

BBS_Robski says:


Tom Smith says:

I think the best thing you can do Paul it take the heads off and do the valves, give it a run for 500 miles and try it again 🙂   Fred UK

Lee Wilson says:

Interesting stuff

Kilian Berreth says:

The famous ScannerDanner OVERKILL.. Loving it…I too am curious about the First Look transducer. Engines just being air pumps what goes it should come out….I seem to remember an old school test for valve problems where you would hook a timing light to one spark plugs at a time. The strobe action of the light would catch the offending valve in the open position…Never used it but always remembered it.. 

timbo19751975 says:

Was there an outcome to the Hummer ???

Thomas EXOVCDS says:

Good to know that old school tools can still be of use on newer engines with all their electronics… I’ve been worried for years that I don’t have enough diagnostic equipment to troubleshoot modern engines. Glad to see that “checking the basics” still holds true!

brettless80 says:

Have you checked the cranking compression on the other cylinders eg. 123 and see if the low compression on No.4 is where the issue is.

James Thornton says:

Is there a function on Pico so you can trigger at a target RPM. looking at 5 as target and 4 as target. I know you are trying to keep variables to zero. You are keeping two cylinder miss looking at cyl # s Four and Five. If it was a Ford with spout rpm hold. That would be good but this is GM.

BBS_Robski says:

@ James Thornton
when a reference waveform is displayed on screen it can be aligned by using the delay function that is selectable from the bottom corners of the screen the same as vertices zoom.
As for a trigger I suppose if the advanced triggers were played with it may be possible but I’d stand corrected.
When using the zoom functions etc it’s not gospel that the value in the box has to be used, you can of course type your own values.

DJDevon3 says:

Yeah sorry about my comment in the last video.  After so many parts I forgot it was more about learning different methods to detect the issue.  Good old leak down test is still king.

DIAG kar says:

Paul I think that detecting leakage from outside cylinder is better than from inside one because pressure leakage is much lower than total compression that ‘s why it s difficult to make a decision according to WP500 sensor graph especially when it is a constant leakage. I propose to use sensor outside of cylinder chamber.

John B. Kobberstad says:

Lot of bad focus. Maybe have to borrow James’ new video camera. Otherwise great video.

Markymark24 says:

+ScannerDanner I’ve had a 2006 Hummer H3 a while ago with the valve issue and I’ve confirmed it with the leak down test, and out of curiosity I’ve checked it with my WPS500 and the pico @ cranking/idling and like you I didnt see much that could confirme the issue but I did it with a snap test and that’s where I saw a considerable rise in pressure for the intake

Lynx Star Automotive says:

The Pico is amazing. About time I get one. Why did you create a second misfire Paul? To offset the cylinder 4 misfire?

martin arrieta says:

give us some clases how to use the scanner

Second Wind Music says:

It was pretty subtle but cyl #4 had a larger vacuum pocket than #5 at the end of the power stroke in the cranking test.  It seems that if the a valve were leaking, during compression some air in the cylinder would be lost.  So at the end of the power stroke there would be less air in the cylinder than there was at the start of the compression stroke so there would be a higher vacuum at BTC than in a non-leaking cylinder.  I think that is exactly what we saw.  I don’t believe it shows during idle because ignition of the fuel provides enough pressure to fill the BDC volume.  Does that make sense?

freeride202 says:

The cranking waveform does indicate a leak.  First, obviously the low compression peak indicates a problem but the dip after the peak verifies a leak.  The overlay shows cylinder #5 with much less of a dip.  Basically, a certain amount of the original volume in the cylinder was lost during compression.  Now when the piston returns to BTC, a vacuum is created due to this loss.

I know this does not indicate were the leak is but I believe it rules out other possibilities like a bent connecting rod.

ShiversRSS says:

I love how you are analyzing this from all these angles with your scope. I’m surprised the pressure transducer test didn’t show much difference between cylinders. Looking forward to the fix video.

Chad Jessup says:

Just finished watching all five videos.  Question:  Why not place the spark probe on #4 so that a sync with the MAP pressure could be obtained?  I think that way, a small decrease in pressure could possibly be observed upon that bad hole firing when some of the combustion gases escaped through the defective intake valve into the intake manifold.

I am not surprised that the miss does not show up a high rpm, because the volume of air rushing through the intake system would vastly overwhelm the small amount of  combustion gas escaping through the defective intake valve.

I am a heavy equipment mechanic who works on SI engines maybe once a year, but I follow your videos with enthusiasm, as they are quite educational.  Keep up the good work!


Cool – I think I could relate to the MAP wave forms better than the pico transducer.  It seems the MAP was more obvious than the pico but I’m way to green to be able to use these techniques  with any degree of confidence. 

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