Single Cylinder Misfire/Compression Waveforms

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Single Cylinder Misfire/Compression Waveforms

Postby ScannerDanner » Thu Mar 15, 2012 10:06 pm

2001 Chevy Blazer 4.3 VIN W engine
Here is the history: Engine was replaced recently, misfire code P0300 present with #1 cylinder showing the most misfires. While watching live misfire monitor (scan data) the #1 is the only on that shows a misfire and it is slight. Only 18 misfires on average over a 200 firing event. Customer replaced cap, rotor, wires and plugs (all OEM parts) and it did not change his symptoms (I know these distributor caps have issues on this model, but this is the third one and I am pretty sure based on my Secondary waveforms that the ignition system is good). His complaint is just basically a little bit of a rough idle and a check engine light. Truck runs good when you are into the pedal.
So I looked at Secondary first and I see no problems. I did an injector balance test and all cylinders are identical. No vacuum leaks, internal or external. A basic vacuum test showed steady 19-20"hg at idle. No HC emissions in the cooling system (good headgasket). I believe there is a mechanical problem with this engine as everything else checks out but I am having a difficult time proving it. So as I am trying to learn and apply this in cylinder transducer tests. I took these capture and was wondering if any of you have any input on the results. Cylinders 4 and 6 are what we will call for now, the known good waveforms. I am using #4 and #6 cylinders to compare to the #1 cylinder that I think has an issue.
1mv=1psi for these captures
#1 cylinder cranking
2001 S10 Engine Propulsion_1.png

#4 cylinder cranking
2001 S10 Engine Propulsion_2.png

#6 cylinder cranking
2001 S10 Engine Propulsion_3.png

#1 cylinder cranking zoomed
2001 S10 Engine Propulsion_4.png

#4 cylinder cranking zoomed
2001 S10 Engine Propulsion_5.png

#6 cylinder cranking zoomed
2001 S10 Engine Propulsion_6.png

#1 cylinder at idle
2001 S10 Engine Propulsion_7.png

#4 cylinder at idle
2001 S10 Engine Propulsion_8.png

#6 cylinder at idle
2001 S10 Engine Propulsion_9.png

#1 cylinder at idle zoomed
2001 S10 Engine Propulsion_10.png

#4 cylinder at idle zoomed
2001 S10 Engine Propulsion_11.png

#6 cylinder at idle zoomed
2001 S10 Engine Propulsion_12.png

#1 cylinder running WOT snap zoomed
2001 S10 Engine Propulsion_13.png

#4 cylinder running WOT snap zoomed
2001 S10 Engine Propulsion_14.png

#6 cylinder running WOT snap zoomed
2001 S10 Engine Propulsion_15.png
ScannerDanner
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Re: Single Cylinder Misfire/Compression Waveforms

Postby Kev » Sat Mar 17, 2012 12:48 am

Hi Scanner Danner,
I can see where you are coming from with this Chevy, there's no obvious sign that I can see with compression. I would be very tempted to remove the injector from #1 cylinder and swap it with say #6 or one that's easy to get at! I would be interested to see if the misfire count on the data stream moved cylinders after this action. I understand that this doesn't demonstrate the pico scope, which is what the website is mainly about, but I would be very interested to see what the outcome would be!!

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Re: Single Cylinder Misfire/Compression Waveforms

Postby Darren Cotton » Sat Mar 17, 2012 12:39 pm

Paul

Can you post or email me the Psdata files...

Thanks

Darren
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Re: Single Cylinder Misfire/Compression Waveforms

Postby ScannerDanner » Fri Apr 27, 2012 4:14 am

An update on this truck. Owner stated he replaced the crank sensor and the misfire code is now gone. He stated the old sensor was rubbing on the reluctor. This would explain the misfire code for sure and also why I couldn't find a problem with the #1 cylinder. (or any cylinder for that matter)
My main concern in the waveforms I uploaded was the exhaust stroke section of the #1 cylinder looked significantly different than the other cylinders. What I learned (From John Thortons DVD) is, that section will be most affected by exhaust manifold design and where the cylinder is in that manifold. In short, it looked different because we were seeing turbulence from the other two cylinders dumping exhaust gas in the same manifold further downstream.
Hope that helps someone out there. Sorry for the delay in updating this.
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