In Cylinder Waveform

Bruce from Spring Hill Technician Posted   Latest   Edited  
Discussion
Driveability
2005 GMC Sierra 1500 5.3L (B L33) 4-spd (4L60-E)
P0300 - Random/Multiple Cylinder Misfire Detected

2005 GMC Sierra 5.3. We put an engine in from GM and it got towed back in because it would barely run. Had a Mass air flow performance code and a P0300. Scan data showed misfires on cylinders #1 and #3. My first mistake was not performing a relative compression test. I went after the misfires on #1 and #3. Cut the story short, I put the WPS in cylinder #3. It showed a very high running compression and vacuum on the exhaust stroke. And what looked like it started building pressure on the compression stroke immediately. 

After chasing my tail for a minute I performed a relative compression and found cylinder #2 was dead. It had to go to the dealer for the repair, due to their warranty. They found a broken exhaust valve spring. This pic is in cylinder of #3 with the broken exhaust valve spring being on #2. 

ETA-Thought I would also add that the total fuel trims were -40% on both banks.

This image is the in cylinder of #3 after the repair, looks perfectly normal.

+8

Ray from North York

 

Diagnostician
 

Good work Bruce and thanks for posting the wave forms!

Ray

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Bruce from Spring Hill

 

Technician
 

Thanks to whoever edited my post​.​lol Made it better

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Scott from Claremont

 

Manager
 

You’re welcome! 🙂

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Josh from Lynchburg

 

Technician
 

So #2 must be on intake stroke while 3 is on exhaust? 

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Bruce from Spring Hill

 

Technician
 

That's my guess but I haven't put an overlay on it yet

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Bill from Rosetown

 

Technician
 

Hello Bruce,

Interesting waveform. Is there any way you could share that file for manipulation? I would really like to view it. I am unable to make sense of everything, Sometimes I need to play to have things sink in.

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Bruce from Spring Hill

 

Technician
 

I will add it to the original post. But it might be tomorrow before I can

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Bill from Rosetown

 

Technician
 

Appreciated.

Thank you.

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Bruce from Spring Hill

 

Technician
 

Couldn't figure out how to load the pico file here, But here is a link to it, let me know if it doesn't work for you

drive​.​google​.​com/file/d/1f6GiCw…

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Bill from Rosetown

   

Technician
   

Hello Bruce,

I think there may have been an acquisition error that caused some confusion. ChA was AC coupled during the capture and has caused some unusual activity. That should help clear up certain pressures during the capture. It would be difficult to make sense of the initial capture.

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Bruce from Spring Hill

 

Technician
 

Well that changes things. Thank you for catching that. I had my pressure pulse sensor on a Honda right before I went to help look at this one. I'll try to be more careful next time.

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Bill from Rosetown

 

Technician
 

You bet. 

It happens. 

If I see a similar signature during acquisition now I will know what I did.

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Scott from Claremont

 

Manager
 

Hi Bruce, FYI, we’re currently working on support for other file types and you’ll find difficulty in trying to attach it here today. Please email the file to … and we will figure out a way to add it to your post.

Thanks.

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Geoff from Lahaina

 

Diagnostician
 

I noticed that issue when trying to put a really short video on here. Even if the site can't embed the object class we should be able to attach it for download. Attaching for download would actually be better cuz it doesn't slow the page load for the rest who don't want to see it. In the broadband crazy world everyone forgets about load times. It can take 30 seconds for a page load some days here.

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Geoff from Lahaina

 

Diagnostician
 

I'm kinda the same way Bill. These always make perfect sense if I am walked through it, but are just a mess if I stare at one cold. Easiest to just have two goods, and one bad, so we can say "that's bad, open the engine, see you later" ;-)

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Bill from Rosetown

 

Technician
 

Hello Geoff,

I like to place my rulers/make measurements and find where all the events take place etc. Then I can tell exactly what happened by the capture. Maybe a personal preference.

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Geoff from Lahaina

 

Diagnostician
 

I haven't seen how to do that yet. I only see them already marked-up, which I understand perfectly, or totally blank, which are useless to me.

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Bill from Rosetown

 

Technician
 

You can grab the file and open it with the pico software. That way you can really get down to the details of pressures and valve events etc.

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Eric from Edgerton

   

Owner/Technician
   

Geoff, have you seen the video lessons put on by Keith Perkins? It is a good set of lessons on using the Pico software. You don't even need to have a Pico scope to download and use their free software. With the software you can download, view and manipulate files that others share here and other places. You can find them here: diag​.​net/msg/m38bz0gbw2… ,

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Geoff from Lahaina

 

Diagnostician
 

actually, they are all here, youtube​.​com/channel/UC6pKb… and not all by Keith, but yes, I watched them all. I talked to Keith about making one that does overlays, in another thread.

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