Using Alternator Voltage to ID a misfire

Bill Technician Saskatchewan Posted   Latest  
Discussion
GM Truck Tech Chat
2008 GMC Sierra 1500 SLE 5.3L (M LH6) 4-spd (4L60-E)
Misfire

A short demo of using alternator voltage to ID a misfire. The computer effectively picked out misfire number 3. Misfire was repeatable and consistent. I hooked up for demo purposes. Truck is a 2007, but did not see VIN M listed as an option in the drop down for that year.

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Bob Owner/Technician
Massachusetts
Bob Default
 

Bill, This looks interesting but can you add a little more detail. When you say the "computer" picked out cyl3 do you mean the Picoscope or your scanner? In the file I see a drop in the ripple voltage near the cyl 1 trigger. How does this correlate to the cyl3 misfire?

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Bill Technician
Saskatchewan
Bill Default
   

I apologize Bob, By computer I should have said the misfire monitor on the scan tool. Basically I am looking for a consistently low upswing in the delta voltage on a specific cylinder. I can I.D. number 1 to start by looking for the first start of upswing in voltage after the ignition fires. There is a latency in the voltage pattern that needs to be accounted for. It is a quick and dirty test…

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Bob Owner/Technician
Massachusetts
Bob Default
 

Thanks, I get it now. Have you done this on other vehicles? It certainly looks like a nice quick and easy test if it's repeatable.

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Bill Technician
Saskatchewan
Bill Default
 

It is super easy, and super fast. It usually works, but there are times that it looks like gibberish.

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Geoff Diagnostician
Hawaii
Geoff Default
 

Hmm. I wonder if you have just discovered the computer algorithm for Ford's (IDS) Power Balance test. :-)

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Bill Technician
Saskatchewan
Bill Default
 

I think IDS uses the crank signal frequency, but this is quicker. Especially if you need to try and find wires (not using ids)

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Agree
Geoff Diagnostician
Hawaii
Geoff Default
 

nothing quick about setting up a scope out here, I have to keep it packed away or it gets covered with dirt from the wind across the baron fields above us.

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Bill Technician
Saskatchewan
Bill Default
 

I bet. Maybe a little cart with a cover?

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Geoff Diagnostician
Hawaii
Geoff Default
 

The floor plan of this place has everybody constantly passing through each others' work space, so it's safer locked away. Super-cool method though.

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Spencer Owner/Technician
Pennsylvania
Spencer Default
 

Is there a concern of someone stealing if it was left out? It is a cool method.

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Geoff Diagnostician
Hawaii
Geoff Default
   

Spencer, More of concern of knocked over and broken then stolen. Commercial space costs more than residential in Hawaii, so we don't have much room in the shop.

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Spencer Owner/Technician
Pennsylvania
Spencer Default
 

I see. One thing I am blessed with is a lot of space. Previous shop was a bit tight so I kinda know where you are coming from. We have pleanty of scopes and they are used on a daily basics so they are out in the open most times.

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Geoff Diagnostician
Hawaii
Geoff Default
 

That's cool. The only shop-owned scope is the old MODIS. Nobody uses that. The rest of the scopes are mine, and they are all stored away. I kept wanting a better one, from watching all the videos five or six years ago, but after finally getting a PICO, I think I have used it ten times in two years. Most times it doesn't help, (it just shows nothing wrong), and the customer will never pay for…

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Caleb Diagnostician
Indiana
Caleb Default
 

Wow this is sweet man. Thanks!

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Spencer Owner/Technician
Pennsylvania
Spencer Default
 

Yeah it is.

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Bill Technician
Saskatchewan
Bill Default
 

You're welcome.

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