Secondary Ignition Lab Scope Testing

Carl Technician Baytown, Texas Posted   Latest  
Discussion
Electrical
1988 Ford F-250 Custom 5.8L (H) 3-spd (RAT-FF)
Misfire

Why is my labscope only showing 6 cylinders ? and some of them are dropping out.

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Rich Manager
Lincolnshire, Illinois
Rich Default
 

Go into setup and select 8 cylinders if you haven't already. It looks like it is not detecting all the firings. The display trigger on the lower toolbar right side likely needs to be lowered. My rule of thumb is to set it at the average spark kv to start out and then adjust if needed. The level it is at is marked by the right facing triangle along the left side of the grid. The ignition display…

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Carl Technician
Baytown, Texas
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found it. had to back out of pre-select menu and go into utilities to set cylinders... Thanks Ignition looks good. I need to check injectors for leaking. It has a new EGR so do not believe it leaking.

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Jim Mobile Technician
Southampton, Pennsylvania
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Great advice, Rich

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Carl Technician
Baytown, Texas
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Will current ramping injectors find leaking/dribbling injectors or do I need to pull the rail and visually inspect?

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Jim Mobile Technician
Southampton, Pennsylvania
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Carl, What I generally do is, If possible, monitor the fuel pressure after shutting down the engine, then remove spark plugs and use my exhaust analyzer at each of the spark plug openings, the cylinder or cylinders with a leaking injector will be much higher HC reading.

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Gary Owner/Technician
Buena Vista, Colorado
Gary Default
 

Pretty crafty diagnostic strategy, Jim. So how have you been doing?

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Jim Mobile Technician
Southampton, Pennsylvania
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Doing Good, Gary. Was looking for you at Vision ? STAY SAFE, My Friend.

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Gary Owner/Technician
Buena Vista, Colorado
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I had some health issues for the past two years. Nothing serious, just made it inconvenient to travel. Of course now, the Corona Virus has everything and I mean EVERYTHING screwed up. So I'm now in lock-down mode with the covers pulled over my head... {:0(

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Jürgen Owner
San Cristóbal de las Casas, Mexico
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Current ramping will not show a leaking injector. Current ramping will reveal electrical conditions of the injector circuit and/or injector windings. While it will also indicate some mechanical problems like a pintle that is not moving at all, it does not show mechanical details like a not properly seating pintle. You might detect a weak spring inside of an injector by the voltage trace: the…

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Ray Diagnostician
North York, Ontario
Ray Default
 

The spark plug on the left is fuel fouled. The fuel is acting as a conductor for the spark to travel up the center insulated terminal into the spark plug body, to ground. The spark plug on the right shows the spark arcing from the center electrode, thru the air gap, to the plug's ground terminal, which ignited the cylinder's air fuel mixture.

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Ray Diagnostician
North York, Ontario
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Carl, you can also scope the coil primary winding voltage to check the spark plug's burn time, for rich or lean injectors. This capture is from an '89 Mercedes V8. The blue channel is the coil primary winding voltage and the spark plugs are firing for 1.8ms The red channel is the coil primary winding amperage draw The green channel is a sync probe on the cyl 1 plug wire The tan channel is…

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Helpful
Gerardo Owner/Technician
Wapato, Washington
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Hi I have a question, How those cylinders look to you. Good or bad? I'm new to the Labscope and I'm Learning

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Ray Diagnostician
North York, Ontario
Ray Default
 

The capture that I posted is known good

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Dennis Owner/Technician
Plymouth, Michigan
Dennis Default
 

Besides setting to the number of cylinder you also need to select firing order at least you have to on my verus.

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Ray Diagnostician
North York, Ontario
Ray Default
 

This capture is from a 89 Ford v8. The blue channel is a secondary probe on the coil wire and there are several misfires caused by carbon tracks. Note the spark plugs with no burn time and the spark is not arcing from the plug's center electrode to the plug's ground terminal, to ignite the air/fuel mixture. The red channel is a sync probe on cyl 1 plug wire.

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