How to Diagnose Misfires Right from the Power Distribution Center

mrrsm

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Normally, I would cover anything related to the use of ANY Oscilloscope over at THIS Link:

https://gmtnation.com/forums/threads/how-to-use-pico-2204a-hantek-1008c-oscilloscopes.20423/

But with a contemporary issues in Recent Threads involving a P0014 (and a P0016) as well as a P0306, THIS Video affords Us THE PERFECT Opportunity to Answer the Question:

“Can We Diagnose our COPS (Coil Over Plugs) AND Our EFIs (Electronic Fuel Injectors) at the SAME Time, WITHOUT HAVING TO REMOVE ANYTHING FROM A RUNNING MOTOR? ...Right at the Power Distribution Center?"

Yup…! (Well... Perhaps One, Little Fuse...) :>)

And HERE is WHY…

Take a look at THIS Partial Diagram (Screen Print) of the GM 4.2L LL8 PCM-to-Engine Bus Harnessing for the COPs and the EFIs. Notice how they SHARE A COMMON POWER SOURCE ONLY ON THE PINK WIRE(s)?:

LL8ENGINEWIRING1.jpg
Next … We can observe how they ALSO Share Only One Fuse in the Power Distribution Center:

Fuse #28

LL8ENGINEWIRING2.jpg

So… If We remove Fuse #28 and transpose in a 'Fuse Buddy' (Red Wire Loop) with a 15 AMP Fuse installed…

FUSEBUDDYLOOP1.jpg

We can encircle the Red Wire Loop with a Low Amperage 'Amp Clamp' and after Plugging the Tool’s BNC Connector into any Open Channel of ANY Oscilloscope (No Attenuator Required)

...
and after "Zeroing Out" the Amp Clamp, We can then read the Wave Forms as Low Amperage Draws (Converted as Voltage Over Time to Amps within the Software and by making the correct Tool Selection) and Discover:

"What is Happening?"

within the Pink Wire(s) leading from the PCM to ALL of the COPs and ALL of the EFIs at the same time:

FUSEBUDDYLOOP2.jpg

Now… by looking at the Combined Wave Forms on Screen:

LL8COPSNEFISFIRING1.jpg

...We can see that the Taller Spikes represent the COPs Firing Line:

LL8COPSNEFISFIRING3.jpg

....We can also see a Missing Tall Spike along the Firing Line of the Coil Over Plugs:

LL8COPSNEFISFIRING2.jpg

...and if you look at the Shorter, adjacent Spikes... We can identify WHEN the EFIs are Firing:

LL8COPSNEFISFIRING4.jpg

….and since we have a P0306 Code… Have a Look at THIS Image and Count the Sequence 1-6:

LL8COPSNEFISFIRING5.jpg

As you can see… We can instantly observe The Absence of a Primary HV Spike at COP #6...but perhaps even MORE Important is that:

NOW We Know WHY our Catalytic Converter gets SO DAMNED HOT and Why we will soon have to Replace it if We Do NOT solve "The Riddle of The Misfires".


And So… After Replacing the Inoperative COP… Please Observe the "Known Good Coil On Plug - EFI Oscilloscope Wave Form" for the GM 4.2L LL8 Engine Below:

LL8COPSNEFISFIRING6.jpg

Finally... We can Clear the P0306 Code with NO RETURNS as now, the Engine Runs Smoothly.

Please Observe the Source Video for this Pictorial Training Story:


And if anyone can think of a Better Way to perform these Combined COP & EFI Diagnostics on a Running Engine...By ALL Means...Do Add Those Ideas to This Thread! :>)

Automotive Oscilloscope Diagnostics... FTW
 
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budwich

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I bet this technique can be used on a number of issues depending on how "high" the "low amp adapter" is.
 
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mrrsm

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NOTE:

Of all the GURU Members we are fortunate to have here at GMT Nation... @budwich ... Understands Better than ANYBODY ... ALL of the admonitions and warnings I mention in the following paragraphs.

Yes... You Absolutely CAN perform a Wide Range of "Parade" Diagnostics.
For example, you can use either the "Heavy Duty" Hantek CC-650 Amp Clamp instead of the Smaller Opening Jaws of the Hantek CC-65 Version used above for Testing Relative Engine Compression "On Parade".

You can also choose the more expensive 1,000 Amp Version Amp Clamp made by Snap-On to handle the SERIOUS High Amperage Draw Readings directly from either the Ground Cable or B+ Positive Power Cabling right off of the Battery making "Heavy Duty" Power Delivery Diagnostics possible.

Those Amp Clamps will serve well and truly for performing these equally "Painless & Tool Free" Relative Compression Tests vs. Pulling Spark Plugs and using the Dry & Wet Pneumatic Cylinder-By--Cylinder Compression Tests.

If you want to know what the Compression Status of ALL the Cylinders are "Quick...But NOT Dirty" using an Oscilloscope and a High Amp Clamp are The BEST Tools for this Job.

The thing to remember is that you cannot damage your Oscilloscope during this procedure, as long as everything is hooked up properly in these conditions because you will be taking the readings by using an INDIRECT Method.

In contrast, the times that any Mechanic using His/Her Oscilloscope Equipment gets exposed to High Voltage when Diagnosing either Solenoid Style EFIs Firing or High Voltage Coil-Over-Plug Ignition Systems, creates the need to place a Hantek 20:1 Attenuator in between either a BNC Style 'Coil Paddle Probe' or using a Hantek Plug Wire Capacitance Pick-Up and its connections to the BNC Channel(s) Pick Ups on Your Oscilloscope.

In every case... the High Voltage MUST be Properly Grounded to the Engine to Prevent Damaging the COPs caused by those 'Tailing Oscillations of High Voltage' happening on the Secondary Spark Line side of these COP Ignition Events.

If you're working on a Running Engine and you get caught in between any of THOSE events... You won't want to make this mistake more than ONCE. Understanding Basic Electricity and Respecting the Absolutely Unforgiving Nature of "IT" is Paramount for performing Safe Engine Diagnostics and Preventing either Personal Harm or Damage to ALL of the often Very Expensive Equipment involved.

As Strange as THIS might sound... Most of the time... COP Failures occur because of Running an Engine under VERY LEAN Air-Fuel Conditions creates Poor In-Cylinder Atmospheric Conditions that Stress the Primary and Secondary sides of the Coils with Excessive High Voltage Electrical Oscillations.

These forces can cause the Secondary High Voltage to bleed back inside of the Primary Coils... and Destroy the Units. One Way or Another... High Voltage WILL alwyas Seek the Shortest Path it can Find ...to get back to GROUND.

Once you gain some experience with this... You will be able to SEE these events happening Right On Screen, thanks to using Your Oscilloscope.

Random Lean Misfire Conditions in ANY Engine are the 'Death Knell' for Coil-On-Plug Systems when they are NOT quickly attended to and dealt with by Solving the Underlying Problems of Un-metered, Un-regulated AIR to invade the Closed System.

The Flip Side of this problem is having COP Fail-To-Fire Issues that allows Raw Fuel to get Dumped into various Cylinders, washing Lubricant off of the Cylinder Walls, lowering Motor Oil Lubricity in the Crank-Case from excessive Raw Fuel passing the Compression Rings and ending up also becoming expensive "Catalytic Converter Killers", to boot.

For Standard Distributor - Style Systems sporting One Coil producing Single Wire Primary High Voltage under Dwell, using the Special Hantek Capacitance Lead allows the User to create a similar "Primary Coil Firing Parade" for either 4-6 or 8 Cylinders and THAT makes this Diagnostic approach even easier on Early Model Cars... AND it is fitted with a Proper Bolt-Down GROUND LEAD for this purpose.

I think THIS Topic may be worthwhile as my next effort for making a follow on "Training Guide for using an Oscilloscope during COP and EFI Diagnostics".
 
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