Odd Pico Plug Captures

Doug Owner/Technician California Posted   Latest   Edited  
Updated
Tooling
2000 GMC Jimmy SLE 4.3L (W L35) 4-spd (4L60-E)
Captures

Greetings All, I took these captures on a 2000 GMC Jimmy 4.3 showing the secondary plug waveform. My question is on the first capture why does in not show more “normal good” spark lines? They are not misfiring and they show this on all the captures. The other picture shows a jump in spark line and was wondering if anyone might have an explanation for it and if they get the same happenings. Doesn't matter which vehicle I do this on it always shows up periodically. 

I'm using a capacitive secondary not Pico probe. I will also take a picture of the King lead to add later. 

Thank you for any suggestions.

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Glenn Owner/Technician
Texas
Glenn
 

Does your lead have a ground on it?

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Doug Owner/Technician
California
Doug
 

Yes

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Jorge Manager
California
Jorge
 

Doug, If this system has a dist and a coil wire then you best signal will be picked up at the coil wire. The scope will pickup all cylinders in a parade. To ID the cylinder in question, use another channel to connect a secondary, or actual trigger pickup, to cylinder #1 and reference the firing order data.

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Ray Diagnostician
Ontario
Ray
   

CH A is the secondary lead on the coil wire and I'm doing a brake torque. CH B is the primary coil winding voltage. CH D is a sync probe on the cyl 1 plug wire. The Sample interval should be set to 1 us to scope ignition. Use 500ms/div and 6 MS.

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Sherman Owner
Texas
Sherman
 

The inside the cylinder event is extremely lean. Also, several of your plug lines are above 18KV. Is this idle speed? Either way, the high KV demand points to a VERY lean issue. I haven't seen that pattern in years. My memory fails me as to just what is wrong. You can find Mac Van DenBrink on You Tube in his EXTREMELY knowledgeable “Through The Eyes Of The Scope” I think he teaches that example…

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Steven Mechanic
Washington
Steven
 

I remember the old black secondary ignition leads that came with the old picoscope kits would do that. Then they came out with updated secondary ignition leads that were colored (blue, red, green, and yellow), and that was supposed to fix that problem. I don't know if the updated leads did indeed fix it, because I still have the old black ones that came with my kit when I purchased it long ago…

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Doug Owner/Technician
California
Doug
 

Yeah I've been using older Hantech leads. I need to purchase some Pico ones!

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Grant Technician
Illinois
Grant
 

Steve, you appear to be referring to the Autonerdz colored leads that have different attenuation. Pico only offers black secondary leads in my experience.

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Doug Owner/Technician
California
Doug
 

I ordered one and will be updating on any difference. Yes it is black.

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Steven Mechanic
Washington
Steven
 

Oh, I didn't realize it's an Autonerdz product. Do you have them? Are they working good for you?

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Grant Technician
Illinois
Grant
 

I'm happy with them so far. Can't say I'm an expert with ignition though. I bought them a year ago after watching Spence De'Corde's Group Therapy presentations on Secondary Ignition. He shows the difference between the Pico Secondary leads and the Autonerdz colored secondary leads…how he prefers the colored Nerdz leads due to less wandering on the voltage line. Spence shows how the wandering is…

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Doug Owner/Technician
California
Doug
 

I recently purchased a new blue pickup lead and have a capture now of both leads and the differences I will show soon.

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Doug Owner/Technician
California
Doug
 

Yes Sherman I think I've watched him before I will look him up thank you!

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Doug Owner/Technician
California
Doug Update
 

I'm in the process of putting some coil capsures together. The misfires happen quite a bit on cylinders 4, 5 and 6 when cold, after it warms up it runs really good!! Has been doing this for a long time. I also noticed that the map sensor is only 5.7 PSI!

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Glenn Owner/Technician
Texas
Glenn
 

MAP at 5.7 Hg. is way too low. You said PSI? These later models had a high rate of intake gasket failures.

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Doug Owner/Technician
California
Doug
   

Yah it should be at least 10 to 16 right? Last year I checked for intake leaks but didn't find anything! I forgot to check the fuel trims but will do that, Thanks Glenn.

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Glenn Owner/Technician
Texas
Glenn
 

Hi Doug, During a cold start, use a spray bottle of water and spray the intake mount areas with a stream of water. Watch for excess steam coming out of the tailpipe and listen for a possible gurgle/ sucking sound. These intakes are bad about leaking and have to be torqued exact when replacing intake plate style gaskets. Ultimately, it may need an intake replacement. The 5.3 and 5.7's also had…

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Doug Owner/Technician
California
Doug
 

So the actual vacuum is 18.5 to 19.5 psi. So I need to get another MAP sensor! Fuel trims are good. And it didn't take much to kill the motor by sucking on the MAP sensor!

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Glenn Owner/Technician
Texas
Glenn
 

Hi Doug, That sounds like a MAP or bad line going to it. Usually a MAP should test good at 18-20 Hg of vacuum from what I have seen.

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Doug Owner/Technician
California
Doug Update
 

Here are the updated Coil captures. Tomorrow I will take them again when its cold and has the misfires. I already have changed Cap and Rotor (AC Delco Cap), and switched plugs and wires but with no change in misfires.

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Doug Owner/Technician
California
Doug
 

Here is the misfire updates although it is empossible to see anything worth anything with these poor captures! 4, 5 and 6 were misfiring a lot. I will present a capture after I receive the new secondary Pico pickup lead.

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Ray Diagnostician
Ontario
Ray
 

There is at least one cylinder that repeatedly has no spark arcing across the spark plug's air gap. Do not use secondary leads on distributor type ignition system plug wires. Use the secondary leads on DIS plug wires. Compare all of the plug wire KVs and all spark plug burn times using the coil wire secondary or the primary coil winding voltage. Purchase a Trigger Pickup Inductive Lead to…

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Doug Owner/Technician
California
Doug
   

I do have one of those inductive clamps also. I was wondering if they woukd give a better picture or not. I'll have to try that. Thank You for your time!

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Doug Owner/Technician
California
Doug
 

So the other one is capaciive pick up and was wondering why it doesn't work so well on distributor wires?

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Ray Diagnostician
Ontario
Ray
 

Another method to find cylinder 1, is to ground the cylinder 1 plug wire, with a jumper wire. In the coil wire secondary parade, you'll see 1 plug wire with low kv demand. Another method is to connect the GM ST125 coil output/spark tester into the end of the cylinder 1 plug wire. Or use an adjustable spark tester set to 25kv and the cylinder 1 secondary will show higher kv demand with a…

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Doug Owner/Technician
California
Doug
 

Thanks Ray. But at idle I can see number one spark. But I do need to play with the adjustable spark tester to see the difference in the KV of the coil for practice

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Ray Diagnostician
Ontario
Ray
 

My alternate method of locating the cylinder 1 will still work at all rpms and under all loads.

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Michael Owner/Technician
Alaska
Michael
 

If you are using the black secondary ignition leads, they will do that. I have had the colored leads do that on rare occasions. usually relocating the pickup on the wire will help

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Doug Owner/Technician
California
Doug
 

Those colored pico leads aren't clip over secondary leads are they?

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Ray Diagnostician
Ontario
Ray
   

The Autonerdz coloured secondary Pico leads will clip over the DIS secondary cables,

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Doug Owner/Technician
California
Doug
   

And they are superior to the black leads correct? And shoo you have a link to that please?

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Jorge Manager
California
Jorge
 

Doug, the pico leads with the clip also have a box at the base of the clip - it is 10,000:1 calibration. The picture of the leads in Ray's post are 1000:1 The colored leads are available in 9 different colors and the clip is designed to work with larger wires and down to 8mm. If you are worried about the lifting of the signal clipped to #1 plug wire, the best and ideal option is to use an actual…

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Doug Owner/Technician
California
Doug Update
 

So I replaced the MAP sensor with no change in output. I scoped the signal wire and there ihss none! I have yet to check it at the ECM and I'm going to do that next. The odd thing is that at wide open throttle it shows more vacuum than not! But I guess that kind of makes sense because the signal is not there. It does have 5 V Reference and a ground.

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