Ignition Coil Current question

Nathan Owner/Technician Ohio Posted   Latest  
Updated
Electrical
2011 Ram 1500 Laramie 5.7L (T EZH) 5-spd (545RFE)
P0303 — Cylinder 3 Misfire Detected

Hello everyone thanks for taking a min to read this. what I have is a Intermittent misfire which I could not duplicate on test drive, however there was p0303 stored in the PCM. I hooked the pico up to Cyl 3 and 5 voltage and current. cylinder 3 is blue and red traces. I guess this is kind of a stupid question but why does the ignition waveform look good but the coil is obviously Shorted. The waveform is at idle. would this be a example were it should of been loaded like cranking or power brake? or would it never show in the ignition voltage waveform unless the misfire is present?

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Matthew Mobile Technician
Illinois
Matthew Default
 

Could your current probe polarity be reversed on cylinder 3? If that is the case, it may not be shorted, instead it could be a breakdown in the secondary.

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Nathan Owner/Technician
Ohio
Nathan Default
 

You are correct it is up side down ill get it warmed back up and re test.

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Bob Diagnostician
Belarus
Bob Default
   

How is it "the coil is obviously Shorted"? current looks reversed. interesting current flow of 2 amps after the firing event (just like maybe open in the secondary and current have no where to go)

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Nathan Owner/Technician
Ohio
Nathan Default
 

It is reversed re testing now.

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George Owner/Technician
Alaska
George Default
 

This is the 1 with the dual spark plug? Maybe only half the coil is shorted. Did you pull the plugs? I didn't really look at the waveforms as it's hard to see anything on my phone. I ran into this once where only 1 side of the coil was firing and not very well.?????? To prove it I pulled the coil and hooked up spark testers. I had a weak intermittent spark on 1 side and no spark at all on the…

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Nathan Owner/Technician
Ohio
Nathan Update
 

hey fellas thanks for the help I can not duplicate the waveform with the clamp turned the right way. I must of had the clamp touching something else or something.

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Dmitriy Analyst
Ontario
Dmitriy Default
 

Nathan, this is interesting, what is the model of the amp clamp used?

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Nathan Owner/Technician
Ohio
Nathan Default
 

Pico

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Matthew Mobile Technician
Illinois
Matthew Default
 

I would do a long relative compression test, and scroll through the data closely, in case you have a broken valve spring...

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Ray Diagnostician
Ontario
Ray Default
 

In the Freeze Frame, is the rpm at idle or at WOT? In the freeze Frame, if the code set on a cold start, the problem could be a head gasket leak. This capture is from a 2016 Challenger 5.7 and cyl 1 misfired at WOT. CH A is COP 1, CH B is starter amps, CH C is a FLS in the intake and you can see a repeating low vacuum pull.

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Interesting
Glenn Owner/Technician
Texas
Glenn Default
 

i would change the time base and look at the turn on and turn off oscillations. there appears to be a tail at the turn off point, but not clear enough with the time base your on to tell anything. I would definitely do the relative compression test.

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Tim Mechanic
Arkansas
Tim Default
 

Ray, forgive me for asking, but was the issue a broken intake valve spring on your capture? The low portion of the waveform appears to happen when the pressure is supposed to be rising, so I was thinking a broken valve spring on the cylinder that is on the power stroke could cause this. Please let me know because I am attempting to learn these.

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Ray Diagnostician
Ontario
Ray Default
 

A used car lot had just purchased the car and they were hoping that the misfire was caused by a low priced coil or injector and they did not wish to spend money to disassemble the head.

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Tim Mechanic
Arkansas
Tim Default
 

Ok. Thanks for replying!

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Stephen Technician
Tennessee
Stephen Default
 

Tim, My interpretation is that the low pull is cylinder 1. Cyl 1 has the highest amp pull on compression so a leaking valve would not seem right. I too see that it is when the pressure should be rising. Because the valve duration is much longer that the 90* “window” that the FLS can see and valve overlap, I think that the main information available on a FLS intake capture is the opening of the…

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Sean Technician
Ohio
Sean Default
 

ray, every time I have the time to go through and read my emails and past post. I find your responses, and Albin's so informative. Its great you guys share so much with very little thank yous even though they are probably very thankful.

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Ray Diagnostician
Ontario
Ray Default
 

I'm glad that you find my posts informative, happy to help.

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Stephen Technician
Tennessee
Stephen Default
 

The burn line for cyl 3 has an “anomaly” just part center. Kind of like the s… got blown out? Cyl 5 has a better looking burn line. I also wonder why cyl 3 coil has current limiting but cyl 5 does not? And why does cyl 3 current have a flyback effect but not cyl 5? Are both coils OE?

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Matthew Mobile Technician
Illinois
Matthew Default
 

I don't think it is current limiting, the current probe was backwards and he selected current probe in the channel settings. When you select the 20 amp probe, it clips anything below -5 amps, so you are seeing the waveform clipped there.

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Agree
Brian Instructor
Ohio
Brian Default
 

Hi Nathan , I am way late to the party here. Also I am still learning secondary ignition patterns. Just wanted to make sure you know that you can easily compare patters by adding scope view , setting horizontal zooms the same for each view and adjust offset to line them up. diag​.​net/file/f7e8k5ulw…

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