Ignition Coil Current question

Nathan Owner/Technician Hillsboro, Ohio Posted   Latest  
Question
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
Bartlett, 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
Hillsboro, 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
Vitebsk, 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
Hillsboro, Ohio
Nathan Default
 

It is reversed re testing now.

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George Owner/Technician
Skagway, 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
Hillsboro, 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
Toronto, Ontario
Dmitriy Default
 

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

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Nathan Owner/Technician
Hillsboro, Ohio
Nathan Default
 

Pico

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Matthew Mobile Technician
Bartlett, 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
North York, 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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Glenn Owner/Technician
Houston, 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
Blytheville, 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
North York, 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
Blytheville, Arkansas
Tim Default
 

Ok. Thanks for replying!

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Stephen Technician
Gallatin, 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
Cincinnati, 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
North York, Ontario
Ray Default
 

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

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Stephen Technician
Gallatin, 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
Bartlett, 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
Parma, 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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