Jeep 4.0 Misfire waveform

Joseph Technician South Carolina Posted   Latest   Edited  
Unsolved
Driveability
2000 Jeep Wrangler Sport 4.0L (S) 5-spd (NV3550)
P0306 — Cylinder 6 Misfire Detected

Hey Everyone,

I posted about this issue on the other forum and got some pretty good feedback regarding common problems and TSB's for misfires on these engines. But this one is giving me the business. I have some other captures I need to make but if anyone has any idea what is happening here I will take a silver bullet at this point :)

Scanner will only count on cylinder 6. The capture is taken during the misfire something seems to be happening during injector turn off. Also why I have neglected to mention other testing done because there seems to be an anomaly happening. 

I pulled the cam sensor and found the dummy shaft had play in it so it was replaced thinking that it might be causing an issue with injector turn off.

Sorry about the short post I will add more captures and any other information.

Labels might be hard to read Channel A is injector and coil current taken from the fuse. Channel B is number 6 injector voltage.

Thanks,

Joseph

I should have mentioned that when the vehicle isn't missing all the injectors look like the first 2 in the capture with a definable cutoff during the injector portion

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Louie Instructor
Illinois
Louie Default
 

It's not a anomaly. It's normal. You have both injector and ignition waveforms on at the same time.

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Paul Mechanic
Illinois
Paul Default
 

As last as you understand you are looking at both injectors and coil current, the coil current is overlapping into injector current due to ignition timing changing/adjustment. I would like into valve timing(chain) slop as well as ignition timing components. Are you syncing off of cylinder 6 injector?

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Joseph Technician
South Carolina
Joseph Default
 

Paul, Thank you for the advice, I think you may be right about timing chain slop as I can't think of anything else that would allow a change in dwell within one fire cycle. But then again it just could be me trying to see something that isn't there, it's kind of my MO :)

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Ray Diagnostician
Ontario
Ray Default
   

What is the engine vacuum? The 3 captures are from a 2000 Jeep 4.0 The first GIF is a good injector/coil amps at idle In the second GIF, CH B is the ckp, CH C is the cmp and CH D is a pressure transducer in the intake while cranking. One cylinder has a repeating weak vacuum pull. In the third GIF, CH A is the coil 1 primary volts, CH B is the coil 2 primary volts and CH C is the coil 3…

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Joseph Technician
South Carolina
Joseph Default
 

Ray, Thank you for all of your captures, here and everywhere you post them, they have been extremely helpful to me over the years I have been all over the truck with the scope after the scan tool seemed to not give me the direction I was looking for and I feel that I had covered most of my bases. This was the only thing that I could see that was different from when the misfire was occurring…

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Ray Diagnostician
Ontario
Ray Default
 

Joseph, happy I could help you and I appreciate the feedback.

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