Misfire cylinder #4

Michael Owner/Technician Quakertown, Pennsylvania Posted   Latest  
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2015 Ram ProMaster 1500 3.6L (ERB) 6-spd (62TE)
P0304 - Cylinder 4 Misfire Detected

Verified cylinder #4 (and only #4) is misfiring via "which cylinder is misfiring" PID. More of a fishbite type at idle and will have more counts if you power brake it. First I started with a relative compression test. Sync is on #4 - blue trace at the pcm connector (access is terrible on this thing) Pulse sensor is the red trace. First thing I see is inconsistent firing voltage. Is this something to be concerned about?

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Harley Owner/Technician
Kansas City, Kansas
Harley Default
 

I think you have a tiny hole in a spark plug boot. I'm not good on scope, but I have a lot of experience with 3.6 in Dodge Grand Caravans.

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Albin Diagnostician
Leavenworth, Washington
Albin Default
   

The only thing I see with your ignition is you have the sample rate too slow to properly capture the event. I also see one cylinder low on compression too.

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David Owner/Technician
St. Albert, Alberta
David Default
 

I am not able to understand enough of your traces but I would move #4 coil with another to see if the trouble followed the coil. Maybe take a look at the plug too? It would have been nice to see some secondary ignition waveforms for me. What I do seem to see is inconsistency on #4 primary voltage making me think the firing is inconsistent.

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Dennis Owner/Technician
Danielsville, Pennsylvania
Dennis Default
 

Problems with cam and lifter wear on these. What is the mileage? I had both replaced on my personal 2016 with under 50K on it. It started to tick. No misfires yet. Is this one loud?

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Randy Diagnostician
Glendora, California
Randy Default
 

How many miles on this ???

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Michael Owner/Technician
Quakertown, Pennsylvania
Michael Default
 

81,000

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Randy Diagnostician
Glendora, California
Randy Default
 

Are the plugs original

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Michael Owner/Technician
Quakertown, Pennsylvania
Michael Default
 

Yes, factory champions.

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Clinton Owner/Technician
Concord, New Hampshire
Clinton Default
 

I had same thing on same van and it ended out being a burn hole in the spark plug boot. Was obvious once I pulled intake plenum and coil. You are right real bear to properly test. The one I did got a set of boots and spark plugs because of mileage and has been fine since.

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Ray Diagnostician
North York, Ontario
Ray Default
 

The inconsistent firing voltage is caused by the low Sample rate, also difficult to look at the spark plug burn times for misfires because of the low Sample rate. The transducer in CH B shows the repeating low pulse in cyl 4 caused by a worn cam lobe/lifter issue.

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Paul Instructor
San Gabriel, California
Paul Default
 

WE had one that the valve seat dropped- fortunately it was under factory warranty - Paul

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Randy Diagnostician
Glendora, California
Randy Default
 

hay paul How are you doing ??? this is randy from ASC . ran into your guys at the autologic scope class last month. send me a email would love to here from you . …

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Michael Owner/Technician
Quakertown, Pennsylvania
Michael Update
 

Pinhole in the plug boot. How did I come to this? I'll be honest that I'm not good at analyzing these waveforms to say theres an issue in the secondary without doing a visual inspectio on the coil and plug on #4 but based on what I'm seeing in my snap throttle test the burn line had a ton of oscillations. A secondary ignition problem, no?

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Clinton Owner/Technician
Concord, New Hampshire
Clinton Default
   

Ha, looks exactly like the one I had. Start of a pattern on these. LOL. Same cylinder even.

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Ray Diagnostician
North York, Ontario
Ray Default
 

In the first capture, the first ignition firing event has no spark time, so the spark is arcing thru the plug boot. In the other firing events, the spark is arcing across the spark plug air gaps to the plug's ground terminals.

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Michael Owner/Technician
Quakertown, Pennsylvania
Michael Default
   

Thanks Ray. How many captures do you typically get when analyzing misfires? Idle? Snap throttle? 3,000 rpm? Power brake?

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Ray Diagnostician
North York, Ontario
Ray Default
 

For ignition misfires, take the captures at the rpm when the engine is misfiring. I prefer the brake torque because the compression rises, which can force the secondary spark to find an easier path to ground.

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Richard Technician
Stony Brook, New York
Richard Default
 

Hi Ray, I like the brake torque method also, I usually power brake at … rpm. It makes it easier to see if the fuel is running out causing the miss. I also found hard power brakes make it looks like everything is misfiring. Have you found the same?

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Ray Diagnostician
North York, Ontario
Ray Default
 

Secondary can look confusing during the brake torque, on some makes. Try to capture the coil primary voltages, the coil primary voltages can look easier to diagnose. The first capture is an 07 F-150 5.4 at idle, with no misfires. The scope is on all 4 COPs on the left bank and you can save time by scoping 4 COPs at one time. The second capture is the same vehicle and I am doing a brake torque…

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Stuart Mobile Technician
Blue Island, Illinois
Stuart Default
 

I am having similar issue with a similar vehicle so I'm going to be paying attention if you don't mind​.​Thanks

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