In cylinder wave forms

James Owner/Technician Jacksonville, Florida Posted   Latest   Edited  
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2017 Ram ProMaster 1500 3.6L (G ERB) 6-spd (62TE)—3C6TRVAGXHE509793
Cylinder 2 Misfire

Looking for guidance on diagnosing this dead misfire. I have pulled valve cover and lifter, follower, and cam lobe looks good, spinning over to test valves appear to be opening. However when it runs, no popping back in the intake or the exhaust. No noises, I figures the intake follower had fallen off. Pulled it down and no the case. I am trying to learn to do the in cylinder diagnosing. I changed the files to pdf so anyone can open. Let me know if you need anything else. I am just trying to learn. First one is in cylinder for bad cylinder, Second is running, trigger off number 1 coil, and first look in intake, 3rd is non misfiring cylinder for comparison. 

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Albin Diagnostician
Leavenworth, Washington
Albin Default
 

It is always best if you upload the raw scope file, but from what I can see, in your in-cylinder capture, the intake valve did not open.

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Ray Diagnostician
North York, Ontario
Ray Default
 

James, your in cylinder compression reads near 300 psi? In my first capture, the engine is cranking and the tan channel D shows the in cylinder cranking compression of 77 psi. The expansion stroke has a deep vacuum pocket. The piston rings are fuel washed. The second capture in the green channel C shows the in cylinder cranking compression of 16 psi and the intake valve is not opening.

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James Owner/Technician
Jacksonville, Florida
James Default
 

not 300 psi but 30. Scale is 500 milli volts for whole screen and it is running 300mv.

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Gil Technician
Fresno, California
Gil Default
 

Try the second waveform same way but only cranking engine , make sure the throttle is closed, then cranking again and first look in exhaust

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Jeff Technician
West Columbia, South Carolina
Jeff Default
 

intake Valve definitely not opening in that in cylinder waveform

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Ray Diagnostician
North York, Ontario
Ray Default
 

This capture shows the 4 piston strokes and the cranking compression stroke measures 16 psi. The intake valve in not opening. The intake valve is not opening when the piston is moving down and both valves are closed. The sealed cylinder will create 26 inches of vacuum.

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Gil Technician
Fresno, California
Gil Default
 

You say that you were able to rotate the engine and see valves open , the in cylinder waveforms are from cranking compression and may not see intake valves movement, but that deep of an exhaust pocket on bad cylinder is probably due to a leak , cranking engine with ignition synced on bad cylinder and first look sensor in the intake, if intake valve Is leaking then Pressure will increase when…

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Jeff Technician
West Columbia, South Carolina
Jeff Default
 

You are right Gil, I missed that earlier, I just assumed it was a running compression waveform because that’s how I would have tested it, guess I need to read closer, thanks for pointing that out.

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Gil Technician
Fresno, California
Gil Default
 

👍

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Ray Diagnostician
North York, Ontario
Ray Default
   

James, do a cylinder leakage test, I think you'll find a leaking valve.

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James Owner/Technician
Jacksonville, Florida
James Default
 

Yes sir, one of the 2 exhaust valves dropped the seat. leaking by it. impact marks all over the top of the piston.

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Robert Diagnostician
Fair Oaks, California
Robert Default
 

On the bad cylinder the deep vacuum pocket when the piston comes down and the exhaust valve has not opened, is due to a leak of compression on compression stroke. When the piston is going up compressing, air is leaking past a valve or rings. When the piston is on the way down it reaches zero pressure before it reaches the bottom and creates vacuum in the cylinder. You can see the difference with…

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James Owner/Technician
Jacksonville, Florida
James Default
 

You were correct. exhaust valve leaking. badly

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