Compression waveform

Darren Mechanic Wisconsin Posted   Latest  
Discussion
Driveability
2002 Chevrolet Malibu 3.1L (J LG8) 4-spd (4T40-E)

Compression waveform shows some type of problem at arrows, sorry about phone picture. Any ideas what problem could be? Dead misfire at idle only, no misfires above 2000 rpm. 

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Brandon Diagnostician
Pennsylvania
Brandon Default
 

this momentary lapse in pressure change is represented by the anomaly in the exhaust ramp. Look for fault that hinder the operation of the exhaust valve (like carbon/sticky guide/valve seat issues)

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Brin Diagnostician
Florida
Brin Default
   

Brandon's hindering the exhaust valve statement is good. My first thought would be a cam lobe or rocker arm roller issue.

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Brandon Diagnostician
Pennsylvania
Brandon Default
 

Brin, What you’re saying could be true as well. Mine was more of a blanket statement. Cam lobe/lifter issue can cause the same hinderance 👍

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Brin Diagnostician
Florida
Brin Default
 

Word! I agree with your statement. I was just taking a stab with the application in mind.

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Greg Technician
Colorado
Greg Default
 

Would like to see more repetitions of the exh. ramp... If repeats every time suspect cam lobe. If walks around, suspect roller.

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