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compression test

eznaz

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I have been chasing a #6 misfire for a while now. it is not plug, coil or injector. could not find vacuum leak. replaced rocker arms on left bank although old ones had no slop. question is ; can i do a compression test with the upper intake off the car? or should Iskip it and go straight to a leak down to look for a valve problem?
 

Cbty2050

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Compression test can be done with intake off. I do compression 1st. Did you replace the lash adjusters?
 

Snekpete

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I had a similar issue with my 2016 Mustang GT. It turned out to be a malfunctioning CMVC actuator. These are butterfly valves inside the intake manifold that restrict air flow at mid to low throttle settings. Without them the motor will run rough at partial throttle causing a misfire code.

The 5.7 liter Hemi intake has a short runner valve that I believe performs the same function. As long as the intake is off I would check to see that this valve and actuator are working properly.
 

eznaz

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Compression test can be done with intake off. I do compression 1st. Did you replace the lash adjusters?
Thanks, I am going to recheck for vacuum leak tomorrow. I did replace injectors but am going to verify voltages. I suspect I will be tearing into the head again although I don't hear any ticking.
 

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