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Discussion Starter #1
Hi, i have recently purchased ex police charger 2012 dodge with hemi and it was run fine emmision pass all good and then i got missfire on cylinder 8 i changed plugs coils and one injector on cylinder 8. First i was getting one code for cylinder 8 now i got p0300 and p0308 randome misfire. Can anyone had same issue and how to resolve. Please help i run out of ideas.
 

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Does the engine run rough?
Are your misfire codes popping up after or during a spirited or wide open throttle session? Or just under normal driving?

How did the plugs look on Cylinder 8? Lets see a close up picture.
 

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Discussion Starter #3
Plugs are brand new installed last week i checked yesterday and its good also i did pressure test it is high 250 or 240 psi but consistent i gues because it was pursuit vehicle. Code come most of the time in idle i drove it 600 miles no issue sometimes on regular driving comes. I was idle today for few minutes and it comes these 2 codes for the 1st time together. I replace that one injector today idle for few minutes drove it around nothing. There is no rough idle I just feel small hick on the steering barely hard to feel but it feels its not stady if aomeone sits whos not familiar with mechanics it wont notice.
 

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Edit - stupid thought - ignore
Was wondering if it could be a faulty connector leading upto Cyl #8 coil pack
 

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Trouble is there are several possibilities. Anything from a bad wire or connector, or sensor, or bad lifter roller wearing down a cam lobe.

With the P0300 designating a random MF and you could have a bad Crankshaft position sensor. It reads off the reluctor wheel teeth and can get it wrong if things are not in good shape. I asked if they were @WOT because at upper RPM's they can be in error. Not often but it happens.

You can try replacing it. It requires moving the starter out of the way.

I had a P0308 @WOT that wound up being bad valve seals on Cylinder 2 oiling the plugs. Thats why I would pull ALL the plugs after misfires. Are you smoking a little when you fire it up?

Plugs don't have to be black to indicate misfires. If they foul and stop firing yes. But an occasional MF because of light oil is possible.

Here is a plug from my Cyl #2 that had bad valve stem seals. Note the insulator looks sugar coated and the ground strap doesn't look dry.

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If you wind up wanting to see if you have a bad lifter you can pull the valve cover(s) and bump the starter over and see if all the springs compress fully.
They should look almost fully compressed with very little space between the coiled wire.

I made up a bump starter from a momentary rocker switch plugged into the starter relay socket.
Remove the relay (and the fuel pump relay) insert the switch wires into the right and left slots (as viewed standing in front of the bumper).
Bump her over comparing the springs to each other to see if they all compress fully.

Good luck, Hopes its simple.

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Check your oil, is it all glittery? That's the tell tale sign of knowing it's the lifter roller eating into your cam.
 
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