New to me, need some help. Bought it from a lady who's kid was apparently driving it hard when this started. Issues are as follows:
P0300, misfiring mostly on 1&4, some on 2, occasional random
bad belt tensioner (on order)
platinum plugs (replaced with copper)
KN air filter, after market intake (planning to go back to stock for simplicity)
leaking oil from valve cover into plug wells
broke the line from the throttle body to the purge can while changing plugs, will patch.

So I replaced the plugs, all 16, they were extremely black and cruddy and all over gapped. One even had a slightly bent electrode. Now it idles, but still misses pretty bad. If I rev it to 3000, it smokes dark smoke. Oil looks OK, antifreeze is a touch low. I swapped a known good coil from 3 to 1, no change. I intend to do the same swap with the injector. The PCV valve rattles when I shake it. Planning to do a compression test when I can get it in the shop since the weather just went bad here today. I've suspected everything from the EGR to a busted valve spring to bad fuel and at this point I'm just going in logic circles from part to part. I'm betting on more than one issue, which makes it difficult to diagnose when I'm new to these engines. Where would you start? TIA.

 

Compression test before any more new parts

 

Will do. Thanks.

 

A cylinder leakdown test would be a good idea too.Good luck.

 

If you haven't already, you might check the throttle body/plate for blow by build up. New plugs didn't cut the highway MPG I lost over several years when first bought. I was down to 13 from 18. I cleaned mine (without removing) with a Seafoam soaked rag. It got the MPG back. Doing it every couple years since.

 

Got my gauges and adapters today, will test when I can get under the hood again. Got chilly here and work keeps getting in the way of the fun stuff.

 

Keep us updated. Curious to see what you find. These Hemi's are usually bullet proof. My 08 is at 103K and has been tuned for 93 octane since almost new. Been flawless so far.. The lifetime powertrain warranty has been great, but haven't had to use it yet. Hopefully it's nothing too serious!!

 

1 & 4 (my 2 misfires) making 0 PSI even wet. I hope to do a leakdown on it tomorrow and check compression on the other 6 cylinders as well. Looked at the top of the #1 piston with a camera, don't see a hole. Seems like maybe a valve, but I guess the leakdown will tell me for sure.

 

Daves69,
Since you mentioned it, I checked this out. There is quite a bit of build up on the plate/ in the throat. I'll clean it if I can get the other issues solved.


Finally did a leakdown on #1, air noise at the oil cap and the exhaust tip. I turned the cylinder to TDC again in case I was on the exhaust stroke, still noise at the exhaust pipe. Can see some odd lines on the top of the piston with the camera, I'm a little afraid I lost a valve seat. Haven't really looked at the #4 yet, its my other serious miss. Would you guys just pull the heads and figure it out when you get there? I'm starting to look at rebuilt engines, but would rather repair this if it is financially viable.

 

Your original post stated you had a damaged plug...did that happen to come from 1 or 4?
I think if it were mine I would pull valve covers and rocker arm shafts. This would ensure valves are closed. Then leak down test on 1 and 4. If bad result your already on your way to removing heads. Get heads off and try to make a decision on rebuilt heads or reman engine....kinda sounds like reman engine or good used is where your heading..but at least you can confirm and be at peace with your decision??? just an idea. Only downfall to this is heads are easier to remove when engine out.