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Discussion Starter #1
In my post a few days ago, I mentioned that I have a P0305 code and the engine (6.4) is actually missfiring in the #5 cylinder. I am bracing for the worst. A question regarding repair procedure if it is determined that the valve spring is broken, Is it always necessary to remove the head? Is it possible/acceptable to pressurize the cylinder with compressed air and replace just the broken spring? Anyone else ever experience this situation?
Thanks in advance..
 

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Never experienced it in cylinder 5 or on a 392. Yes you can pressurize the cylinder (if it will hold pressure) and get a compression tool to change the spring without removing the head. What else have you looked into it being because misfires can be any number of things? Any noise coming from the motor/valvetrain? If you broke a valve spring you *should* have dropped a valve and grenaded the motor. If you didnt I would say its something else. I would not start with the worst, I would start with the most simplistic. Pull your plugs (in that cylinder) and inspect them (are all your plugs up to spec?). If you are still concerned it is a broken spring, dont do the following but if you suspect something else then continue. Change coilpacks around and see if you still have the misfire on cylinder 5. Next pull the valve covers and inspect the springs, pushrods and rockers (do this one before swapping coils if you want to be safe). Did you clear the code and it came back? I have had a random misfire over the course of 4 years, cleared and dont come back for roughly a year or more (happened twice and no more since 2 years ago). Sometimes they just randomly happen depending on certain circumstances (fuel, mods, weather, maintenance).
 

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Discussion Starter #3
It is not yet diagnosed. I am just bracing for the worst. There is no doubt, the engine is running very rough (missfiring) consistently. I seem to think that the injector is functioning as you can smell un-burned fuel in the exhaust. You can also hear a nice crisp ticking when you listen to the injector. It sounds the same as the others. I will look into the coilpack next. Don't these have 2 spark plugs per cyl? How likely would you have both fail at the same time?
 

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Still running just rough? I would not say its a valve spring then. Could be but I would look elsewhere. When did it start? That will help diagnose. Yes 2 plugs per cylinder but if one goes out it will cause a misfire. Your engine maintenance up to date? Plugs are within life span? Only p0305? Not an injector then. Pull plugs then try the coilpacks (clearing the codes after the coilpacks to see if it returns).
 

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Discussion Starter #5
Just replaced the coilpack, problem still there. Running rough and missfiring. The engine only has 29,000 miles on it! No other codes, just the P0305. No unusual noises. When it happened it was just a couple miles from home. Made it home and parked it.
 

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Okay, you need to do things in a systematic order. Did you first pull the plugs of that cylinder? Try that first. Clear the code every time you do something. Did you clear the code after swapping coilpacks? You absolutely need to clear the codes or you will never be able to tell. The computer will still diagnose a misfire (even if there isn't one) if you don't clear the code. There's absolutely no noise in the engine I would say it's not a valve spring but it could be a very slight break issue. How were you driving the car on your way home, very aggressive or normal? Did you just get gas?
 

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Discussion Starter #7
It happened immediately after a downshift (M6) and a hard acceleration. RPMs maybe got to 5000-5500. Well under the 6400 redline. Going to pull the sparkplugs and see what they look like.
How do you clear the code?
 

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Okay valuable info... I would be more concerned now. I would no longer run the engine until you find the problem or lack of a problem. To clear codes you need a simple code reader (like $20-40 at walmart or any autoparts store) that plugs into the cars OBII port under the steering column just above the pedals. If you have a hand held tuner you can do it that way as well i believe. There will be an option within whatever device you use that will allow you to clear the codes on the car. How skilled are you mechanically? If you feel comfortable I would say you can figure this out mechanically but if you dont then I would strongly suggest taking it to the dealer or a shop. My recommended course of action for the somewhat skilled mechanic: CLEAR CODE FIRST, pull plugs and check, pull valve cover and inspect springs and rockers and pushrods (pulling the rocker assembly if needed), if no observable issue then replace valve cover and swap coilpacks now that the code has been cleared, start the engine and see if code returns. If it does not immediately come back, take a short drive and be very gentle on it.

Any mods done to the car at all? Being that it is an m6, I have never heard of a pushrod bending but I suppose you could be the first. That would cause a misfire. What model/trim and year of car please?
 

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Discussion Starter #9 (Edited)
Its a 2011 SRT8 6.4. Spark plugs looked fine. No engine mods ever. For some reason I still want to think it is electrical, because of the unbruned fuel smell. If the plugs were firing, there shouldn't be any fuel smell I would think.. I have no way of diagnosing it further electrically beyond replacing the coil which I just did. Could it be something in the ECU or crank position sensor that would prevent the #5 coilpack from firing the plugs? When running it up after each repair attempt, it was definitely misfiring, but when I revved it slightly it revved fine (meaning no noise, backfiring, or any other symptoms). All else seems fine other than the steady missfire.

Regardless of how this turns out... thank you so much for offering your guidance this afternoon!
 

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With the miles on the car I would highly doubt it is anything electrical however it could be. If it were the crank sensor, the car would not even start so its not that. It could still be an issue with the PCM/ECU and here is why.

The way misfire codes work on the computer, even if you correct the code mechanically, the code will still be present (CEL on) until you manually clear it or the car goes through 3 drive cycles (thus why I have been stressing to clear the code). The misfire may be gone but the computer still thinks its there and can actually still cause the car to feel rough as if there is a misfire. So even though you swapped the coils and it didnt solve it, you may actually have and the computer will still be showing the code. It also may just be a random misfire like in my circumstance. The only way to know is by clearing the code. You gotta clear the codes. I would still pull the valve cover and check the springs and rockers and pushrods given the circumstance you received the code in, just to be safe.

No problem on the help. Let me know anything further or if you get it figured out! Feel free to PM me if you need more help.
 

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Discussion Starter #11
Wow... I am surprised to learn that even if the problem may be fixed, if the code isn't cleared the problem will still exist! Thats crazy. Can I clear the code by removing the fuse for the PCM for a few minutes... or disconnect the positive battery cable for a few minutes?
 

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Disconnecting the battery for 5 minutes should work. After you reconnect it, turn the key (or just push the button without foot on brake) to turn the car to on but not running the engine. Watch the check engine light if it flashes then stays on there are no codes, If it never flashes and/or you hear a chime, there is a code still. The newer cars sometimes wont clear codes entirely by disconnecting the battery but they should clear the actual check engine light.
 

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Discussion Starter #13
Got the CEL extinguished, problem still the same though. I think I'm about done with it. I could take off the valve cover but whats the use? if anything is broken, I'm not fixing it. Probably best to take it to the shop. Got one about a mile away. I will be sure and report back as to what was found. Probably won't be till early next week though.
 

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Sorry about it. Good luck with it and yes please do let me know what it was in the end, always interested. Best of luck!
 

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could be a failed lifter as well. I would pull the valve cover off and do a visual inspection for the spring. If all good then possible lifter. you could also do a leak down and compression check on that cylinder that will tell the true story.
 

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Discussion Starter #16
If it is a lifter, could that be replaced by just removing the intake and the appropriate rocker arm, leaving the cyl head in place?
 

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Negative. To replace lifters the cylinder head has to be removed. Wish they didn't have to be.
 

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Discussion Starter #18
Update. So, as it turns out, there was an actual valve failure in the #5 cylinder. I was very surprised and disappointed to hear this as the car has less than 30,000 miles on it and is very well maintained by a local Dodge dealership. No modifications whatsoever. Total repair cost was just over $2,000.00!!

I did contact Dodge customer service and that was an EPIC FAILURE as well.
 

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Interesting... like hearing stories finish out. Still under warranty then or did you have to catch that bill? Glad you got it all fixed though!
 

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Discussion Starter #20
Out of warranty. It is an '11 SRT8. That's why I initially reached out to Dodge Customer Service. In my mind, there was clearly a flaw somewhere as these engines don't normally have these kinds of failures at less than 30,000 miles. Again, it was very well maintained by the dealer and never modified. As I mentioned previously, my experience with Dodge Customer Service was a complete and total failure. They absolutely suck. My car sat at the dealership for over a month waiting for Dodge Customer Service to coordinate with the dealership. It never happened. So I just worked it out with the Dealer.
In the end, the local dealership (without any support from Dodge Customer Service) offered me an opportunity to purchase an extended warranty, then the repair would be covered under that warranty. That was the final outcome.
 
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