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I just bought this cherry 2009 SRT8 and a couple days after bringing it home I get a check engine light, rough idle, etc. Pull the code and its a Multi Cylinder misfire. Dealership won't touch the car because it's "modified" but sold me a 100,000 warrantee..?. . . After letting them scratch their heads for a week, I just went and got the car and started turning wrenches myself. Pulled the spark plugs and low and behold I have a number of fouled plugs. Several were gapped correctly and the remainder were FAR out of tolerance. some of the plugs were bent to the point there was NO GAP AT ALL.:surprise: See pictures. I included a shot of the new spark plugs for reference.


I replaced all the plugs which was not cheap ($200). Pulled out the diablo predator tuner the previous owner was nice enough to leave with the car. Cleared the trouble codes and drove it for a bit. No new issues but I have never seen an engine do that. Anyone have any ideas? I am not feeling confident right now.
 

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Top of the piston is probably damaged due to contact with the spark plug. Only thing I know of that can cause that, valve open when it's not supposed to be.
 

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Did you note which cylinder(s) had the plug gap problem? I would pull the new ones and check the gap to confirm if the piston is making contact with them again. If not, check in a few days or a week after some miles are accumulated.
 

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If there was a mechanical issue the new plugs would be damaged immediately. Were they the correct plugs?
 

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My thoughts exactly. Do you think the heads are missing some washers or spacers which would allow the spark plug to sink deeper into the combustion chamber where they would make contact with the piston. I just hope the pistons aren't damaged.
 

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Top of the piston is probably damaged due to contact with the spark plug. Only thing I know of that can cause that, valve open when it's not supposed to be.


My uncle who is a pilot and old school hot rod mechanic, suggested I borrow a bore scope and take a look in the combustion chamber through the spark plug holes and inspect both the head and the top of the piston. Try and get an idea what is going on in there. I'll pull the coil pack and pull the two spark lugs from the worst cylinder and see what the plugs look like. I'll update the thread and see what we have. Thanks for your reply. I really appreciate it.
 

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Detonation will close the spark gap.
I doubt the engine is hurt otherwise the new plugs would have had their gaps closed as well once you ran it.
You said the car had a tuner, was it just a canned tune or was it a custom one?
If it was a custom one the tuner may have dialed in too much spark advance.
If it was a canned Diablo tune then it's possible the original owner dialed in more timing as well.
Either of those circumstances can cause detonation.
Are you running premium fuel? Did you bounce off the rev limiter or hear any detonation?
 

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Discussion Starter #9
Detonation will close the spark gap.
I doubt the engine is hurt otherwise the new plugs would have had their gaps closed as well once you ran it.
You said the car had a tuner, was it just a canned tune or was it a custom one?
If it was a custom one the tuner may have dialed in too much spark advance.
If it was a canned Diablo tune then it's possible the original owner dialed in more timing as well.
Either of those circumstances can cause detonation.
Are you running premium fuel? Did you bounce off the rev limiter or hear any detonation?


First of all thanks for your reply, you are very insightful and obviously knowledgeable about this.


I spoke with the previous owner over the weekend a couple of times and here is what I learned:
1. The tune on the car was custom built by a local shop in concert with a dyno, and it took into account the full cat delete exhaust and disabled the sensor errors that you would get from lack of those O2 (emissions) sensors.
2. It is possible that the tune in it had a little too much advance.
3. The salesmen at the dealership had no idea what they had. The guy that took the car in on trade didn't bother to pass along any pertinent information to the other salesmen, who showed the car to me. I know that the salesman that showed me the car had no idea it was tuned (although you'd think it would be intuitive).
4. Also I am positive they filled the car with regular 87 octane as they had it for a month and were test driving the vehicles with customers before I got to it.
5. It is possible that some donkey went to test drive the car and didn't hit a shift point, or over-revved the engine and probably bounced the car off the rev limiter. Which as you explained in your post is a possible reason for the closed or bent spark plugs.


As I said above the first step in trouble shooting this multi-cylinder misfire was to pull the spark plugs and get an idea of what was going on in the combustion chamber. I found the problem (obviously) no gap=no spark, thus misfire. Since I replaced the plugs I have had no new trouble codes. I will pull the coil packs and inspect the plugs this weekend after a full week of driving to see what I have but I think everything is fine, given how the engine is running now.


I said all that not because I want to insult your intelligence but rather for this reason: I feel this is all good information that someone else with the same problem may find in the future and need for reference. For that reason can you explain how advanced timing and over revving the vehicle can cause detonation? I am pretty sure I will learn something new too.


Thanks again for your insight,


Rob
 

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Basically too much timing ignites the fuel/air mixture too soon so the remaining fuel spontaneously ignites after initial combustion (detonation). This causes a major short term pressure spike in the cylinder that can cause damage if left unresolved. Bent spark plugs are an indicator of long term detonation. Broken ring lands are a possibility in extreme cases.

Hitting the rev limiter has nothing to do with detonation. It is s safeguard and won't hurt anything. I hit it many times at the track with no damage. It's the guys who raise the limiter that have problems. I've always left it alone.
 

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Basically too much timing ignites the fuel/air mixture too soon so the remaining fuel spontaneously ignites after initial combustion (detonation). This causes a major short term pressure spike in cylinder pressure that can cause damage if left unresolved. Bent spark plugs are an indicator of detonation. Broken ring lands are a possibility in extreme cases. Hitting the rev limiter has nothing to do with detonation. It is s safeguard and won't hurt anything.
Unless, of course, the engine is running nitrous and the nitrous is being injected when you hit the limiter. Since the limiter on a challenger is a fuel cut off, it can lean the engine out and cause lots of issues.
 

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Unless, of course, the engine is running nitrous and the nitrous is being injected when you hit the limiter. Since the limiter on a challenger is a fuel cut off, it can lean the engine out and cause lots of issues.
Yes nitrous is the exception. I was speaking of non-nitrous applications, which I think OP has.
 

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Basically too much timing ignites the fuel/air mixture too soon so the remaining fuel spontaneously ignites after initial combustion (detonation). This causes a major short term pressure spike in the cylinder that can cause damage if left unresolved. Bent spark plugs are an indicator of long term detonation. Broken ring lands are a possibility in extreme cases.

Hitting the rev limiter has nothing to do with detonation. It is s safeguard and won't hurt anything. I hit it many times at the track with no damage. It's the guys who raise the limiter that have problems. I've always left it alone.

USMC341 pretty much summed it up except: when our cars hit the rev limiter they pull fuel.
Pulling fuel can cause the motor to run lean which can also lead to detonation.

Sounds like the tune was too hot on the timing and the car detonated from too low an octane or too much timing.
You've got a couple of options going forward: reinstall the tune and hope it's o.k. as is.
Reinstall the tune but modify it to take out a couple of degrees in timing at WOT.
Get a tune from someone else.
Let us know how you make out.
 

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So, you are going to get the money back for the 100K warranty they now won't honor, right? THAT is what I would really upset about. And the car.
 
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So, you are going to get the money back for the 100K warranty they now won't honor, right? THAT is what I would really upset about. And the car.
Hell yeah! I'm wondering the same thing!

I'd do a lot of data logging too, see what kind of KR you have. You may want to get Johan (Diablotoona) to go over the tune, in case pulling time only at WOT isn't enough.
 

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I have a 2008 challenger SRT8 that i just put a procharger on,along with some new colder spark plugs that I gaped at 35. But the prob i'm having is at high RPM's i get Multi Cylinder misfire witch could mean that i need better coils but would like to know if there is anything else that i could check 1st incase i don't need to spend the 300+ $ on good coils
 

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I just bought this cherry 2009 SRT8 and a couple days after bringing it home I get a check engine light, rough idle, etc. Pull the code and its a Multi Cylinder misfire. Dealership won't touch the car because it's "modified" but sold me a 100,000 warrantee..?. . . After letting them scratch their heads for a week, I just went and got the car and started turning wrenches myself. Pulled the spark plugs and low and behold I have a number of fouled plugs. Several were gapped correctly and the remainder were FAR out of tolerance. some of the plugs were bent to the point there was NO GAP AT ALL.:surprise: See pictures. I included a shot of the new spark plugs for reference.


I replaced all the plugs which was not cheap ($200). Pulled out the diablo predator tuner the previous owner was nice enough to leave with the car. Cleared the trouble codes and drove it for a bit. No new issues but I have never seen an engine do that. Anyone have any ideas? I am not feeling confident right now.
I am experiencing the exact same issue with my 07 Ford Sport Trac.My spark plugs are being damaged every few months.I am going to have an expert find out what the underline problem is.As soon as I know,I will update.
 

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Was there 2 damaged plugs in any 1 cylinder. I would not bet against someone installing the plugs that way. There are people out there that have no clue, and either dropped or banged them on the head trying to install them and closed the gaps up. I'd check new plugs early, then after a month, if OK, I wouldn't worry about it. If not, borescope.
 

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Reading this thread helped. My RT has experienced the same issues in the #1 cylinder. At 125000 miles I’m expecting the timing chain and tensioner to have some extra play in it.

I’ll be replacing the plugs and scoping the cylinder heads, in my profession I’m an aircraft engine mechanic and this seems to follow along those lines.

thanks for the thread I’ll keep you posted.
Rob
 
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