Help, Random, Multiple Misfires after New Plugs
Thread Starter
Racer
Joined: Jul 2004
Posts: 279
Likes: 0
Help, Random, Multiple Misfires after New Plugs
Hey Guys,
I just installed new plugs on my 25k mile 2004 Z06. I used NGK Tr55's. The install was pretty easy and all was well until i decided to test drive the car.
When in idle car revs smootly and does not misfire.
When under load around 4k rpm it misfires bad and throws the P0300 code multiple misfires..
Whats wrong
I appraciate your help
Ken
I just installed new plugs on my 25k mile 2004 Z06. I used NGK Tr55's. The install was pretty easy and all was well until i decided to test drive the car.
When in idle car revs smootly and does not misfire.
When under load around 4k rpm it misfires bad and throws the P0300 code multiple misfires..
Whats wrong
I appraciate your help
Ken
Le Mans Master
Joined: Nov 2000
Posts: 6,266
Likes: 156
From: Galloway Twp. NJ
Cruise-In VII Veteran
well........ it HAS to be something related to the new spark plug install.
check your spark plug wire connections.
make sure all plug wires are securely pluged into the spark plugs (push until they "click" into the plug).
make sure you didn't damage a plug wire while you were unpluging them.
check your spark plug wire connections.
make sure all plug wires are securely pluged into the spark plugs (push until they "click" into the plug).
make sure you didn't damage a plug wire while you were unpluging them.
Team Owner
Joined: Oct 2001
Posts: 46,766
Likes: 5
From: Boynton Beach Florida
St. Jude Donor '07-'12, '20
All you did was replace the plugs? Nothing else? As posted above make sure the wires are plugged into the plugs. Then, if that's the case you may have broken a wire when removing them from the old plugs. I would check the wires first and then check for a broken (cracked) plug.
Thread Starter
Racer
Joined: Jul 2004
Posts: 279
Likes: 0
When tightening the rear driver side (the hardest plug) it made a "cracking" sound when i was tightening it....
maybe this is the case.
But wouldn;t a cracked plug make the engine run bad...when in N the car revs nicely...only under load does it misfire.
maybe this is the case.
But wouldn;t a cracked plug make the engine run bad...when in N the car revs nicely...only under load does it misfire.
Safety Car
Joined: May 2000
Posts: 4,827
Likes: 352
From: Albuquerque NM
As above said, check wires. But, what did you gap them to?
Maybe too much gap.
Looks like you posted the probable problem just as I posted. Check that plug. If it's damaged it'll act up under load.
Maybe too much gap.
Looks like you posted the probable problem just as I posted. Check that plug. If it's damaged it'll act up under load.
Team Owner
Joined: Oct 2001
Posts: 46,766
Likes: 5
From: Boynton Beach Florida
St. Jude Donor '07-'12, '20
Originally Posted by CAPTKEN28
When tightening the rear driver side (the hardest plug) it made a "cracking" sound when i was tightening it....
maybe this is the case.
But wouldn;t a cracked plug make the engine run bad...when in N the car revs nicely...only under load does it misfire.
maybe this is the case.
But wouldn;t a cracked plug make the engine run bad...when in N the car revs nicely...only under load does it misfire.
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Thread Starter
Racer
Joined: Jul 2004
Posts: 279
Likes: 0
Ok i rechecked to make sure all wires were on tight. and took it out on a lil spin...For the first 10 min of hard driving i experianced no misfires. But once the engine was warmed up 192* i only experianced misfires under WOT and past 5k rpm. So it might be the last plug. And i will check it once the car has cooled down enough (its 50 deg so it will be about 30 min.) If it is cracked i will go get another one and follow up...
Thanks guys...You Rock
Thanks guys...You Rock
Intermediate
Joined: Nov 2005
Posts: 45
Likes: 0
Yeah sounds like a bad plug of some sort. If you heard one crack as you tightened it down, that would be the first one I would check.
Also did you use a torque wrench or anything to tighten them with, or just tighten them down hard? (I'd go find a tq wrench and find out what they should be torque'd too personally) I would also pull them and make sure they are gapped correctly (usually they are, but occasionally I've found some that aren't).
Good luck.
(PS. why are you changing them after only 25k miles, shouldn't they be good for alot longer?)
Also did you use a torque wrench or anything to tighten them with, or just tighten them down hard? (I'd go find a tq wrench and find out what they should be torque'd too personally) I would also pull them and make sure they are gapped correctly (usually they are, but occasionally I've found some that aren't).
Good luck.
(PS. why are you changing them after only 25k miles, shouldn't they be good for alot longer?)
Thread Starter
Racer
Joined: Jul 2004
Posts: 279
Likes: 0
I will be pulling the drive side rear one in about 15 min.....I will be replacing it with a new one just to be sure.
I cant fit a torque wrench in the small confines so i just tighten them until they are snug..
I will have the autoparts store check the gap on the new plug i buy....
I'll be back in 30 min
I cant fit a torque wrench in the small confines so i just tighten them until they are snug..
I will have the autoparts store check the gap on the new plug i buy....
I'll be back in 30 min
Drifting
Joined: Oct 2003
Posts: 1,540
Likes: 0
From: bloomfield nj
cracking noise during install? willing to bet the plug is cracked.other possibilities.did you feel the plug wires"click" when you plugged them back on?are you sure the heat sheilds didn't cut in to the plug boots? more than likely your c"cracking noise"plug is arcing to the heat sheild under load.
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 180
From: S.W. Ohio. . . . . . NRA Life Member
Originally Posted by CAPTKEN28
I did not check the gaps...They state they are gap'd to specs from the factory...;
Hummmm
Hummmm
My Delco Iridiums claimed that as well. 7 of them were perfect, one was w-a-y- off.
Le Mans Master
Joined: Dec 2000
Posts: 7,096
Likes: 153
From: "Atlanta" Ga.
Originally Posted by Mike Mercury
My Delco Iridiums claimed that as well. 7 of them were perfect, one was w-a-y- off.
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 180
From: S.W. Ohio. . . . . . NRA Life Member
Originally Posted by Gonzo
interesting, I wonder if all the ones used in maunfacture are gapped correctly, 1 in 8 is not good, with that ratio we all may have one poorly gapped plug....
the incorrect plug was gapped too narrow. I believe it was jolted pretty good in shipment/handling and was slammed onto the electrode.
Thread Starter
Racer
Joined: Jul 2004
Posts: 279
Likes: 0
Update:
I went and got another plug, waited until the engine was cool to touch before tackling the driver side rear plug. As i thought and with your helpful comments i took the plug wire off and heard some particles hit the ground and as i took out the plug the ceramic was cracked badly. Put new plug in and it was time to test drive...
I will post pics of my old (origional plugs) and the one that was cracked later but the problem is solved!
I even got to play with a S55 AMG and pulled nicely on him. But let me tell you those sure get out of the hole quick...
THANK YOU THANK YOU THANK YOU
Beers for everyone! 
I went and got another plug, waited until the engine was cool to touch before tackling the driver side rear plug. As i thought and with your helpful comments i took the plug wire off and heard some particles hit the ground and as i took out the plug the ceramic was cracked badly. Put new plug in and it was time to test drive...
I will post pics of my old (origional plugs) and the one that was cracked later but the problem is solved!
I even got to play with a S55 AMG and pulled nicely on him. But let me tell you those sure get out of the hole quick...
THANK YOU THANK YOU THANK YOU
Beers for everyone!
