HELP: I have a misfire!
Thread Starter
Burning Brakes
Joined: Jul 2003
Posts: 811
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From: Nashville TN
HELP: I have a misfire!
My car is showing a P0300HC code wich I believe indicates a misfire. I have replaced the plugs as it was about that time anyway and checked the wires before putting them back on. The code remains and the car runs rough...any suggestions?
Drifting
Joined: Oct 2003
Posts: 1,540
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From: bloomfield nj
P0300 means all cylinders are missing randomly,if it is 1 cylinder,you will get a fault for that cylinder[po301,302,etc.].misfires are figured out by the crank and cam sensors[misfires are set when the crank speed slows down].i would look for vacuum/air leaks,loose plug wires,make sure the grounds on the back of the cylinder heads are clean/tight.if all checks out ok,i've seen some cam gear bolts come loose and the camshaft walking back and forth [cam sensor signal not jiving with the crank signal]creating the 300 fault.you replaced the plugs so i will assume the plug wires are on tight.other possibilities are corroded knock sensor harness[usually the rear,but also usually sets a fault].corroded wiring under battery box[from leaking battery],internal engine[broken valve spring[s],bent push rod[s]].just my .02
Le Mans Master
Joined: Jul 2002
Posts: 7,370
Likes: 8
From: Slave to the evil empire
Cruise-In V Veteran
St. Jude Donor '04
Originally Posted by dpd
P0300 means all cylinders are missing randomly,if it is 1 cylinder,you will get a fault for that cylinder[po301,302,etc.].misfires are figured out by the crank and cam sensors[misfires are set when the crank speed slows down].i would look for vacuum/air leaks,loose plug wires,make sure the grounds on the back of the cylinder heads are clean/tight.if all checks out ok,i've seen some cam gear bolts come loose and the camshaft walking back and forth [cam sensor signal not jiving with the crank signal]creating the 300 fault.you replaced the plugs so i will assume the plug wires are on tight.other possibilities are corroded knock sensor harness[usually the rear,but also usually sets a fault].corroded wiring under battery box[from leaking battery],internal engine[broken valve spring[s],bent push rod[s]].just my .02
If you don't have a scanner or if the scanner shows multiple/random misifire then you need to check your valve springs, the first thing I'd look at are the plug wires to make absolutely sure they are good.
Burning Brakes
Joined: Sep 2003
Posts: 875
Likes: 0
From: Louisville KY
My friend had the same problem... it took 5-10 min after cold start for it to start happening. Didn't have a problem with it initially but the heat probably got to the plug wires and they broke down. He got some HIGH temp plug wires (1600*F i think), 2000*F plug wire sheilds, and I think ceramic plug boots. Problem fixed. He can run the dog sh*t out of it now and no problem. The extra heat from the headers caused his problem. A random miss coupled with the headers... hmmm i would bet money that you have the same problem he did and its an "easy" fix. Good luck with it. 
Last edited by kpforce1; Oct 22, 2005 at 06:06 PM.
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Racer
Joined: Apr 2005
Posts: 466
Likes: 0
From: Greenville NC
My car is doing the same thing- it started after I took it to the drag strip for the first time. I replaced the igntion wires (after seing one had touched my LT headers), which seemed to fix it, but it started doing it again today after driving for 50 miles or so! Dont know what the deal is!
Randy
Randy
Advanced
Joined: Jun 2000
Posts: 50
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From: Paducah KY
MY '02 Conv. has started missing after a Z06 cam valve springs,push rods ,headers,cats,Xpipe change&tunning. the car dyno @303HP after changes Dyno @363HP after driving home from Dyno the car started idealing ruff and popping under exceleration. Going to the shop again tomorrow Mechanic over the phone thanks it a tunning computer problem getting PO200 injector control circuit code also front oxygen sensorsP1133/P1153
Pro
Joined: Aug 2005
Posts: 586
Likes: 0
From: Destin Florida
Originally Posted by kpforce1
My friend had the same problem... it took 5-10 min after cold start for it to start happening. Didn't have a problem with it initially but the heat probably got to the plug wires and they broke down. He got some HIGH temp plug wires (1600*F i think), 2000*F plug wire sheilds, and I think ceramic plug boots. Problem fixed. He can run the dog sh*t out of it now and no problem. The extra heat from the headers caused his problem. A random miss coupled with the headers... hmmm i would bet money that you have the same problem he did and its an "easy" fix. Good luck with it.
where did he get his wires and covers?
