P0300 Eng misfire after headers/heads
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P0300 Eng misfire after headers/heads
I put the dynatech header kit on my car at the same time I replaced the heads with stock LS6 heads and when I got it all back together I am getting a P0300 code on the DIC. I did unhook the air injection system but I don't think that would have anything to do with the code. Also it is running real rich, the high flow cat on the drivers side was glowing red but the pass side was fine. I called dynatech and they said it was glowing because it was burning excess fuel not burned by the engine. It runs smooth when you first start it up for about 2 min even with it revved up to 2k it holds steady, but after it warms up to approx. 100 deg Eng temp it will start to misfire and the idle fluctuates. At WOT it does not seem to misfire, but I can't say for sure. After it's warm if you give it a little throttle it will not rev but after a few seconds of holding the pedal steady it will jump up to the appropriate RPM based on the throttle position. I have triple checked every connection/hose and everything is hooked up. I don't know why it runs fine until it starts to warm up. I was thinking it may be a bad O2 sensor but I am not getting any codes other than the one.
#3
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The car runs in open loop until it warms up a bit. Check to see if you hooked up the O2 sensor wires in reverse. They cross each other in the normal rear set-up and you may have accidentally put the wrong one in the wrong pipe. It sounds to me that the car messes up the fueling when it goes into closed loop. It takes some time to allow the O2's to warm up first. Reversing these wires gives the symptoms of misfueling that you are reporting. Remove the O2's and put them in the opposite pipe.
Last edited by SpinMonster; 03-25-2006 at 09:51 PM.
#4
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Get a Tech II scan tool hooked up to do some diagnostics. A P0300 could conceivably be any one of several different things including, a plug, plug wire, coil, any of the electrical connections between the PCM and coils, open circuit in one of the coil wiring harnesses on the valve covers, etc. The Tech II can check the PCM's Failure Records etc to see what conditions existed at the time of the misfire. HTH
#5
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Originally Posted by LoneStarFRC
Get a Tech II scan tool hooked up to do some diagnostics. A P0300 could conceivably be any one of several different things including, a plug, plug wire, coil, any of the electrical connections between the PCM and coils, open circuit in one of the coil wiring harnesses on the valve covers, etc. The Tech II can check the PCM's Failure Records etc to see what conditions existed at the time of the misfire. HTH
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Originally Posted by silvervette02
I put the dynatech header kit on my car at the same time I replaced the heads with stock LS6 heads and when I got it all back together I am getting a P0300 code on the DIC. I did unhook the air injection system but I don't think that would have anything to do with the code. Also it is running real rich, the high flow cat on the drivers side was glowing red but the pass side was fine. I called dynatech and they said it was glowing because it was burning excess fuel not burned by the engine. It runs smooth when you first start it up for about 2 min even with it revved up to 2k it holds steady, but after it warms up to approx. 100 deg Eng temp it will start to misfire and the idle fluctuates. At WOT it does not seem to misfire, but I can't say for sure. After it's warm if you give it a little throttle it will not rev but after a few seconds of holding the pedal steady it will jump up to the appropriate RPM based on the throttle position. I have triple checked every connection/hose and everything is hooked up. I don't know why it runs fine until it starts to warm up. I was thinking it may be a bad O2 sensor but I am not getting any codes other than the one.
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Originally Posted by SpinMonster
All connections are fine if it runs fine for the first few seconds. It freaks when it goes into closed loop after warming. When you go to WOT it doesnt use the O2's and he says it is ok there.
Thanks a lot for all the input. The 02's are hooked up to the correct sides (crossing each other). What exactly do you mean when you say it goes into closed loop when it warms up?
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Originally Posted by vetred
Dude,......ME TOO! Guess what it was????/ When WE did the hedders we broke about six plugs! you couldnt even see the breaks! but when we replaced them everything was
Edit: I pulled the plugs on the passenger side and all 4 are black. The 4 on the drivers side all looked normal. Same goes for the fwd 02's. The #8 plug's gap was about twice what it should be, somehow it got bent putting it back in. I wonder if the #8 plug not getting a good spark with a wide gap could have caused all this. This would explain the miss and the #8 fouled plug and 02 sensor but why would the other 3 plugs on the right bank also be fouled? Could it be that #8 misfiring fouled the 02 sensor and in turn the 02 stopped reading the mixture correctly causing the other 3 plugs to foul? I am going to replace all the plugs tomorrow and hopefully that will solve my issues. Wish me luck.
Oh yea, should I go with stock plugs or a hotter plug.
-Chad-
Last edited by silvervette02; 03-26-2006 at 03:13 AM.
#9
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Originally Posted by silvervette02
Thanks a lot for all the input. The 02's are hooked up to the correct sides (crossing each other). What exactly do you mean when you say it goes into closed loop when it warms up?
I went through this with someone else on this board who insisted they were in correctly. I found out later that he swapped them after not finding anything else to try and his car ran fine. He never posted the solution publically. If yours are in correctly, one is bad but I doubt it. Humor me and invest the ten minutes for the swap.
If your car runs right for the start-up then your plugs, wires, and hardware are all fine. After warm-up the O2's are the variable here. A bad part wont ever run right unless its attached to the O2 circiut like an extension wire. So the coil and spark plug theory don't hold water. Hey, I've been wrong before.
EDIT: you cant mess up the front ones. The rear O2's are the reversed ones. The right wire feeds the left pipe.
Last edited by SpinMonster; 03-26-2006 at 10:03 AM.
#10
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CI 6,7,8,9,11 Vet
St. Jude Donor '08
Is the P0300 code the ONLY code that your getting?? Look for damaged O2 sensor wires. That seems like the only way one entire bank could be hosed! I still think you should see other codes if it running that bad. Could be a bad O2 sensor.
Bill
Bill
#11
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possibilities are: the front o2's are crossed[o2's in collectors are crossed.left should go to left/right to right]
cracked plugs
plug wires not on all the way or burnt
coil packs on the wrong side of motor.NOTE:BEFORE I'M FLAMED.the coils themselves are all the same,BUT the racks/harnesses are WIRED DIFFERENT.looking at the gray plugs that plug into the engine harnesses,on the left bank[drivers side]the coil plug with the control wires should have the following colored wires:coil pack for left bank-purple[1]-lt.blue[3]-dk.green[5]-red[7].engine harness plug for left bank has the same matching colors.
on the right side bank 2-the colors are different-coil pack colors are:
red[2]-dk green[4]-lt blue[6]-purple[8].the engine harness plug will be
red/white[2]-dk/green/white[4]-lt.blue/white[6]-purple/white[8].
if you cross the coil rails[left/right],1 side of the motor will misfire.
it's kind of hard to mixmatch the coil packs,but if done will drive you nuts.
p0300 means multiple misfires[pcm sees multiple cylinders misfiring]
cracked plugs
plug wires not on all the way or burnt
coil packs on the wrong side of motor.NOTE:BEFORE I'M FLAMED.the coils themselves are all the same,BUT the racks/harnesses are WIRED DIFFERENT.looking at the gray plugs that plug into the engine harnesses,on the left bank[drivers side]the coil plug with the control wires should have the following colored wires:coil pack for left bank-purple[1]-lt.blue[3]-dk.green[5]-red[7].engine harness plug for left bank has the same matching colors.
on the right side bank 2-the colors are different-coil pack colors are:
red[2]-dk green[4]-lt blue[6]-purple[8].the engine harness plug will be
red/white[2]-dk/green/white[4]-lt.blue/white[6]-purple/white[8].
if you cross the coil rails[left/right],1 side of the motor will misfire.
it's kind of hard to mixmatch the coil packs,but if done will drive you nuts.
p0300 means multiple misfires[pcm sees multiple cylinders misfiring]
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St. Jude Donor '11-'12-'13, '15
I am gonna say that I bet it has something to do with the O2 sensors. Either they are in the wrong positions, or a wire got pinched......When I did my LG header install, my car did the same thing and when I checked the plugs one side of the engine they were sooty black, other side were clean as when they came out of the box! Also I had the misfire code as well. Cause was O2 sensors on wrong sides! Swapped them and she ran like a top.
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After I drove it againg last night I drove it real easy and didn't get a check engine light but it was still missing the same. I got back and checked and it had two this time, both current. They were P0300 and P0174 (lean bank 1), no code for bank 2 but that is the side running rich. The switching of the 02's sounds like what I should do but when I climbed under the car to try that the wires aren't long enough. I did take them out and look at them. I'm going to scan it today and see if the 02's are working properly and I will try to find a way to switch them, but that would put the right 02 going to the right collector and the left to the left. Maybe it is a broke wire but wouldn't that throw a code for the 02.
This is probably important too. I forgot to mention that when I did get the check engine light it would flash. I read that it will flash when the cats are not working right or at least when the car doesn't think they are.
-Chad-
This is probably important too. I forgot to mention that when I did get the check engine light it would flash. I read that it will flash when the cats are not working right or at least when the car doesn't think they are.
-Chad-
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CI 6,7,8,9,11 Vet
St. Jude Donor '08
A flashing CHECK ENGINE light (CEL) is an indication of engine misfire. You may or may not see DTC P0300. On some cars, the DTC P0300 wont set until the PCM see's a certain number of misfires. The flashing CEL indicates that the mis fire is being detected now. The P0300 will not set on some car's just because the CEL is flashing and if you pull up the DTC's when the CEL is not flashing sometimes the code will NOT be set. If the DTC is set, the misfire condition was happing for large number of ignition cycles.
BC
BC
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Originally Posted by silvervette02
After I drove it againg last night I drove it real easy and didn't get a check engine light but it was still missing the same. I got back and checked and it had two this time, both current. They were P0300 and P0174 (lean bank 1), no code for bank 2 but that is the side running rich. The switching of the 02's sounds like what I should do but when I climbed under the car to try that the wires aren't long enough. I did take them out and look at them. I'm going to scan it today and see if the 02's are working properly and I will try to find a way to switch them, but that would put the right 02 going to the right collector and the left to the left. Maybe it is a broke wire but wouldn't that throw a code for the 02.
This is probably important too. I forgot to mention that when I did get the check engine light it would flash. I read that it will flash when the cats are not working right or at least when the car doesn't think they are.
-Chad-
This is probably important too. I forgot to mention that when I did get the check engine light it would flash. I read that it will flash when the cats are not working right or at least when the car doesn't think they are.
-Chad-
you could have a bad o2.if you have no air/vacuum leaks on bank 1,swap the front o2's side to side,if the fault goes over to bank 2 the o2 is bad
Last edited by dpd; 03-26-2006 at 12:09 PM.
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Well that clears it up. I went back and read the previous posts and, well, I'm an idiot. I kept reading it as: the right should cross over to the left and the left to the right so that is probably my problem. Stupid, stupid, stupid.
Thanks
Thanks
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Originally Posted by silvervette02
Well that clears it up. I went back and read the previous posts and, well, I'm an idiot. I kept reading it as: the right should cross over to the left and the left to the right so that is probably my problem. Stupid, stupid, stupid.
Thanks
Thanks
no-the fronts stay left to left,right to right.the REARS cross over,left to plug in right side and right over into left.if you have the FRONTS[o2's in the collectors]crossed[left plugging into right and vice versa],then yes,you have them crossed.
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Well after changing the front 02s to where the right goes to the right and the left to the left it runs like new, well except for the huge power increase. I think I am still going to change the plugs since I fouled the whole right bank. Thanks a lot for the help, You guys saved me a lot of headache . I had to cut all the zip ties and relocate the wires to keep them off the headers and still be long enough, this took about 45 mins . Now everything is great and I'm ready to put my cam in next weekend .
-Chad-
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St. Jude Donor '11-'12-'13, '15
Glad you got it cleared up! You probably don't need to change the plugs again as that soot (on mine anyway) was so fresh and soft I basically just wiped them clean ensuring the gap area was cleaned as well. Not a problem since.