Random multiple cylinder misfires... hmmm
03-22-2006, 09:33 AM
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Random multiple cylinder misfires... hmmm I'm in a world of hurt here 
Here's the summary of what happened:
Purchased my 2000 Z-28 with 29K miles on it. It already had a P-1SC installed. First problem I had with the car was overheating. I overheated the car BADLY. I got the issue fixed up and I was on my way. Didn't have any other problems until the first time I was at the track this year (maybe 5 months after overheating).... I ran the hell out of the car. Then when I was sitting in the staging lane, my SES light started flashing. I didn't feel or hear misfires however.
Diagnostic tool said P0303 misfire.
I replaced the plug. The problem went away for a few days, then the code came back. Then the light turned off after a few days. Then it came back on. I read the code again and got a random multiple cylinder misfire code.
I pulled the #3 plug today. It was midnight black. I had only been running the car for less than two weeks. The only other symptom I can see is that after running, there will be just a bit of smoke that comes out of the exhaust. Kind of grey-ish smoke. And there's not a lot of it, and it only seems to come out when I'm idling.
What are my possible problems here? Could it be something as simple as the spark plugs (which haven't been changed in a long time) or wires or coil packs? Or is it something a tad more serious, like a head gasket (from overheating and then running really hard sometime later) or a warped head?
Any suggestions would be terrific.
BTW, the car had been run very hard after the overheating last year, and there were zero problems.
--------edit:----------
I checked the oil. The color is normal but it's very low. I replaced the 3rd spark plug (for the 2nd time) and I noticed that there was OIL on the bottom of the wire going to the plug.
Furthermore, the smoke is white, without question. It seems to smoke constantly through the powerband, but it's less noticable at higher RPMs.
Lastly, the smoke has a very sweet smell to it.
Any ideas?
Here's the summary of what happened:
Purchased my 2000 Z-28 with 29K miles on it. It already had a P-1SC installed. First problem I had with the car was overheating. I overheated the car BADLY. I got the issue fixed up and I was on my way. Didn't have any other problems until the first time I was at the track this year (maybe 5 months after overheating).... I ran the hell out of the car. Then when I was sitting in the staging lane, my SES light started flashing. I didn't feel or hear misfires however.
Diagnostic tool said P0303 misfire.
I replaced the plug. The problem went away for a few days, then the code came back. Then the light turned off after a few days. Then it came back on. I read the code again and got a random multiple cylinder misfire code.
I pulled the #3 plug today. It was midnight black. I had only been running the car for less than two weeks. The only other symptom I can see is that after running, there will be just a bit of smoke that comes out of the exhaust. Kind of grey-ish smoke. And there's not a lot of it, and it only seems to come out when I'm idling.
What are my possible problems here? Could it be something as simple as the spark plugs (which haven't been changed in a long time) or wires or coil packs? Or is it something a tad more serious, like a head gasket (from overheating and then running really hard sometime later) or a warped head?
Any suggestions would be terrific.
BTW, the car had been run very hard after the overheating last year, and there were zero problems.
--------edit:----------
I checked the oil. The color is normal but it's very low. I replaced the 3rd spark plug (for the 2nd time) and I noticed that there was OIL on the bottom of the wire going to the plug.
Furthermore, the smoke is white, without question. It seems to smoke constantly through the powerband, but it's less noticable at higher RPMs.
Lastly, the smoke has a very sweet smell to it.
Any ideas?
Last edited by maxf; 03-22-2006 at 10:48 AM.
03-22-2006, 09:59 AM
#2
I'm having the same PO300 / PO307 code in my LT1, get the service manual from your library, it tells you to check all sorts of things, injectors, plugs/wires, MAF, maybe EGR? there's like 20 steps.. Just curious, when you checked your codes, was your engine on? On my car, if the engine is on and I read the codes I get PO307, if the engine is off (key is in on position) I get PO300.
03-22-2006, 10:46 AM
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Originally Posted by savethelinoleum
I'm having the same PO300 / PO307 code in my LT1, get the service manual from your library, it tells you to check all sorts of things, injectors, plugs/wires, MAF, maybe EGR? there's like 20 steps.. Just curious, when you checked your codes, was your engine on? On my car, if the engine is on and I read the codes I get PO307, if the engine is off (key is in on position) I get PO300.
03-22-2006, 01:40 PM
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you check the other plugs on that bank? you are FI so PCV may be gumming up the works more than usual. I would check all the plugs, see if it is cylinder, bank or all plugs affected. I know its a pain but...
03-22-2006, 10:22 PM
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Originally Posted by savethelinoleum
I'm having the same PO300 / PO307 code in my LT1, get the service manual from your library, it tells you to check all sorts of things, injectors, plugs/wires, MAF, maybe EGR? there's like 20 steps.. Just curious, when you checked your codes, was your engine on? On my car, if the engine is on and I read the codes I get PO307, if the engine is off (key is in on position) I get PO300.
03-22-2006, 10:25 PM
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Originally Posted by maxf
I'm in a world of hurt here
Here's the summary of what happened:
Purchased my 2000 Z-28 with 29K miles on it. It already had a P-1SC installed. First problem I had with the car was overheating. I overheated the car BADLY. I got the issue fixed up and I was on my way. Didn't have any other problems until the first time I was at the track this year (maybe 5 months after overheating).... I ran the hell out of the car. Then when I was sitting in the staging lane, my SES light started flashing. I didn't feel or hear misfires however.
Diagnostic tool said P0303 misfire.
I replaced the plug. The problem went away for a few days, then the code came back. Then the light turned off after a few days. Then it came back on. I read the code again and got a random multiple cylinder misfire code.
I pulled the #3 plug today. It was midnight black. I had only been running the car for less than two weeks. The only other symptom I can see is that after running, there will be just a bit of smoke that comes out of the exhaust. Kind of grey-ish smoke. And there's not a lot of it, and it only seems to come out when I'm idling.
What are my possible problems here? Could it be something as simple as the spark plugs (which haven't been changed in a long time) or wires or coil packs? Or is it something a tad more serious, like a head gasket (from overheating and then running really hard sometime later) or a warped head?
Any suggestions would be terrific.
BTW, the car had been run very hard after the overheating last year, and there were zero problems.
--------edit:----------
I checked the oil. The color is normal but it's very low. I replaced the 3rd spark plug (for the 2nd time) and I noticed that there was OIL on the bottom of the wire going to the plug.
Furthermore, the smoke is white, without question. It seems to smoke constantly through the powerband, but it's less noticable at higher RPMs.
Lastly, the smoke has a very sweet smell to it.
Any ideas?
Here's the summary of what happened:
Purchased my 2000 Z-28 with 29K miles on it. It already had a P-1SC installed. First problem I had with the car was overheating. I overheated the car BADLY. I got the issue fixed up and I was on my way. Didn't have any other problems until the first time I was at the track this year (maybe 5 months after overheating).... I ran the hell out of the car. Then when I was sitting in the staging lane, my SES light started flashing. I didn't feel or hear misfires however.
Diagnostic tool said P0303 misfire.
I replaced the plug. The problem went away for a few days, then the code came back. Then the light turned off after a few days. Then it came back on. I read the code again and got a random multiple cylinder misfire code.
I pulled the #3 plug today. It was midnight black. I had only been running the car for less than two weeks. The only other symptom I can see is that after running, there will be just a bit of smoke that comes out of the exhaust. Kind of grey-ish smoke. And there's not a lot of it, and it only seems to come out when I'm idling.
What are my possible problems here? Could it be something as simple as the spark plugs (which haven't been changed in a long time) or wires or coil packs? Or is it something a tad more serious, like a head gasket (from overheating and then running really hard sometime later) or a warped head?
Any suggestions would be terrific.
BTW, the car had been run very hard after the overheating last year, and there were zero problems.
--------edit:----------
I checked the oil. The color is normal but it's very low. I replaced the 3rd spark plug (for the 2nd time) and I noticed that there was OIL on the bottom of the wire going to the plug.
Furthermore, the smoke is white, without question. It seems to smoke constantly through the powerband, but it's less noticable at higher RPMs.
Lastly, the smoke has a very sweet smell to it.
Any ideas?
Could possibly be a headgasket, If i were you, I would do a compression check on all the cylinders.
03-23-2006, 06:52 PM
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I would do a residual fuel pressure test...Pull all the plugs from the engine, check and see if any other ones are really black and sooty, If its just that plug on one cylinder..its possible you have a leaking injector, or it could be stuck open. This would obviously dump a huge amount of fuel into that cylinder, causing a misfire, and eventually fouling that one plug. Excessive fuel from this could also cause that grey-ish smoke you described earlier. Typically, greyish smoke is from excessive fuel. Also, has your coolant level dropped any?? Keep a close eye on that. Typically if your headgasket was leaking, this would cause you to run lean...If that plug was black, than it sounds like its def. running rich instead of lean..but i guess its to early to rule out anything..Good luck man, and let us know what you find out.
Last edited by Travis99LS1; 03-23-2006 at 06:59 PM.
