P0300 Code,misfiring on 2,3,5,6,8 cylinders
04-02-2011, 04:30 PM
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Staging Lane
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P0300 Code,misfiring on 2,3,5,6,8 cylinders I've searched on here last night and today, and have came to numerous conclusions. I'm asking you guys since the dealership doesn't want to look at this too much since it has a "professional products" intake manifold on it. It does have the aftermarket fuel rails with it and appears to be the stock injectors. I just bought this car 30 days ago. The service engine light has been on since I bought it. Dealership said it's the catalytic converter so I had it replaced with a new factory one. Well, the light never turned off, mechanic said the P0300 code is still on, misfiring on said cylinders, and shows running lean on banks 1 and 2.
You can feel it almost wanting to stall out when you come to a stop at a traffic light. When you get on the throttle it's fine. But you can tell there is a miss. My !st conclusion would be an o2 sensor on the side the driver side? The previous owner had pass. side converter and 02 sensor replaced last year. So I'm guessing driver's side to be the culprit. Any advice would be appreciated by you guys, since mechanics are scared to look at it. Btw..the previous owner, when I talked to them, said the intake was done a few years ago, and it's always been fine, so I don't think that's the issue. Not like they just put it on and forgot to put a vacuum line on or something. And she said that is the only aftermarket part on the car. Everything else is stock and never had a tune done. Thanks in advance, guys.
You can feel it almost wanting to stall out when you come to a stop at a traffic light. When you get on the throttle it's fine. But you can tell there is a miss. My !st conclusion would be an o2 sensor on the side the driver side? The previous owner had pass. side converter and 02 sensor replaced last year. So I'm guessing driver's side to be the culprit. Any advice would be appreciated by you guys, since mechanics are scared to look at it. Btw..the previous owner, when I talked to them, said the intake was done a few years ago, and it's always been fine, so I don't think that's the issue. Not like they just put it on and forgot to put a vacuum line on or something. And she said that is the only aftermarket part on the car. Everything else is stock and never had a tune done. Thanks in advance, guys.
04-02-2011, 11:20 PM
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Welcome to Bendover County. If all you have is a dealership
mechanic's word for what's up, you're going nowhere but broke.
Putting an intake on it and nothing else, would be a pretty
dumb move. I'd suspect that the thing may have more mods
than said.
However, early Pro Products gaskets were not great, they
updated them and fixed a tendency to have vacuum leaks.
If you see green intake-head gaskets consider asking
Pro Products for a replacement set, they should be cheap
enough. Also check that the valley cover bolts have been
replaced with button head types, stock hex head can make
the manifold not seat (maybe somebody found another way
to "fix" the situation).
If you want to check for leaks it will be tough without
control of the IAC and adaptive spark that try to hold
idle steady. Stealership could do that, so could anybody
with decent tuning software. But it might be worth a can
of carb cleaner to try.
mechanic's word for what's up, you're going nowhere but broke.
Putting an intake on it and nothing else, would be a pretty
dumb move. I'd suspect that the thing may have more mods
than said.
However, early Pro Products gaskets were not great, they
updated them and fixed a tendency to have vacuum leaks.
If you see green intake-head gaskets consider asking
Pro Products for a replacement set, they should be cheap
enough. Also check that the valley cover bolts have been
replaced with button head types, stock hex head can make
the manifold not seat (maybe somebody found another way
to "fix" the situation).
If you want to check for leaks it will be tough without
control of the IAC and adaptive spark that try to hold
idle steady. Stealership could do that, so could anybody
with decent tuning software. But it might be worth a can
of carb cleaner to try.
04-03-2011, 07:56 PM
#6
1st thing you need to do is pull the intake and replace the gaskets......don't even both trying anything else until you do. Be sure you understand how to install them and why it needs to be sealed properly.
04-03-2011, 10:09 PM
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Staging Lane
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According to the lady's brother, the original LS1 intake had several leaks, and he ran across a good deal on this new Professional products intake. Now, just last year, she had the pass. side cat and o2 sensor replaced, which she said the car was stuttering when it came to a stoplight when those parts needed replaced. Same thing it is doing now. I had the cat replaced, but the 02 is still the old one. Would it be possible for it to be bad? Or would it throw some type of an 02 sensor code if it went bad?
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04-04-2011, 01:28 PM
#8
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Codes do not mean the sensor is bad, the tests can be
spoofed (such as, by bad vacuum leaks among other
things). But O2s can also be killed early by stuff like so
much leakage air in one cylinder that it overfuels the
other three to get the "right answer" and you soot it
up in no time.
Throwing parts at it blind, is a bad way to spend your
dough. Start with what's different and make sure it's
not the problem (manifold). And find a way to get some
sort of scan capability (even used AutoTAP). It should
cost you way less than a shopping basket of random
irrelevant parts.
spoofed (such as, by bad vacuum leaks among other
things). But O2s can also be killed early by stuff like so
much leakage air in one cylinder that it overfuels the
other three to get the "right answer" and you soot it
up in no time.
Throwing parts at it blind, is a bad way to spend your
dough. Start with what's different and make sure it's
not the problem (manifold). And find a way to get some
sort of scan capability (even used AutoTAP). It should
cost you way less than a shopping basket of random
irrelevant parts.
04-08-2011, 08:22 PM
#9
Staging Lane
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Ok, so I looked at the gaskets, and they're black. So they must be newer. The service engine light is now flashing for approximately 5-10 seconds after running the car for about 10 minutes. And everytime is has started flashing has been under acceleration. I've been driving the car very little until I get someone to look at it, or one of you guys know what's wrong, or a good clue anyways. Something I've noticed since the replacement of the converter a week ago....the rpm's seem to stick after revving the car when in park. If I start the car, leave it in park, rev car to 3,000 RPM, the rpm's seem to take about 10 seconds until it goes back to idle. And as said, after letting it idle for alittle bit, it's very rough.
I told a mechanic the situation and he said "maybe the heads are bad". I know that's not the case. And the car ran fine before the car had the new converter put on! Sure, the service engine soon light was on, but it ran fine.
There's no way I put a new converter on and it caused all these issues!! Help would be greatly appreciated guys. I'm getting ready to go on vacation, and I don't have hundreds of dollars to spend on just "diagnosing the problem".
I told a mechanic the situation and he said "maybe the heads are bad". I know that's not the case. And the car ran fine before the car had the new converter put on! Sure, the service engine soon light was on, but it ran fine.
There's no way I put a new converter on and it caused all these issues!! Help would be greatly appreciated guys. I'm getting ready to go on vacation, and I don't have hundreds of dollars to spend on just "diagnosing the problem".
04-08-2011, 08:43 PM
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New converter as in smaller diameter, lighter weight, causes false
misfires a lot of the time.
Misfires under load can be a bad plug wire or coil but that would be
consistent to the affected cylinders and show up in scanning.
misfires a lot of the time.
Misfires under load can be a bad plug wire or coil but that would be
consistent to the affected cylinders and show up in scanning.
04-30-2011, 04:22 PM
#12
Staging Lane
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Jimmyblue, you were right. The intake gaskets were the problem. They were even the updated black gaskets though. The gaskets looked like they were wet. Keep in mind I just got the car 45 days ago. I believe whoever had the car before me had been really letting the intake have it with a hose, pressure washer,something. It wasn't antifreeze or anything like that. Definitely water. there also was a vacuum leak in the back that was unattached from the A.I.R. The car is running great now, and hopefully this gasket set will last longer. I put the Professional Products updated gasket back on it. The car runs like new again!! Thnaks alot for the help guys!
