Help with code P0300 - Car runs terribly!
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Launching!
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From: Upstate South Carolina
Help with code P0300 - Car runs terribly! My car all of the sudden started with a slight misfire on the freeway that gradually got worse until the point that the car would misfire, skip, pop,and sputter when driving. My check engine light then came on when I was at a stop, when I started driving again the CEL started blinking. I scanned the code and got a P0300 multi cylinder misfire code. I pulled the #2 plug and was solid black. I then pulled the driver's 02 sensor and it was also solid black. The other plugs look fine, and the driver's 02 sensor was fine.
Today I changed the passenger 02 sensor and reset the ECM. I still have the same problem. Car still backfires, pops, etc. Someone please give me some advice on what to do next.
Today I changed the passenger 02 sensor and reset the ECM. I still have the same problem. Car still backfires, pops, etc. Someone please give me some advice on what to do next.
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Joined: Dec 2001
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From: Jacksonville, FL
P0300 can be a PITA to diagnose if you don't have a scanner. Mine has thrown it a couple times over the years, but was fine after clearing it. Visit gearchatter.com First thing I'd do is plugs/wires if you're not getting any other codes.
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Thread Starter
Launching!
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From: Upstate South Carolina
Originally Posted by chevyhighrider
So what exactly have you replaced so far, did you change both O2's out with new ones yet?
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From: Michigan
I have searched around for other people with the same problem you are having, the most common things that I found were: plugged fuel injectors, bad coil(s), bad wire(s), bad or cracked spark plug(s), cracked vacuum lines, faulty map sensor, plugged EGR. I would try running some fuel injector cleaner through with some premium and if that doesn't work look into the other things. The way it sounds though it doesn't really sound like a fuel starvation problem, but it is cheap for a bottle of injector cleaner.
Does it have a definite miss at idle? If it does, the first thing you need to do is pin it down to the cyl. If you dont have bi-directional control with the PCM the next best way is to, one at a time, unplug either each injector, or each coil, while its running. After you figure out which cyl., then you just need to check for good spark THROUGH the wire (good coil, good wire). Check your plug, make sure its not cracked or anything. If it was running just fine then this happened I wouldnt think its an injector failure, but its possible. Also may want to pull the VC on the side with the bad hole. It may have bent a pushrod, broke a rocker bolt or something like that.
02 sensors, even if they're bad arent gonna cause a P0300, unless its dumping so much fuel it totally fouls a plug. But then all the plugs on at least one bank would be fuel fouled.
02 sensors, even if they're bad arent gonna cause a P0300, unless its dumping so much fuel it totally fouls a plug. But then all the plugs on at least one bank would be fuel fouled.
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Launching!
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All the plugs on the passenger side are solid black, and all of the plugs on the driver's side are normal. It does have a definate miss at idle. It also backfires through the exhaust every now and then. Both oxygen sensors have been replaced, the passenger side is solid black, the passenger side is normal. So obviously one of cylinders 2, 4, 6, and 8 are where the problems are would you agree?
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With the car turned off use a voltmeter and check the black wires on each coil (2,4,6,8), by setting the meter to ohms and verifing that there is a connection to ground for each one. If you are not familiar with how to do this, place the black probe on a good ground(battery ground or any metal part on the car respectively) and the other red probe on the black wire coming off of a coil. The meter should read somewhere close to zero, repeat this with the other coils as well. If that checks out ok then turn the ignition on (with the engine off) and check the pink wire on the coil connectors for voltage, (red probe on pink wire and black probe on ground). Let me know what you find.
Last edited by chevyhighrider; Jan 7, 2007 at 03:50 PM.
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Launching!
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I checked all the coils, and they are all good, but I did unplug an injector, and the car ran the same way. I unplugged random injectors on the driver's and passenger's side and it ran the same. If it is an injector problem, why are my plugs on the passenger side solid black?
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Launching!
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Descreened the MAF not long ago, I actually was just picking up the car from getting a new starter when it started happening. It ran fine for a few miles, and then started running like that.
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Launching!
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Well, the car is fixed. I wish I knew what fixed it. It was pouring down rain when the problem started so I am thinking water got in something. I replaced both oxygen sensors after finding a little water in the passenger side 02 connector, maybe that explains why the plugs were black on the passenger side. I added some BG 44K fuel system cleaner and drove it home for lunch and I noticed it ran alot better. After the car sat and I drove it back to work, the SES light went off? I have no clue, but the car seems to be fixed. Thanks to everyone for the help.
Robbie
Robbie