Random Misfire. P0300
07-09-2011, 08:22 AM
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Random Misfire. P0300
Thursday night my car started missing. It caught me by surprise because I haven't had a single issue out of it. I just drove it on a 60 mile round trip Wednesday evening and it sat all day Thursday until I drove it that night and it started missing. I replaced the plugs yesterday afternoon with NGK Iridiums and it didn't fix it. I cleaned the MAF sensor and it didn't fix it. I have physically looked the entire motor over for anything out of the ordinary and found nothing. I really didn't want to just start replacing sensors until I found the right one because that will get expensive. Any suggestions?
07-09-2011, 11:55 AM
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I have been messing with it all day. Put some fuel system cleaner in it and still no fix. Also went back and checked all of my plugs again and they all look the same with a mild chalkiness so I have no idea which cylindar is messing. I really need some suggestions.
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07-09-2011, 12:44 PM
#8
did you do any changes on the car recently? any mods or anything?
best thing to do is get with some one in ur area that has a cipher cable.. that will tell you alot.. but other things to check for
Bad gas
air/fuel mixture is running lean
vacuum leak
dirty injectors
low fuel pressure
weak ignition coil?
compression problems
best thing to do is get with some one in ur area that has a cipher cable.. that will tell you alot.. but other things to check for
Bad gas
air/fuel mixture is running lean
vacuum leak
dirty injectors
low fuel pressure
weak ignition coil?
compression problems
07-09-2011, 01:36 PM
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It was running perfectly before, thats why I'm not sure where to start. I did put some fuel system cleaner in and put more gas in. I had filled up half a tank and drove a good 70 miles before it started. How can I test the coil packs? Do I need to buy a new one and start replacing them one at a time? I do not have a vacuum leak. I sprayed soapy water everywhere. I want to try to fix this with minimal cost as I have been trying to sell it.
07-09-2011, 01:37 PM
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I did have a pop charger on it and it was fine but I took it off and sold it a few hundred miles ago and it was fine then also. I might try cleaning the maf again. If it was a specific coil or specific injector wouldn't tell me P030x for that specific cyclindar instead of P0300?
07-09-2011, 01:52 PM
#11
Its most likely your maf sensor. My friend had the same exact problem.
Usually when its a bad coil pack or sensor you will get a PO300 along with a PO30x at the same time. If you know someone else with a Z just switch maf sensors and see if the prob goes away.
Usually when its a bad coil pack or sensor you will get a PO300 along with a PO30x at the same time. If you know someone else with a Z just switch maf sensors and see if the prob goes away.
07-09-2011, 02:05 PM
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^ Thanks. Its definitely worth a shot. I tried cleaning it already but it might be bad. Wouldn't the SES light stay on constant if it was a bad sensor? The light will be off when I start the car but once I start driving, it comes on and then starts flashing and then will be off when I start the car again.
07-10-2011, 02:42 AM
#15
It's a bad fuel injector. It should be closing before the valve but it can't and the fuel it sprays bounces off the closed valve and blows up into the plenum and gets sucked in by the other cylinders. The engine senses the overly rich condition and thinks it's misfiring and throws a PO300. Pull all your spark plugs and inspect them one by one. Whichever is carbon fouled, that's your stuck injector, change it.
Last edited by Lawn Dart; 07-10-2011 at 02:45 AM.
07-10-2011, 10:32 AM
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It's a bad fuel injector. It should be closing before the valve but it can't and the fuel it sprays bounces off the closed valve and blows up into the plenum and gets sucked in by the other cylinders. The engine senses the overly rich condition and thinks it's misfiring and throws a PO300. Pull all your spark plugs and inspect them one by one. Whichever is carbon fouled, that's your stuck injector, change it.
07-10-2011, 02:06 PM
#17
^ the plugs might be fine but..you need to do what he says it could be one of your injectors..
I believe what you need to do is.. run the car for a bit then immediatly shut it off.. Then take out ur new spark plugs and see which one is fouled if any
I believe what you need to do is.. run the car for a bit then immediatly shut it off.. Then take out ur new spark plugs and see which one is fouled if any
07-10-2011, 08:23 PM
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I pretty much did that. They all looked the same. I will do it agian tomorrow and let it run longer. They all had a mild chalkiness on the tips.
07-11-2011, 08:01 AM
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Well I just went out to mess with it some more. I let the car run for almost 30 minutes and then gave it some revs and immediately cut it off. Also while it was running I unplugged the MAF sensor to see if there was a difference and there was so the MAF should be good. I went through and started checking the plugs. I have been suspicious about cylindar 2 so I started with it and the plug was practically clean and wet with fuel. The rest of the plugs now had a mild blackish brown color like they should.
My question is, injector or coil pack? Obviously there is fuel in there but maybe no spark?
My question is, injector or coil pack? Obviously there is fuel in there but maybe no spark?
07-14-2011, 08:05 PM
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My new injector finally came in. I replaced it but there is still a problem. I will admit, the car seems to be running better. It is actually driveable now but there is still a small miss. At least it actually goes when you give it gas. I'm going to recheck all of my plugs again tomorrow and recheck all the gaps. Really need to get her back on the road. Actually getting tired of riding my bike haha.