P0300
01-10-2013, 06:51 PM
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P0300 I am getting the random misfire code. It only occurs at freeway speeds. I have checked for vacuum leaks and found none. Checked plug wires only one seemed a little loose. They are all new plugs and wires but that was well over a month ago and the code just started to occur. They are gaped correctly as well.
Only thing is I found that the Bank 2 front O2 reads around 0-4mV while the key is in the on position but Bank 1 reads around 80 or so mV. Could this be a bad O2? I don't want to cough up the money but it is the only old one on the car... the others are all less then a year old. Also when the car is running the O2s seem to read similar values all around.
Only thing is I found that the Bank 2 front O2 reads around 0-4mV while the key is in the on position but Bank 1 reads around 80 or so mV. Could this be a bad O2? I don't want to cough up the money but it is the only old one on the car... the others are all less then a year old. Also when the car is running the O2s seem to read similar values all around.
01-10-2013, 07:07 PM
#2
Random misfire I have found is almost always a vacuum leak somewhere or you've got a wire thats arching or something. If its only at highway speeds, is it when you hit a bump or does it do it at a smooth cruising speed? try moving the wires around while the car is running.
If its an 02 sensor, see if you can grab a buddies and drive it around, see if it still does it..or one from a pick-n-pull used but working. If my CEL comes on after scanning it with my reader, I just use this site to check the basics...
http://www.obd-codes.com/p0300
If its an 02 sensor, see if you can grab a buddies and drive it around, see if it still does it..or one from a pick-n-pull used but working. If my CEL comes on after scanning it with my reader, I just use this site to check the basics...
http://www.obd-codes.com/p0300
01-10-2013, 07:50 PM
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It does it flat straight whatever just on the freeway at freeway speeds. I don't think it is plug wires since it is the p0300 which means more then one cylinder. I checked again for vacuum leaks nothing. It idles perfect, has full power, doesn't hesitate, doesn't miss when I throttle it or let it decelerate. The fuel filter is new changed that about 4 months ago and fuel pressure is up. Is their something else I am missing i.e why it does it on the freeway not in town driving.
01-10-2013, 09:01 PM
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If you have 4 O2s, then swap the rears with the fronts. A bad front O2 can alter engine performance, but if you have a bad one in the rear itll just throw a code and leave performance alone. If it fixes it, you know one of your rear O2s is now bad. You could try cleaning the MAF as well and check the air filter
01-10-2013, 09:03 PM
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I took it in the first time and that was the problem, then it did it 4 months later and I just disconnected one on each side and it worked! I have no cats and its not tune so the check engine light don't bother me! Lol
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01-11-2013, 08:15 AM
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No, it wouldnt. The fronts are used to adjust fuel trims where the rears are just a check. If the fronts are bad, your fuel trims could be misadjusted but if the backs are bad, it will just throw a check engine light telling you your cat efficiency is low. In that case, you would get a P0420 or P0421 code.
I had two vehicles with a P0300 code in the past. One had a bad intake gasket that lead to the smallest of leaks. The other was a dirty/clogged fuel system as the result of a tank of bad gas. Had the shop do a specialty high pressure clean of the system and all was well.
I had two vehicles with a P0300 code in the past. One had a bad intake gasket that lead to the smallest of leaks. The other was a dirty/clogged fuel system as the result of a tank of bad gas. Had the shop do a specialty high pressure clean of the system and all was well.
01-11-2013, 02:40 PM
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I feel like my front 02 is bad because when I scan it the O2 reads 0-4mV for like the first 3 minutes of warm-up while the other is reading around 70-90mV sometimes spiking like normal. Also the O2 heater monitor will not run and all that takes is a warm-up from a cold start...didn't work twice now.
01-13-2013, 08:08 PM
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I replaced the 02 sensor I thought had some funny readings...well after the new 02 the reading were a little better but I still have the misfire code. Next I am gonna try a relearn on the crank with my HP-tuners see if that helps it.
I want to update what I have done in hopes this may help someone else.
I want to update what I have done in hopes this may help someone else.
01-15-2013, 06:10 PM
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So... I did the relearn and nothing much came of it. Once again I cleared it and at idle it will not come up. Used a histogram with HP and it says timing advance is high, 0 for knock retard (good), LTFT reads high mostly in the 9's with a 12 being highest, STFT reads a 5 as the highest, but the Narrowband shows that on the graph manifold pressure vs rpm its showing some really low values like 9 and 8 on the lowest rpm column which is .4.
So basically does this mean a vacuum leak in the manifold if the pressure is too low?
So basically does this mean a vacuum leak in the manifold if the pressure is too low?
01-16-2013, 09:50 PM
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Update: I figured out the misfires are on cylinders 2 and 3 and they only occur with freeway speeds rpm doesn't matter. I am thinking failing coil packs. I am gonna swap them around tomorrow and see if the misfires move cylinders. Tomorrow is my birthday so wish me luck.
01-17-2013, 02:41 PM
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Not coil packs after switching them the misfire stayed. I did get a new tank of gas and injector cleaner and the number of misfires went down by about half over the same trip same driving style. Next I am gonna check plugs.
01-17-2013, 03:26 PM
#16
how did you pin point the 2 cylinders as the culprits? are you now getting 302/303 CELs?
My truck had a bad misfire and eventually threw a code. Then it started running really rough. Turned out my fuel filter crapped out on me. New fuel filter fixed it. Then my s/c cavalier had a random misfire (P0300) and it was the intake manifold gasket. New gasket fixed that. I also had a fuel system open circuit CEL due to one of my injector wires being pulled too much and basically splitting it inside the protective wire covering.
Basically you just gotta recheck all your steps, write it all down and paint a brief picture of whats been done so others can suggest something you havent thought of.If its affecting neighboring cylinders...is it possible you have low compression in one of your cylinders due to a leak? Have youd one a compression test?
My truck had a bad misfire and eventually threw a code. Then it started running really rough. Turned out my fuel filter crapped out on me. New fuel filter fixed it. Then my s/c cavalier had a random misfire (P0300) and it was the intake manifold gasket. New gasket fixed that. I also had a fuel system open circuit CEL due to one of my injector wires being pulled too much and basically splitting it inside the protective wire covering.
Basically you just gotta recheck all your steps, write it all down and paint a brief picture of whats been done so others can suggest something you havent thought of.If its affecting neighboring cylinders...is it possible you have low compression in one of your cylinders due to a leak? Have youd one a compression test?
01-17-2013, 05:28 PM
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I have HP tuners software and it shows misfires on specific cylinders... They are high counts too... I am driving it really gently to 50 on the freeway and they start. I have now swapped plugs, wires, coils and re-gaped. The misfires stayed on those 2 cylinders so next I am gonna do a compression check. If that's OK then I know its a fuel injectors thing or its manifold gasket time and if those fail I am selling the car for a $1. Thanks.
01-19-2013, 02:39 AM
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Bad news bacon... the injectors were cleaned but the guy said they were spotless to begin with. So ...I am gonna just change the intake manifold gasket and pray. The car does run at like 30kpa at idle idk if thats too much vacuum or what but I have heard much higher numbers. Its also around 30kpa or so when I drive only time it jumps is when I punch it and I get around 100kpa.
