Help! I have a p0300 code!!!
Thread Starter
Racer
Joined: Jun 2010
Posts: 360
Likes: 0
From: Chicago Illinois
Help! I have a p0300 code!!!
So I was driving my car and did a pull from 1st gear to 4th and once I slowed down my rpms stayed at 1200 and once I pulled over and stop, the car started to surge and the idle sounded very slow and weird. Almost like i had a very large cam that was struggling to stay alive. I checked my codes and it threw a 10-PCM P0300 H C and only that. I got the car home and started it the next day....same sound. I know that the code is a random misfire but im going to run a diagnostic on it today to see exactly whats wrong. Has this ever happened to anyone?
Tech Contributor
Joined: Jan 2007
Posts: 19,398
Likes: 1,139
From: Dyer, IN
Sure, and if you do a search for P0300, you'll see that. No rocket science here. Pull your codes to see if it will isolate to a cylinder. If not, check plugs and wires(especially since you have headers). A condition of a plug can help isolate a misfiring cylinder as well.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Absolutely sounds like a misfire---Most scanners will isolate the exact cylinder but I would change ALL the plugs and wires regaurdless
My experience is that people get lulled into thinking that today's spark plugs can go 100K- Maybe---But common sense dictates that even platinum, plugs should be checked every 25-30K miles---ESPECIALLY a modded car with hds/cam/or LT's--
With LT's you could have a wire thats gone bad from being too close to the header tube
My reccmd is to go with the NGK TR55 plugs gapped at .040 and I really like the GM perf(red) wires or the Taylor T-50
LT's open up a whole new can of worms---Short answer is that they make your engine run overly rich during part throttle ans may afect yout WOT fueling as well ---I would a never consider installing LT's without getting a REAL tune---You may even be getting LESS HP or very little unless you tune it--The full potential of your LT's cannot be achieved without a tune---AND its running rich--(could be the reason for your fouling plugs as well----
My experience is that people get lulled into thinking that today's spark plugs can go 100K- Maybe---But common sense dictates that even platinum, plugs should be checked every 25-30K miles---ESPECIALLY a modded car with hds/cam/or LT's--
With LT's you could have a wire thats gone bad from being too close to the header tube
My reccmd is to go with the NGK TR55 plugs gapped at .040 and I really like the GM perf(red) wires or the Taylor T-50
LT's open up a whole new can of worms---Short answer is that they make your engine run overly rich during part throttle ans may afect yout WOT fueling as well ---I would a never consider installing LT's without getting a REAL tune---You may even be getting LESS HP or very little unless you tune it--The full potential of your LT's cannot be achieved without a tune---AND its running rich--(could be the reason for your fouling plugs as well----
Le Mans Master
Joined: Nov 2005
Posts: 6,993
Likes: 25
I would also suspect a valve spring bought it here. Pull the valve covers for a "peek".
I believe the code from the DIC will only show P0300, you'll need another scanner to see if there are any p030[1-8] codes.
I believe the code from the DIC will only show P0300, you'll need another scanner to see if there are any p030[1-8] codes.
Last edited by dougbfresh; Sep 15, 2010 at 04:15 PM.
Melting Slicks
Joined: Mar 2007
Posts: 2,158
Likes: 1
From: Always In Front, Colorado
I got the exact same code after doing a quick 3rd gear pull to 100 mph, (02 Z with procharger) Once I got into town and started giving it some gas it was running as if it was on 7 cylinders. At idle and revving it a couple times it sounds ok, but under load you can tell something is not right. Suppose I will start looking into it this weekend, starting with plugs, then wires and if that is not it, I'll pull valve covers looking at the springs.. The internals of the engine are all stock and it has around 28K miles on it.. Of which 15K has been under boost..
Fun times.
Fun times.
Race Director
Joined: Aug 2002
Posts: 18,254
Likes: 1
From: Deep in the Heart o' Texas
St. Jude Donor '09-'10-'11-'12-'13
All of the above responses are good ones. I had a similar situation with the P0300 code too. It was a precursor to failed front O2 sensors. Eventually codes P0171 and P0174 would appear with the same symptoms as the original P0300 code. In my case, almost 80K miles with LT headers took its toll on the O2's and they needed to be replaced. Since the replacement of the O2's, no problem at all. Mind you I'm not implying this is the problem with your car but only a passing on of my situation. Good luck with the fix. 
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Drifting
Joined: Jan 2008
Posts: 1,722
Likes: 138
From: Florida
St. Jude Donor '09
Absolutely sounds like a misfire---Most scanners will isolate the exact cylinder but I would change ALL the plugs and wires regaurdless
