PO300 code
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Teching In
Joined: Sep 2003
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PO300 code Im getting a multi random cylinder miss fires. I have used GM top engine cleaner changed plugs and wires. Have no clue where to go from here. the miss seems to get worse with the warmer the car gets warm. I have also had the injectors cleaned. Please tell me where to go from here.
Re: PO300 code I agree that there are few places for vacuum leaks on a LS1 just check around the intake manifold or possible around an injector, or EGR system. Just trying to help. 
Re: PO300 code I have the same problem in my siverado. It started right after cam install. Maybe I disturbed a seal or hose and caused a vacuum leak.
The cam I put in was small enough that it was not supposed to upset idle to the extent that it has.
The cam I put in was small enough that it was not supposed to upset idle to the extent that it has.
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Re: PO300 code I get the P0300 on my Silverado too after I did a cam install, but it resets itself pretty quickly. The first time the SES came on I cleared the code with AutoTap, but the MIL still comes back on. Before I can reset it the PCM clears the code on its' own. I only get the code after a cold start when the engine hiccups while trying to warm up. My LSA is 112 so that may be why I sometimes get the P0300 DTC. As far as the vacuum leak you should use a gauge to check for erratic reading. It will be apparent if that is the cause by the gauge reading. Locating the leak will be the hard part. Go back over any work you have recently done and check all hoses and their connection points.
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Teching In
Joined: Jun 2015
Posts: 5
Likes: 0
From: Ont canada
Hey guys I just came across post and I'm dealing with this proplem right now ...
I have a lq4 6.0 with a set of ported 317 heads with the comp cam 54-459-11 camshaft. With a set forged wisco pro piston the motor is killer I just finished all the ecm tuneing today but up till this point I have been getting po300 code at idle in drive my tuner says he thinks it's the camshaft but after seeing on here it could be a battery? ?? Has anyone ever come across this with this cam input needed
I have a lq4 6.0 with a set of ported 317 heads with the comp cam 54-459-11 camshaft. With a set forged wisco pro piston the motor is killer I just finished all the ecm tuneing today but up till this point I have been getting po300 code at idle in drive my tuner says he thinks it's the camshaft but after seeing on here it could be a battery? ?? Has anyone ever come across this with this cam input needed
Hey guys I just came across post and I'm dealing with this proplem right now ...
I have a lq4 6.0 with a set of ported 317 heads with the comp cam 54-459-11 camshaft. With a set forged wisco pro piston the motor is killer I just finished all the ecm tuneing today but up till this point I have been getting po300 code at idle in drive my tuner says he thinks it's the camshaft but after seeing on here it could be a battery? ?? Has anyone ever come across this with this cam input needed
I have a lq4 6.0 with a set of ported 317 heads with the comp cam 54-459-11 camshaft. With a set forged wisco pro piston the motor is killer I just finished all the ecm tuneing today but up till this point I have been getting po300 code at idle in drive my tuner says he thinks it's the camshaft but after seeing on here it could be a battery? ?? Has anyone ever come across this with this cam input needed
Teching In
Joined: Jun 2015
Posts: 5
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From: Ont canada
PO300 code Ya I hear ya like I said the final tuneing was done today so we will see . Well I was having this po300 come up the ecm was only on a bench tune all the data logging was done and finished today .....So for I am new this ecm tuning this can be fix by tuneing the guy who did the tuneing is mgs performance he has been around for 20 plus years let hope he knows what he's doing
