P0300 and P0308 help

NorCalLT1 · 08-18-2022, 10:01 PM

So this morning i drove my car to work and it felt fine then i felt like it began to sputter or miss. eventually the car threw a CEL and a stabilitrak error. I could tell the car was not firing on all cylinders. as i drove it home it would clear up intermittently and run fine then it would miss again. it cleared up a few times before i got home but ultimately the CEL was still on and i could tell it wasnt firing on all 8. My car did sit a few weeks prior to this. I ran my scanner and saw codes p0300 and p0308 misfires on cylinder 8. i swapped the coil to cylinder 2 but i never cleared the first code but when i rescanned there wasnt an issue on #2 so possibly not the coil. The plug on 8 looked fine. i dont know if this is a reliable way to check plug wires but i measured the resistance and #8 was the same as some of the other wires. any thoughts on what else i can do?

thanks

ctrlz · 08-19-2022, 06:02 AM

Is car modified?
Doubt it's plug or wires.
Check oil for any particulates or glitter suggestive of cam/lifter wear.
Would hook up a scanner and check fuel trims.
Possible bad fuel injector on #8.

NorCalLT1 · 08-19-2022, 11:36 AM

Should have mentioned that. Yes it's modified msd intake, rotofab, 95mm TB, tuned for e85

Ventmaster · 08-19-2022, 01:12 PM

Any room in the tank to top it off with fresh premium? Remember- KISS! Hopefully its a simple fix.

ctrlz · 08-19-2022, 01:51 PM

I would check the fuel trims.
Given the number of intake modifications, I would first guess air/vacuum leak causing the misfire. maybe the intake at the one corner since #8 is giving you trouble.

NorCalLT1 · 08-19-2022, 06:20 PM

I had just put new gas in it since it was pretty empty. Well now I'm very confused. I replaced the injector and the problem was still there. Now I'll admit I should have done this first and tried new plugs as it's least expensive but I did not think the problem was a spark plug due to the problem being intermittent. But here's why I'm confused, I switched the #8 and the #1 plug and now the car runs fine. No missing or sputtering and no CELs. I don't know why it would work in one cylinder and not the other

Ventmaster · 08-20-2022, 04:50 PM

Oh the unsolved mysteries and vagaries of life... Enjoy the ride while it lasts- and don't worry, be happy!

TurboVet · 09-17-2022, 09:30 PM

I had the same problem. Ran the car hard one night. The next day car ran like shit. Had codes p0300 and p0308. Changed plugs and wires and all is good.

08-18-2022, 10:01 PM	#1
NorCalLT1 Drives: SS Join Date: Aug 2019 Location: California Posts: 25	P0300 and P0308 help So this morning i drove my car to work and it felt fine then i felt like it began to sputter or miss. eventually the car threw a CEL and a stabilitrak error. I could tell the car was not firing on all cylinders. as i drove it home it would clear up intermittently and run fine then it would miss again. it cleared up a few times before i got home but ultimately the CEL was still on and i could tell it wasnt firing on all 8. My car did sit a few weeks prior to this. I ran my scanner and saw codes p0300 and p0308 misfires on cylinder 8. i swapped the coil to cylinder 2 but i never cleared the first code but when i rescanned there wasnt an issue on #2 so possibly not the coil. The plug on 8 looked fine. i dont know if this is a reliable way to check plug wires but i measured the resistance and #8 was the same as some of the other wires. any thoughts on what else i can do? thanks

08-19-2022, 06:02 AM	#2
ctrlz Drives: 2017 2SS, 50th pkg, M6, MRC, NPP Join Date: Jan 2016 Location: Ocean City, NJ Posts: 3,162	Is car modified? Doubt it's plug or wires. Check oil for any particulates or glitter suggestive of cam/lifter wear. Would hook up a scanner and check fuel trims. Possible bad fuel injector on #8.

08-19-2022, 11:36 AM	#3
NorCalLT1 Drives: SS Join Date: Aug 2019 Location: California Posts: 25	Should have mentioned that. Yes it's modified msd intake, rotofab, 95mm TB, tuned for e85

08-19-2022, 01:12 PM	#4
Ventmaster Drives: 2017 1SS 6spd Join Date: Jan 2011 Location: Utah Posts: 2,857	Any room in the tank to top it off with fresh premium? Remember- KISS! Hopefully its a simple fix.

08-19-2022, 01:51 PM	#5
ctrlz Drives: 2017 2SS, 50th pkg, M6, MRC, NPP Join Date: Jan 2016 Location: Ocean City, NJ Posts: 3,162	I would check the fuel trims. Given the number of intake modifications, I would first guess air/vacuum leak causing the misfire. maybe the intake at the one corner since #8 is giving you trouble.

08-19-2022, 06:20 PM	#6
NorCalLT1 Drives: SS Join Date: Aug 2019 Location: California Posts: 25	I had just put new gas in it since it was pretty empty. Well now I'm very confused. I replaced the injector and the problem was still there. Now I'll admit I should have done this first and tried new plugs as it's least expensive but I did not think the problem was a spark plug due to the problem being intermittent. But here's why I'm confused, I switched the #8 and the #1 plug and now the car runs fine. No missing or sputtering and no CELs. I don't know why it would work in one cylinder and not the other

08-20-2022, 04:50 PM	#7
Ventmaster Drives: 2017 1SS 6spd Join Date: Jan 2011 Location: Utah Posts: 2,857	Oh the unsolved mysteries and vagaries of life... Enjoy the ride while it lasts- and don't worry, be happy!

09-17-2022, 09:30 PM	#8
TurboVet Drives: Corvette Join Date: May 2016 Location: New Albany Posts: 45	I had the same problem. Ran the car hard one night. The next day car ran like shit. Had codes p0300 and p0308. Changed plugs and wires and all is good.

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