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420A P0300 error code

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RJ_IS_BATMAN

Proven Member
105
19
May 7, 2020
Ontario, California
Hey everyone,

So driving back on the freeway today I had my check engine light turn on, checked it whe I got home and it’s the P0300 code.

I changed the spark plugs with ngk plugs, ngk spark plug wires and an msd Ignition. Car runs great no issues at all, no loss of powers or anything.

The previous owner did straight pipe the car and removed the catalytic converter, could this be what’s causing the issue due to no cat to help with the exhaust fumes?

any help would be appreciated
 
I believe that is the random misfire code. Also tripped by lightweight flywheels sometimes. If the car isn't actually misfiring, the code should be deleted. Most people won't need a CEL to know if they have a misfire anyway.

If the car is actually misfiring, then diagnose like a standard misfire. (Plugs, wires, coils, crank sensor are all things to check).
 
Thanks for the info, that’s what I thought as well, I was just cruising on the freeway when it happened but no symptoms of any issues just came on but car ran great still so odd
 
Yeah, P0300 while cruising at freeway speed and no obvious misfire -that sounds like its being tripped by a lightweight flywheel setup.

Simplest remedy is to have the P0300 code "erased" through tuning.

EDIT: totally didn't see this was 420A. Might be different that 4G63, but what I posted is relevant to the 4G63 cars. May or may not apply.
 
I cleared the code and checked the spark plugs and they were a bit loose so i tightened them up. Took the car on the freeway and no CEL light came on... But then my oil light came on and started blinking off and on randomly. Checked the oil and its fine its not low at all. I thought my misfire issue was resolved but it came on again this time just driving on the street at like 30mph and again no stalling, no hesitation or sputtering. Its the oddest thing.
 
Your oil light could possibly be caused by the connector being loose and wobbling back and forth. It's a crappy location for it and a poor design to start with. Have you replaced your O2 sensor recently or need one? I've had those cause a misfire code in the past. Unless you get a p0301-p0304, I wouldn't worry about the cylinders actually misfiring. It's likely to be something else that doesn't specifically have a code, but uses p0300 as a default code. Is there any problems your car has been having in other locations?
 
Your oil light could possibly be caused by the connector being loose and wobbling back and forth. It's a crappy location for it and a poor design to start with. Have you replaced your O2 sensor recently or need one? I've had those cause a misfire code in the past. Unless you get a p0301-p0304, I wouldn't worry about the cylinders actually misfiring. It's likely to be something else that doesn't specifically have a code, but uses p0300 as a default code. Is there any problems your car has been having in other locations?

I did some searching and saw that it is a common issue and figured that the oil connector could be loose or the sensor itself might need to be replaced, the car sat for a while before I got it and slowly I’m fixing all the issues the prior owner neglected. As for the O2 sensor, I haven’t replaced either sensor, the car is straight piped and there’s no error code coming up for that so i wasn’t sure if the car being careless is causing some issues
 
Yes, I apologize for that error, my autocorrect changed that. The car is catless so I wasn’t sure if that would also cause issues.. I figured I would get an O2 sensor code though due to the straight piped exhaust.
 
No worries, just wanted to make sure I was following what you meant. I forgot to notice your car was NA. The basic idea should still apply though. As far as catless though, I'm not sure how that would be different between the ECU's parameters between turbo and non-turbo. On the turbo cars, the downstream o2 is just a narrowband that doesn't really do much beyond sitting in the bung. I would imagine that it might be the same for your car, but not 100% positive. In all the times I've had no cat on my cars, I've never had any downstream o2 problems, but have had many times where the upstream o2 caused issues because it was dirty with carbon. Might be something worth checking out if you have free time for it.
 
Hey all, I’m having a similar issue in my vehicle and I can’t seem to figure out what the issue is. Originally had the p0300 + misfires detected in 2 cylinders. Installed new NGK spark plugs, wires and coil, then had my downpipe, flex pipe (went bad), cat & both 02 sensors replaced new. Car ran fine and no more error codes.
Then today (about 2 months after repairs) I drove about 250 miles between 65-7mph with no issue, but on the return trip the CEL came on while going 75mph and my reader showed p0300 as well as misfires detected in all 4 cylinder. (see image below).
Any idea what could be causing it?

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Check your camshaft & crankshaft position sensors. If they appear to need replacement, do not use an Ebay part. Buy a trusted name brand. Also be sure the connector for your coil is clean and tight.

I'm assuming you checked and adjusted your plug gaps before installing them.
 
Plug gaps were a bit off but i adjusted em and went for a drive to see if the code would clear after another cycle but no luck. Gonna check the sensors this weekend if it doesn’t storm.
 
Plug gaps were a bit off but i adjusted em and went for a drive to see if the code would clear after another cycle but no luck. Gonna check the sensors this weekend if it doesn’t storm.
Did you figure out what was causing your po300?
 
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