P0300 after over rev
Thread Starter
Teching In
Joined: Aug 2017
Posts: 5
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From: Farmington NM
P0300 after over rev hello. I had an over rev going from 3rd gear to 2nd and when I hit I suppose the rev limit it bogged down and started a bad misfire causing my engine to shake bad going fast and P0300 code. I. Checked it out that night, #2 wasn’t firing but now it is, so I resolved that issue. Now I start it and it sounds great, idles just fine. I rev it to about 3-4K and when it comes down to an idle it misfires bad. And almost sounds like it is going to die. Then after awhile it picks back up. About 20 seconds after. I drove it out of my drive way last week and it bogged down and died. Took a while for it to start again and moved it back to my driveway. I replaced spark plugs and wires. I sprayed starting Fluid all around the engine bay and intake to hopefully pick up a leak. My fuel is at 55-60psi constantly. I am running out of ideas. I don’t hear anything internally, my pushrods are not bent, I only checked #2 cyl. If it is electronic what would it be? I can start it right now and idle alright. Soon at I hit about 3-4 grand it starts the multi misfire. Only code existing is EGR valve bad cause I did headers and ORY. Would that effect it? If there is a bad sensor should a code show??
Thread Starter
Teching In
Joined: Aug 2017
Posts: 5
Likes: 0
From: Farmington NM
Holy smokes. I overlooked the valve springs and found #2 cyl was broken. Now time to go replace it. I wonder why it didn’t just throw a code for #2 and only a misfire. Soon as I replace it I’ll upload my results on it. Thanks RockinWs6
Because if it doesn't meet the misfire threshold it won't kick a cylinder specific misfire code. It runs the misfire test for a certain amount of time in different conditions. If the threshold is 4000 misfires within a certain time limit, if it misses 3999 times, it won't kick a specific cylinder misfire and will give you the P0300.
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Joined: Mar 2013
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Because if it doesn't meet the misfire threshold it won't kick a cylinder specific misfire code. It runs the misfire test for a certain amount of time in different conditions. If the threshold is 4000 misfires within a certain time limit, if it misses 3999 times, it won't kick a specific cylinder misfire and will give you the P0300.
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I would replace the springs that are broken first. I would then leak down that cylinder. Hopefully you didn’t bend a valve, but now is the time to check.
If the cylinder in question specs out ok I would then replace all the springs and then do a leak down check on those cylinders. I would also check all the pushrods on a super flat surface to ensure they are still straight.
Not saying you hurt a valve but while you have it down this far you would be smart to check it.
If the cylinder in question specs out ok I would then replace all the springs and then do a leak down check on those cylinders. I would also check all the pushrods on a super flat surface to ensure they are still straight.
Not saying you hurt a valve but while you have it down this far you would be smart to check it.
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