How to Fix a Random Engine Misfire in Your Car (Code P0300)

One, two, three, four! Rev up your engines. [THEME MUSIC] It's time for scottykilmer.com. If your car's check engine light is coming on and if it has the dreaded PO300 code, today I'm going to show you how to fix random intermittent misfire codes in your car. The first thing you have to understand is that the misfires are random. It's not one cylinder. It has to be at least two or more, so start there. Start by checking the spark plugs. In this Toyota, take off the [? coil-on-plug ?] to get to the spark plug. Then put in a socket to take out the spark plug. Then remove all four spark plugs on this engine so you can check them all. If you find that all the spark plugs are way too worn and their gap has gotten too wide, replace all the spark plugs. That could fix your random intermittent misfire. But let's say your spark plugs are OK. Well, realize that it's multiple. So it's got to be something that affects the entire engine. So next, check for vacuum leaks. Check all the vacuum lines coming off the intake manifold, especially at the connections to see if the hoses are cracked and are sucking air. And in late-model cars, get some carburetor cleaner and spray all around the intake manifold. Because now they're made out of plastic and they'll often either get cracks or the gaskets will go bad. With the engine running, when you spray around the intake manifold, if it starts to change its idle, it means there's a leak and you need to fix it. Now, another thing that can cause random intermittent misfires is low fuel pressure. So get a fuel pressure gauge and open up your fuel injection system. If you have low fuel pressure, you could either have a bad pump or a bad fuel filter. So of course, change the fuel filter out first. They're cheaper and easier to do. Sometimes, a clogged-up fuel filter will cause low fuel pressure. And it's a lot cheaper than a $300 or $400 electric fuel pump. Now, the last common cause of intermittent misfires I'm talking about today is a bad battery. Everything in a modern car today is run electronically by computers. So have your battery checked with one of these machines. It only takes a minute. It just hooks up to each battery terminal. And then the test is begun. Here it goes. It's checking it, and it says "replace battery." Even though the battery is starting this car, it's not good enough to run it. So it's time to put a new battery in it. So if your check engine light is on with random intermittent misfire codes, now you know what to check. And remember, if you've got any car questions, just visit scottykilmer.com. And I'll answer them. [MUSIC PLAYING]

Channel: Scotty Kilmer

Views: 3,329,533

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Id: OyvdWeyDHf4

Length: 2min 56sec (176 seconds)

Published: Fri Feb 05 2010