New Codes: P0300 and P0301

[DWilliam]

2002 SR5. Recently at the mechanic for a new fuel pump and overflow check valve to try addressing evap codes. I'm unsure how long these current codes have been there, as I let the CEL stay on for the past couple months while I waited on parts.

Codes:
P0300; Random/Multiple Cylinder Misfire Detected
P0301; Cylinder 1 Misfire Detected

Symptoms:
Nothing major. Every once in a while when I fill up the tank it will take a few extra seconds to start, however I assumed this was from an old fuel pump, which has been replaced.

Should I start with new plugs and wires? If so, is that an easy job, or should I let my mechanic take care of it? I've done pugs before, but not wires and not on a 4runner.

Anything else I should address?

 

[Bad Luck]

2002 SR5. Recently at the mechanic for a new fuel pump and overflow check valve to try addressing evap codes. I'm unsure how long these current codes have been there, as I let the CEL stay on for the past couple months while I waited on parts.

Codes:
P0300; Random/Multiple Cylinder Misfire Detected
P0301; Cylinder 1 Misfire Detected

Symptoms:
Nothing major. Every once in a while when I fill up the tank it will take a few extra seconds to start, however I assumed this was from an old fuel pump, which has been replaced.

Should I start with new plugs and wires? If so, is that an easy job, or should I let my mechanic take care of it? I've done pugs before, but not wires and not on a 4runner.

Anything else I should address?

I would start with plugs and wires, and switching the coil pack for #1 with a different one to see if it follows that. Plugs and wires aren't bad with the right tools. Take your time with the plug wires and look for a plug wire routing diagram when you do it. They're quite easy to switch around and you'll end up with more misfires.

 

[98&me]

I would first check the spark plug for any strangeness. Then I personally would check the compression. ( I got the 300 code and 306 code which turned out to be a stuck exhaust valve)Then I would swap coils with a known good one. Clear the codes then do the code reset procedure.

 

[DWilliam]

Thanks for the replies. I ordered plugs, wires, and MAF cleaner. Watched a couple youtube videos and it seems pretty user friendly. Anything else I should look out for when I'm doing the job?

 

[Bad Luck]

Thanks for the replies. I ordered plugs, wires, and MAF cleaner. Watched a couple youtube videos and it seems pretty user friendly. Anything else I should look out for when I'm doing the job?

Check the boots on the coil packs for any signs of cracking/tearing. I'd also keep track of what spark plug came from where so you can reference it later.

 

[DWilliam]

If the misfire is on clylinder 1 per the code, is that injector relatively easy to replace? Should I test the coil pack first? And if so, is a coil pack difficult to replace?

 

[Devbot]

If the misfire is on clylinder 1 per the code, is that injector relatively easy to replace? Should I test the coil pack first? And if so, is a cool pack difficult to replace?

Much easier than the driver side, I think you should be able to take off the fuel rail with just the throttle body removed and don't need to take off the entire intake? I just replaced an injector today on the passenger side and it took me about 90 minutes all said and done, so for the driver side I would expect half that at the very most.
As already mentioned, your first step should be moving the coil pack to another cylinder to see if the miss follows.
You can also test the injector with a multimeter, they should read between 13-18ohms (my MotorWest injectors read 13.5 across the board, but when I tested my OEM brown ones last year they were all near 17). If the problem is a dead injector, it'd be a good idea to pick up new crush washers for the fuel rail (#90430-12026, you need two for each banjo bolt.)

Have you been driving the vehicle since making this thread? Given that it seems like you're just starting to address the issue and it's been about a month since the original post, then it would be very wise to change the oil if you find the problem is just the coil pack and not the injector itself, as it's probably very laden with gasoline. Oil can take a little bit of gas and burn it off, but a ton of it is a good way to blow a hole in the side of the block.
You also mention you didn't notice the codes were there, and had no major symptoms. Did you ever try clearing the code and seeing if it came back as 98&me suggested? You would know right away if you had a constant misfire. It would run like hell and the CEL would be flashing.

 

[DWilliam]

Thanks for the reply. I have been driving it, but with a solid CEL, no blinking. Seems to run fine. I’m planning on doing plugs, wires, 1 coil, and clean MAF sensor this weekend and see if that helps.

Much easier than the driver side, I think you should be able to take off the fuel rail with just the throttle body removed and don't need to take off the entire intake? I just replaced an injector today on the passenger side and it took me about 90 minutes all said and done, so for the driver side I would expect half that at the very most.
As already mentioned, your first step should be moving the coil pack to another cylinder to see if the miss follows.
You can also test the injector with a multimeter, they should read between 13-18ohms (my MotorWest injectors read 13.5 across the board, but when I tested my OEM brown ones last year they were all near 17). If the problem is a dead injector, it'd be a good idea to pick up new crush washers for the fuel rail (#90430-12026, you need two for each banjo bolt.)

Have you been driving the vehicle since making this thread? Given that it seems like you're just starting to address the issue and it's been about a month since the original post, then it would be very wise to change the oil if you find the problem is just the coil pack and not the injector itself, as it's probably very laden with gasoline. Oil can take a little bit of gas and burn it off, but a ton of it is a good way to blow a hole in the side of the block.
You also mention you didn't notice the codes were there, and had no major symptoms. Did you ever try clearing the code and seeing if it came back as 98&me suggested? You would know right away if you had a constant misfire. It would run like hell and the CEL would be flashing.