My Turn! P0301 Misfire Cylinder 1 (Resolved for real this time)

[Endlessblockades]

I'm going to do a wire/plug/pack inspection tomorrow, but after reading a bunch of threads, I'm hoping I have an injector problem. I'm positive they are the original units. Runs fine from cold start, stumbles on a warm start. I watched Timmy and Sean's video and YOLO'd on a full set of the Denso reman injectors, fuel rail crush washers, and gaskets from MotorWest Performance. Not even sure that's the problem but that's how I roll, unfortunately. Doing one is enough of a PITA so, why not? I will move the coil pack but I doubt that's it. CEL is on but not flashing so I can limp it around to stay ahead of the streetsweepers, right?

 

[mtbtim]

Like you mentioned, your first step should definitely be to swap the coil packs. Swap the #1 and #3 coil packs and see if the misfire moves to the #3 cylinder. This will confirm or rule out a coil pack problem.

If the misfire stays at the #1 cylinder, you can pull the spark plug and take a look. If the electrode looks worn, you may as well replace all 6 spark plugs because they are due. While you have the spark plugs out, this would be the opportune time to do a compression test to check the health of all your cylinders. Sean and I have a video for that as well.

If the new spark plug does nothing, then I'd look into replacing the fuel injectors using our video.

Good luck!

 

[Endlessblockades]

Like you mentioned, your first step should definitely be to swap the coil packs. Swap the #1 and #3 coil packs and see if the misfire moves to the #3 cylinder. This will confirm or rule out a coil pack problem.

If the misfire stays at the #1 cylinder, you can pull the spark plug and take a look. If the electrode looks worn, you may as well replace all 6 spark plugs because they are due. While you have the spark plugs out, this would be the opportune time to do a compression test to check the health of all your cylinders. Sean and I have a video for that as well.

If the new spark plug does nothing, then I'd look into replacing the fuel injectors using our video.

Good luck!

Thank you - that is exactly my plan! I went ahead on the injector set while secretly hoping I don't need then (yet). Do you happen to know why a hot vs cold engine affects the misfire? I have barely driven 3 blocks since the misfire began, but is seems to only happen on a warm restart. Thank you guys for your support and videos.

 

[alumarine]

Thank you - that is exactly my plan! I went ahead on the injector set while secretly hoping I don't need then (yet). Do you happen to know why a hot vs cold engine affects the misfire? I have barely driven 3 blocks since the misfire began, but is seems to only happen on a warm restart. Thank you guys for your support and videos.

A bad coil might only act up when it's hot.
Could be other things as well.

 

[Endlessblockades]

A bad coil might only act up when it's hot.
Could be other things as well.

It's the other things that worry me - but, onward......

 

[Endlessblockades]

So given the lack of time yesterday I got as far as swapping coil pack in cylinder 1 with 5 (meant to do #3 but a nasty cold / brain fog is my excuse - first one since well pre-covid). I didn't realize I didn't have a 5/8 socket, so I couldn't pull the #1 plug. The reason I'm even mentioning this half-assed progress it to mention that the seat for the #4 cylinder (on the #1 coil pack) was full of crusty dust and the metal pin was encrusted with turqouise, uh oxidation?. The other 2 on the passenger side did not have that. Unfortunately, I cleaned and blew it out for the most part before I took the photos below, so keep in mind it was way worse looking than the other two. The #4 cylinder didn't seem affected, but I am wondering if that may point to an issue with the coil pack that was sitting on #1 or some resistance somewhere else?. Hoping the misfire issue moves to #5 or #2. While I was moving the intake out of the way I did clean the MAF - the wire was filthy. I cleaned it last a couple of years ago..... thanks for any insight. Will check plugs next before investing in a compression test kit.

P.S. I'm using an OEM air filter but have been to the desert several times.

 

[Endlessblockades]

After swapping packs, I now get a PC of 0300. Should I wait until it goes full TC/CEL (will it ever pinpoint a cylinder?), or is the new Random Misfire code enough to lean towards coil packs? I got the new code within less that a mile of driving after a couple warm starts. Give it some more time to collect data? God I hope it's just a coil pack. I need to go camping at a bike race in less than 2 weeks.

If it turns out to be that, I will do 6 plugs since I'll have the slightly more involved side exposed anyway. Am I being too hopeful here without further testing?

 

[phattyduck]

. While I was moving the intake out of the way I did clean the MAF - the wire was filthy. I cleaned it last a couple of years ago.....

The picture you show there is just of the temperature sensor. If that's dirty, it doesn't matter much. The wire that matters is down inside the venturi tube.

-Charlie

 

[Endlessblockades]

The picture you show there is just of the temperature sensor. If that's dirty, it doesn't matter much. The wire that matters is down inside the venturi tube.

-Charlie

Yes, I drenched the innards with MAF cleaner as well. I didn't realize the exposed wire was only for temp, though - thank you.

 

[Endlessblockades]

Update. New coil packs and wires has it running beautifully. I'll shelve the injectors for the distant future...

 

[Dizzle801]

I've been getting a P0302 misfire but only when going up hill or up a mountain pass. I live in Utah and mountain bike but this misfire has kept me for going to some favorite spots. Ive replaced plugs, wires and even replaced one of my coils (All from my local Toyota dealership). Still getting the same CEL that blinks when I attempt to go up a mountain pass. Around town its just fine and never an issue. Compression tested fine and numbers are consistent and well within range. Fuel filter was replaced about 6k miles ago. could this be a fuel injector? still a newb on the forums so i have to piggy back on this thread since its CEL related.

 

[Endlessblockades]

I've been getting a P0302 misfire but only when going up hill or up a mountain pass. I live in Utah and mountain bike but this misfire has kept me for going to some favorite spots. Ive replaced plugs, wires and even replaced one of my coils (All from my local Toyota dealership). Still getting the same CEL that blinks when I attempt to go up a mountain pass. Around town its just fine and never an issue. Compression tested fine and numbers are consistent and well within range. Fuel filter was replaced about 6k miles ago. could this be a fuel injector? still a newb on the forums so i have to piggy back on this thread since its CEL related.

I wish I had some advice but I'm not a mechanic, just a parts-swapper unfortunately. My issue was only on a warm restart and somewhat intermittent. I could have sworn I felt a stumble the other day driving back and forth to the Sea Otter. That was after posting that this issue was Resolved and now my OBDII is constantly set to monitor Pending Trouble codes (pre-CEL). It's kinda annoying waiting for failure. When you get the CEL, does it run rough? The coil pack on Cyl 5 sends the spark to Cyl. 2. Have you tried swapping that pack with another to see if the cylinder misfire code changes?

 

[Dizzle801]

Yeah, the first time i got the CEL I swapped the coil to see if it would happen again. I was hoping the misfire would jump and it would just be replacing another coil. Since the misfire remains the same cylinder 2, i think my next job is going to be replacing the injectors. Seems more reasonable to replace all of them since ill have it all exposed anyways and shes got 290k on the clock.

 

[19963.4lsr5]

Yeah, the first time i got the CEL I swapped the coil to see if it would happen again. I was hoping the misfire would jump and it would just be replacing another coil. Since the misfire remains the same cylinder 2, i think my next job is going to be replacing the injectors. Seems more reasonable to replace all of them since ill have it all exposed anyways and shes got 290k on the clock.

Did you try something as simple as some premium injector cleaner? If it is possible it’s a dirty injector…


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[19963.4lsr5]

I wish I had some advice but I'm not a mechanic, just a parts-swapper unfortunately. My issue was only on a warm restart and somewhat intermittent. I could have sworn I felt a stumble the other day driving back and forth to the Sea Otter. That was after posting that this issue was Resolved and now my OBDII is constantly set to monitor Pending Trouble codes (pre-CEL). It's kinda annoying waiting for failure. When you get the CEL, does it run rough? The coil pack on Cyl 5 sends the spark to Cyl. 2. Have you tried swapping that pack with another to see if the cylinder misfire code changes?

Toyota’s missfire code leaves a lot to be desired, at least on the 96-98 ECU.

I had a bad coil on the 97 limited. Engine running ruff, shaking at idle, reduced power etc. ex wife told me about it after she got home. Drove it 20 miles like that. I looked stuff over and then drove it out to my bigger shop at her mom’s house to look at some more things. As I was turning into the driveway 3miles later the check engine light finally came in and started flashing. missfire code present and I had a bad aftermarket coil.

The 96 did the same thing when it had a bad coil.


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[Dizzle801]

I havent tried a fuel injector cleaner in a bit but ran them about every other tank for a while. I also only use premium in it. Probably a bit overkill but figure shes worth it.

 

[Endlessblockades]

So, after I said my warm misfire was Resolved, it came right back (of course it did!) and I didn't want to post another message until it really was. Yes, it was an injector. I did all 6 so I don't know if it was only the one that most frequently threw a code - others did occasionally, too, and I also got a p0300 Random code from time to time. The path to this resolution was longer and more expensive than it should have been because I tried everything 'easier'. I'm guilty of hoping for a simple solution - human nature. If I was a mechanic I would have used a more logical approach. Maybe being a computer mechanic for a couple decades clouded my mind because hardware and software are controlled by black magic sometimes and you have to try all kinds of approaches and there in no FSM. The thing now runs really really well and feels more responsive and punchy. As a result of meandering to the conclusion, I learned that I have rather good & uniform compression in all cylinders and I own a compression tester now. I ended up with new plugs, wires, coil packs, and a junkyard Igniter. As others here had said, a misfire on warm restart is probably/nearly always injector-related. Live and learn. Thanks to Timmy and Sean's injector video!!