Misfire codes P0420 and P0302?

2007 TOYOTA COROLLA

117,000 MILES • 4 CYL • AUTOMATIC

DQ671

MEMBER
20 POSTS
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Been getting misfires recently. First started with a P0302. Then changed out all spark plugs and coil packs, then one day accelerated and went faster and then misfire came back but this time with P0420 catalyst. Again I swapped out all plugs again ran good but as I was going up hill I got a misfire again cylinder 2 . So at this point just reaching out for some expert advice as to what might be causing these misfires or every time I go over 50 miles per hour it’ll misfire, and performance is sputtering . Thanks in advance, maybe y’all can point me in a direction to check next. Thank you

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Jun 1, 2025 at 3:12 AM

STRAILER

CERTIFIED EXPERT
53,856 POSTS

When you pull the spark plug out of #2 cylinder does it look dark, or black compared to the others? If so, it sounds like the fuel injector needs to be replaced, here is how to remove the fuel rail to swap it out. Here is how to test the injector once it is removed:

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Check out the images (below). Let us know how it goes.

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Jun 1, 2025 at 10:58 AM

DQ671

MEMBER
20 POSTS

They all look pretty much the same greyish dark. But I’m going to check out the injectors next like your advice hopefully that solves it otherwise I’ll continue to learn as I go. Thank you I’ll update once I find the issue.

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Jun 2, 2025 at 2:25 AM

STRAILER

CERTIFIED EXPERT
53,856 POSTS

Sounds good, I am here to help. Yep, the injector will be the next step. Does the engine run smoothly? If not, you might want to do a compression test on #2. here is a guide:

https://www.2carpros.com/articles/how-to-test-engine-compression

You can rent a gauge set at the auto parts store for free. Please go over this guide and get back to us.

Jun 2, 2025 at 11:35 AM