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Honda Repair/misfire 99 honda civic ex

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Question
what would cause a misfire shows code 301 302 303 304  399  and 420 i have changed plugs cap and botton  one fuel injector  and fuel filter when i unplug one of the injectors  it dont change

Answer
Since all of your cylinders are misfiring you need to look at things that will affect all the cylinders. You already replaced some of the tune up items but you didn't mention spark plug wires. I would change those first.
After that I would check fuel pressure and do a compression test. This will ensure that you are getting the right amount of fuel and that you have good compression. If the fuel pressure is low you likely have a fuel pump issue if the compression is low your engine is probably worn out internally.
These are the first things to check. You should find your problem in one of these items.

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Steve Porter

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I can answer most any common auto repair question. The only questions that I can't really answer are questions that would take lots of in-person time to diagnose.

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