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OBD code P0304 Question

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Old 07-11-2010, 06:22 PM   #1
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OBD code P0304 Question

My 2003 Tacoma 4 cylinder 5 speed SR5 has developed a "misfire" in cylinder #4 (code P0304) that comes and goes. The strange thing is that the mis starts after a hot restart and usually clears up after driving it for a while. I changed the plugs (which looked fairly good) but the problem continues. Has anyone seen a similar problem?
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Old 07-11-2010, 06:26 PM   #2
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Welcome to TW!

Most common cause is a bad coil, wire, or fuel injector. Make sure the wires are connected propperly. Test the #4 wires, and see if they are good. Then, you may want to swap injectors, and see if the issue moves to the new cyl.
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Old 07-12-2010, 09:45 AM   #4
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If you have scan data while the engine is missing.............

Look to see if it is in "closed loop fuel control". If so, look at the fuel trims during the misfire. If it is adding fuel less than 15% start with ignition check out. If it is adding fuel at about 20% look at an injector issue.

If the fuel trims are negative, it could be a leaking injector or fuel pressure regulator. A leaking fuel system component tends to show up more on a hot restart due to a fouled plug before the fuel has had a chance to evaporate while sitting for some time.

Just rules of thumb to go with the above good posts. Nothing beats methodical checkout.
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Old 07-13-2010, 09:41 PM   #5
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I want to thank those who responded to my question for their help and the welcome from Chris. I switched 2 coils and nothing changed so I ruled out a spark problem. Next I used a sound scope to listen to the injectors as the Toyota manual suggested. Number 4 sounded much quiter with a different frequency so I measured the injector resistance and found an open circuit. I ordered a new injector and gaskets/O rings and hope to complete the repair soon.

John
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