Check engine light P0304 diagnostic code

1999 CHEVROLET 1500
148,000 MILES • 5.7L • V8 • 2WD • AUTOMATIC
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CHARLESTUCK
  • MEMBER
  • 66 POSTS
The check engine light is displayed. Occasionally, while driving, the light will come on for a brief period and go away for weeks. Sometimes for less. I have rearranged spark plug wires to make sure that they don't touch any metal. Then, I clear the code and that works sometimes. Other times, the check engine light comes on during long idle. Sometimes after the long idle, it goes away. Changing the spark plugs, wires, distributor cap, rotor, and air filter made no difference.
Mar 7, 2020 at 4:04 AM
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KASEKENNY
  • ✓Experienced Mechanic
  • 18,907 POSTS
We need to find out what the o2 sensor data is saying when the light turns on. At this point the most likely cause of this is a injector issue. However, looking at the o2 sensor data should help us figure that out.

If you don't have a scan tool that can read this data then we can always swap the injector for cylinder 4 with one on the opposite bank. This should tell us if the injector is the issue because the misfire will move to the cylinder that you put the injector on.

Let me know if you can get this data or what happens after you swap the injector. Thanks
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Mar 7, 2020 at 8:01 AM
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