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Q: Misfire wont go away

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Problem started with misfire codes on cylinder 8, then cylinder 5, then random misfire. Did full tune up, replaced iac, cleaned fuel tank, changed fuel pump and filter, had vaccuum and compression test done. Checked cat and oxygen sensors. Replaced injectors with 4 hole 21lbs, cleaned fuel rail, ran great for 130 miles. Now is even worse, stumbles, no engine light but stored codes say random misfire, plus misfire on all 8 cylinders. At a loss on what to check next.

My car has 188000 miles.
My car has an automatic transmission.

Hi there. From your description of all that has been done. I suspect you may have a computer problem. The powertrain control module (PCM) is designed to store a fault code in pending codes, on the first drive cycle that it recognizes a malfunction. If, on the second drive cycle, the PCM recognizes the same malfunction, the check engine light should come on and stay illuminated. The check engine light typically flashes during misfires detected. This may also be a connection problem at the PCM. Programming may also be an issue. Try disconnecting the negative terminal of the battery. Disconnect and inspect the electrical connector(s) at the PCM for signs of corrosion or loose terminals. Repair as necessary. Reattach connector(s) and reconnect negative battery terminal. The computer will have a period of relearn, idle speed, etc. This should happen with a short road test. Something else to look at would be the ignition coil(s) output. If you are unable to resolve the misfire(s), a certified YourMechanic technician can come to your location and perform an engine misfire inspection on your vehicle to help diagnose this issue and suggest any service needed.

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