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Q: Vehicle misfiring and I don't know why

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It feels like my vehicle engine is misfiring, but the Check Engine light is not coming on. The RPMs also jump up and down. I have changed the fuel pump, fuel filter, spark plugs, plug wires PVC valve, and run a fuel additive called HEET through it. I also changed the thermostat for an unrelated problem, and inspected the fuel rail. I do not know what to do next and need professional help.

Hi there. The ignition system on this engine includes the distributor, cap and rotor. The distributor is a common issue on this engine due to failure of the sensor inside of it. The sensor will cause an erratic RPM signal and cause the misfire you are experiencing. If the distributor is the source of the problem, it is recommended to have the distributor changed along with the cap and rotor. Have a certified mechanic replace the bad distributor to eliminate any further complications with your vehicle.

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