Q: the starter issue on 1990 Jeep Cherokee

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i have replaced the starter 3 due to something i thought it was the battery and that was not it i replaced that before the starter but i thought it was the alternator they say no so why does the starter keep going out if every thing else is good i also have had gas issue i replace the filter and gasoline to valareo and it works better but i needs alot of advise on this truck where do i go what i do
(1) Answer
If you are not getting factory quality parts, they can keep failing at a very fast rate. When the Jeep does not start, does that battery still have at least 12.6 volts? The headlights working is not a sufficient test, you need to measure the voltage. Does the Alternator put out at least 13.8-14.1 volts when the Jeep is idling with all electrical loads off, i.e. the lights, wipers, heater etc.