You're describing two different problems. If the engine doesn't turn over, meaning it doesn't crank, that has nothing to do with fuel. It's a starter circuit issue. A real common problem is worn solenoid contacts that causes a single kind of loud clunk each time you turn the ignition switch to "crank". This always starts out as an intermittent problem. Troubleshooting must be done while the problem is occurring, or, the diagnosis is rather straight forward based on the symptoms.
If the engine turns over but won't start, that has nothing to do with the starter so troubleshooting it wouldn't make sense. The fuel pump could be failing to start up. Listen for its hum for one second after turning on the ignition switch. If you don't hear it, listen under the fuel tank or by the gas cap while a helper turns on the ignition switch. If you don't hear that one-second burst, suspect the fuel pump. That has nothing to do with the fuel quality. It has to do with mileage.
Caradiodoc
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Tuesday, January 11th, 2011 AT 7:44 AM