Q: My 98 gmc safari van will turn over but won't start replaced the starter and still doing it what can it be

Confirm that the engine immobilizer system (security system) is not activated thus preventing the car from starting. If the immobilizer system is on, you may see a security warning light. If the warning light is on, to temporarily override the immobilizer system, see these instructions. If the engine cranks at adequate RPM, be sure there is adequate fuel in the fuel tank and that the fuel is not old. Download any OBD-II trouble codes that have been stored and examine those codes for diagnostic clues. Check for adequate fuel pressure, injector operation, and a spark at the spark plugs. Basically, if the starter motor is turning the engine over rapidly, at sufficient RPM, but the engine does not catch and run, that means that there is an ignition, fuel, air induction, or mechanical fault in the engine that will have to be repaired. Check for vacuum leaks, an air induction fault like a stuck idle air control valve or, considering fuel, check for a failed temperature sensor that must be working properly to signal the PCM to enrich the mixture on cold start. Other possible no start faults are low compression, defective spark plugs, a defective coil(s), a failed crankshaft or camshaft position sensor, a failed throttle position sensor, and a broken timing belt/chain. Regardless of the underlying cause, if you request a no start diagnostic the responding certified mechanic will get the problem diagnosed and repaired for you promptly. Please let us know if you have further concerns or questions as we are always here to help you.