Engine wont start.

If your 1991 Chevy's 4.3 Vortec engine has spark and fuel, but still fails to ignite, there are several possible reasons to consider. Timing: Make sure the burn time is set correctly. Incorrect timing can prevent the engine from starting. Double-check the timing marks to make sure they align properly. Compression: Make sure the engine has adequate compression. If the pressure is low in one or more cylinders, starting problems may occur. A compression test will help determine this. Fuel Delivery: Even though you said it has gas, pay close attention to the fuel delivery system. Make sure the fuel pump is working properly, the fuel filter is clean, and the fuel lines are not clogged or leaking. Air intake: Inspect air intake for blockages or leaks. A clogged air filter or leaking intake manifold gasket can affect engine performance. Vacuum leaks: Check the vacuum lines and connections for leaks. A vacuum leak can cause an uneven mixture of air and fuel and cause starting problems. Sensors: The engine relies on sensors to send information to the computer unit (ECU). Defective sensors such as the crankshaft position sensor or camshaft position sensor can prevent the engine from stalling. Wiring and connections: Ensure all electrical connections are secure and non-corrosive. Damaged wiring or loose connections can block signals to engine parts. ECU/PCM: The engine's computer (ECU/PCM) can be faulty, preventing proper signals from reaching the engine components. Distributor cap and rotor: If your engine uses a distributor, inspect the distributor cap and rotor for any signs of wear or damage.

What make vehicle ? year an model too ! Before you replaced those parts did you check for battery supply voltage an check the ground for those components ? You need to get a wiring diagram an see what get's voltage an what is ground ! An see what all is involved , crankshaft position sensor , ECM / PCM -engine computer etc...! Then you need a DVOM - digital volt ohm meter to test ! Your looking for a quick fix an doesn't work like that !

firs thing is chek for fuel and spark add some crb cleaner while cranking si ifthe engine attempt to star you may have to address a fuel problem listen for humming noise coming from trunk area when key is turned to run position this indicates if fuel pump is running from here you will need a fuel pressure gauge to hooked and check for the rit fuel presuure 30 psi good luck

code p0341 refers to cam shaft position sensor(CMP)sensor A bank1---range/performance problem===causes--insecure sensor/ rotor---air gap---wiring---CMP sensor.. I would pay attention to the sensor and the possible causes as listed because the timing of the engine is related to the position of the cam shaft. Timing is computer controlled and will not be "off" unless the CPU cannot get a definite position of the piston to set the timing

run the fault codes and check for cam/crank position sensor . check that the cam shaft is turning (broken cam belt)

Code 12 is a "good" code-it means system normal.
Since no codes are stored, check for spark and check for gas-is the fuel pump coming on? You should hear the pump buzz for a couple of seconds when you turn the key to on-it should start and pressurize the lines, then shut off until the engine is cranked-when cranking, pump should be running again. If you don't hear the pump, check if the fuel pump wire at the gas tank connector has power to it when the engine is cranking. If it does and the pump is not working, the pump will need replacing.
If no power, check the fuel pump fuse and relay, under the hood.
If the fuel pump is working, it may be ignition related-check for spark. You need to see a blue snapping spark to know the ignition system is good. If no spark, suspect the ignition control module or the crank position sensor -or the pickup coil, if no crank sensor. The pickup coil will be in the distributor-if you have one. If no distributor, crank position sensor is behind the crankshaft harmonic balancer.
If fuel pump and spark are good, you will need to diagnose the injector circuit.
Post back with what you find.

Pull off the coil ignition cable at the distributor and check for spark coming out of coil when cranking engine over. Use a heavy rag or glove to hold the wire 1/4 inch from a metal ground. Should see a strong blue spark when cranking to verify ignition is good. If no spark, check for battery voltage to coil on the coil primary. If you have current to the coil, suspect a bad coil, ignition module, crank position sensor, or cam position sensor, or pcm. The coil, ignition module, and sensors can be tested before replacing.

Chek for Fuel Filter and Pump.... Vacumm lost. and Idle sensor for contact lost during engine run Possibility gas line interuption
due to Fuel Pompe Damage

Try squirting some starting fluid in the intake and see if it starts if it starts then dies its lacking fuel this could could be that the crank position sensor could be bad. Do you have any codes and have you had them extracted( check engine light is on).the fuel pump may be working and you may be getting fuel up to the fuel rail but if the injectors are not getting the signal to pulsate you will not get any fuel in the intake so check the crank position sensor.Try this first if this doesnt do it check the timing how many miles are on the vehicle if it has high milage it may be in the timing belt. If this has helped you please rate my assistance towards you thank you.

ck the crank position sensor. It's on the front of ehgine at the crank pully. If there seems to be a fuel problem, ck the maf sensor. first sensor out of air cleaner. good luck