Engine turns over but will not start

Hi and thanks for using 2CarPros.com. Since the problem is erratic, you will have to check for spark and fuel when it refuses to start. One will be missing.

Here are general directions for checking for fuel:
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Here are general directions for checking spark:

https://www.2carpros.com/articles/how-to-test-an-ignition-system

Here is a general overview of a no start situation:
https://www.2carpros.com/articles/car-cranks-but-wont-start

The fuel pump pressure specific to your vehicle is:
Ignition ON Engine OFF 62-90 kPa (9-13 psi)

Here are test instructions specific to your vehicle:

TESTING AND INSPECTION
PROCEDURE:
Turn engine "OFF" and relieve system pressure.
Plug THERMAC vacuum port on TBI.
Uncouple fuel supply flexible hose in engine compartment. Install fuel pressure gauge between steel line and flexible hose.
Tighten gauge in line to insure no leaks occur during testing.
"START" engine and observe fuel pressure reading. It should be 62-90 kPa (9-13 psi).
Gradually restrict (pinch) outlet side of gauge. Fuel pressure should rise to 90 to 103 kPa (13 to 15 psi). This checks maximum pressure (dead head pressure) and determines if high fuel pressure is due to a restricted fuel return line or a TBI pressure regulator problem.
Relieve fuel pressure remove fuel pressure gauge.
Reinstall fuel line.
"START" engine and check for fuel leaks.
Remove plug from vacuum port and install air cleaner assembly with new gasket.

Let me know which one is the problem so I can better help.

Take care,
Joe