From what you've done so far, sounds like a computerized ignition problem, unless you're timing chain went out. The only things that would prevent spark to you're plugs would be if you're Oil Pressure Sensor is bad or a faulty/dirty R.P.M sensor.
Need more info, does it turn over? Did you check to see if you have fuel getting to the engine (does the pump in the tank run when you turn the key)? Do you have spark (check with a inline spark tester $6.00)?
To pressure test a radiator cap, you will need a radiator pressure tester kit. Remove the radiator cap, attach the pressure tester to the radiator neck, and pump it up to the specified pressure level. Observe for any leaks or pressure loss to determine if the radiator cap is functioning properly.
The starter or solenoid are most likely bad. The starter assembly can be removed and put on a starter tester to see if its bad.
Sears
A dead weight tester is an accurate calibration source of pressure. A dead weight tester uses weight over a precisely known area to produce an accurate output pressure. Uses would be precision calibration of gauges, transmitters, switches and level devices.
When selecting a natural gas pressure tester, key features to consider include accuracy, pressure range, durability, ease of use, and compatibility with different types of natural gas systems.
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To hook up a vacuum, pressure, and tester on a 2002 Saturn L300, first locate the intake manifold vacuum source; typically, you can use a vacuum port on the manifold. Connect the vacuum gauge to this port, ensuring a secure fit. For pressure testing, disconnect the vacuum line and connect the pressure tester to the same port. If you're testing for leaks or other diagnostics, follow the manufacturer's instructions for the specific tester you are using.
That is a sound pressure level meter (SPL meter).
thats a little on the worn engine side of compression,but that in itself would not keep it from starting....most likely a fuel or spark problem. you can check fuel pressure with a screw in guage from autozone,and check spark with an inline spark tester from autozone.
A gas line pressure tester is used to check for leaks and ensure that gas lines are operating at the correct pressure. By pressurizing the line and monitoring for any drops in pressure, the tester can identify leaks that could pose safety hazards or reduce the efficiency of the system. This helps to prevent gas leaks, potential explosions, and ensures that the gas system is working properly.
get a fuel pressure tester on the fuel line going to throudle body there is a fitting looks like a valve stem twist off cap screw on the tester . hold tester so you can see it and turn key but dont start the motor if it reads below 54 pounds its bad. check with auto store on pressure to be sure im close.