Intermittent no start issue

You could be correct if the pump is the issue. Did they test it when it was not starting or was it starting when they tested it? If you are losing pressure intermittently then we clearly need to test it when it is acting up.

There are a number of other things that can cause this so the key thing is to do all testing when this is not starting.

When it is not starting, does the engine turn over and not start or does it not do anything when you turn the key.

If it is cranking, when it does it next time try spraying some starting fluid in the intake and see if it fires. If it does then it is fuel related and we can go down that path.

https://www.2carpros.com/articles/car-cranks-but-wont-start

The other major cause is a crank sensor. Clearly we need to test this before just replacing it but let's start with fuel.

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

How often does this do the issue where it doesn't start? If we can get it to do it again, we need to remove a spark plug and check for spark. If we have spark then we can go back to fuel. Were you able to confirm it was a fuel issue prior to putting the pump in it? When it was doing it did you spray some starter fluid in the intake?

Basically we need to find out if this is a fuel issue or ignition issue. Thanks

If it is the ignition system we need to start with if there are or were any codes. Then we need to monitor the signal from the crank sensor that the ECM is seeing. If there is no crank signal then it will not start or run because the ECM will not know where the engine position is. This is where we need to start because it is the most common cause of a no start that is not fuel related. Clearly we need to do all this testing when it acts up.

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor