90 Ford Ranger 2.9l engine?

Won't start, got gas to schrader valve, got spark to plugs but will not start unless I put gas in the throttle body then it will pop off but won't stay running

Maybe you should hook a pressure gauge to that Schroeder valve this time.

Has gas releasing from the Schrader valve does not mean that you have good gas or enough pressure for the engine to run. Check for contaminated gas and make sure the system has good pressure. The fuel pressure on the 2.9L should be 35-45 Psi.

Now back firing is another matter. Recheck the timing. Start with the vacuum reading, fuel reading, compression reading, check the timing and go from there. Ignition timing is 10 degrees BTDC @ 800-850 rpm for both AT ot MT.

Bad injectors. Injectors not getting command to fire.
Vacuum leaks.