97 Ford F150 4.2 Fuel Pump Primes but won't start.

Unless the pump is loosing pressure somewhere in lines ect. All is o.k. Pump only runs when it needs to keep pressure up. Only takes a few seconds at start up. The 4.2l has a throttle body and also a fuel injector at each cylinder delivering fuel. The throttle body persay is a air body no fuel here. There is a sensor in the throttle body telling the computer how far the throttle is open and behind that on top of the intake is the IAC and in the air filter tube just up from the filter toward the intake is the MAF if these are dirty or bad it can cause the injectors to not get the signal to open. Those parts I just list are Big $$$$. I would do for way less dollars just to be sure or rule out those. Clean them with Contact cleaner or MAS cleaner for the MAF and Throttle Body Cleaner for the throttle Body & IAC and new gaskets on the throttle body & IAC. There are some test you can perform to find out if they are bad or working and if they fail it could be dirty instead of bad thats why I say clean them first and if that does not fix it then test with a volt meter. Do not touch the MAF sensor just spray it. I will say this most times it just runs bad if these fail but since you checked all the relays. I am sure they are dirty by now being a 97. otherwise it may be a CPU issue maybe a fuse something is not working or the injectors would open. I have a book for this model I will see it says anything else and get back if it does.