91 5.0 won't start
 

I'm hoping for a little direction for my 91 LX 5.0 that won't start. I have had no issues with the car until one day it had a hard time starting. After driving if for about 15 minutes I got gas and it wouldn't start at the station. I had it towed home. The next day it started with no issue but the next time I tried to it wouldn't.

I replaced the fuel pump relay and ignition switch as they were easy and inexpensive but with no success.

The fuel pump would sometime come on after turning the key but wouldn't pressure up and now is not coming on at all.

I have read it could the fuel pump, the regulator, the PIP or TIF, and possibly the ECU.

With this symptoms, can anyone give me the best place to start? Any help would be appreciated.

I would start with the fuel pump most likely of all the possible suspects, but I did notice you didn't check the filter either.

The fuel filter has less than 5-6k miles but is 2-3 years old. I plan on replacing it in the next day or two as well.

First, find out what's missing when it won't start. Fuel or spark ? Then you can narrow it down from there.

Get your test light or voltmeter to see if the pump is getting power. I'd be leaning towards the pump since it quit after refuel. How low was your tank before refill? A pump on its way out often fails after a fill up. Fuel is the coolant for in tank pumps and if it's been run below 1/8 tank regularly then it's been overheating. The cool fuel hitting a hot pump often seizes it up.

Update
 

Ok. I have replaced the fuel filter and checked the fuel pressure. The pump starts up when the key is on but does not stop within the 5-20 seconds. The fuel pressure was steady at 38-39 psi and went down slowly while cranking. Does it sound like the fuel pump and regulator are ok? I had too many fumes to test the spark at the same time.

Any suggestions?