Engine will not start up?

I am having a problem starting my vehicle after it has set for a time. The things I have done fuel pressure with Key on Engine off 35psi key on engine running 30psi. I have check for fuel available after it sits and fuel is present at the rail on the injectors. Switched reelays around to see if any difference and there is not. I have checked and ignition fire is present.

I have replaced both the EEC Relay and the fuel pump relays. I have also tried starting fluid and it does not help. Check engine light is not on as I continually crank it will backfire and eventually start and run very rough until the temp comes up then it runs fine and will start fine until it is allowed to sit and cool off.

It does

I have to say I am disappointed in the slow or no response.

For about 4-5 months my Ford Explorer would sporadically turn off, but would turn on again after a good 15-20 minute cool down. Just recently, the car turned off and wouldnt' start up again at all.

I had the fuel pump replaced, but that didn't help.

I tested to see if the fuel pump engaged, and it did, but when I test to see if fuel will squirt out of that test valve on the engine (not sure what its called), very little pressure comes out, and this was the case the whole time I had this car ( I bought it used ).

Recently, i've had suspicion that it would be the Crank shaft position sensor?

Any opinions?

Also, i'd like to note that I bought a car repair manual and went ahead and tested the the crankshaft position (CKP) sensor connector with the voltmeter and got 0 volts with the Key on and engine off, so I assume this is the problem.

Would a bad CKP (crankshaft positon sensor) be the problem for my issues?

New fuel pump, fuel lines and filter all sensors checked ok on scan. Fuel pressure at rail goes no higher then 30 psi. Also does the fuel enter or exit the fuel rail through the pressure regulator?

Hi and thank you for answering I already tried that I should have put that in my question. We even replaced the pcm. When it happens if I release the pressure from the rail the truck will start

Yes it is we actually replaced it with a known good one just in case it was bad. Even left the pressure guage on it held 30 psi for over 6 hours. Im thinkiing maybe the garage accidentally switched the feed and return lines to the rail when they replaced them. Do you know if the fuel flows into or out of the rail at the regulator?

I have a 1994 Ford Explorer that gives a code 341 and will only fire for a brief second on initial startup. Things I have already done: 1)New battery and clean terminals. 2)Relays checked ok. 3) changed fuel filter.
4) Fuel pressure holds at 40 psi during cranking. 5)get spark at coil on all three banks of coil while cranking. 6) tested 12v and signal at injector with logic probe-receiving both 12v and a signal during cranking. Also tach on car works during cranking.
As a final note, car will run with starting fluid which leads me to believe some type of fuel injection problem. Any ideas?

Updated 11-13-09

The fuel pressure stays at a constant 40psi. I also checked and bypassed the fuel reset button but still no luck.
NEXT?

Fuel pump weak. Pressure is too low.
Thanks

My pressure gauge stayed at a constant 40psi. After tapping into the fuel rack with a known good fuel pump, the car is running. The tap block on my pressure guage has a check valve in it that I missed.