91 GP LE engine swap now it won't start

Ok guys here ya go.I have a 91 GP LE with 3.1 engine.Old engine ran good but knocked reeeaaaallly bad. I bought it for $100 and swapped engines with my 91 Lumina. I got the engine in and all electrical hooked up and just wanted to make sure engine would start before I put it all back together. VVVVRRRROOOOOMMMMM engine started beautifuly. Ran it maybe 30 seconds. Later that week I finished installing radiator,air cleaner and such...Hit the key and crank crank crank.but no start.......Changed ingnition module,pcm, to no avail.Now here's my question.I checked voltage at the injectors and only read 1.5 volts...How many volts should be there. Its getting fuel to the rail and getting fire to the plugs. [B]HELP I'M STUMPED!!!!!! Thanks guys

take the plastic cover off the passenger side that covers the ECM (under the hood by the belt drive side of the engine under the radiator overflow bottle. Use a screwdriver handle and tap on the ECM. IF the car starts. contuinue tapping and see if it dies again. If it does, you need a computer. IF the GM service number on your ECM is 1227727, there's a good chance your's is bad, as that particular number is known to fail.

I've replaced the ecm already...that was my first suspect, but no help...I'm not sure how much voltage the injectors need to work...thanks taz