OBD2 code U0129 - no communication?

In the beginning the car cranked wouldn't start. I checked the fuel, it wasn't getting fuel. So with out checking for spark I replaced the fuel pump, the car started ran about 3 minutes and died. This happened 3 times then it would crank but not start. Checked spark no spark also checked fuel pump again it didn't seem to be responding also. Checked all the fuses and relays that I knew to check all were good. Thought the ECU was bad bought one off of E-BAY used. Not realizing once again that for that year they made many different ECUs. I had thrown away the original, yeah l.O.L. I now know which computer was in it originally I had bought 2 used ECUs. The last one I purchased I took out of the same year vehicle myself it was automatic like mine only difference was power locks and windows, mine are manual not sure if that matters? Also key in and the security system stops flashing and the check engine light comes on which leads me to believe it's not the engine immobilization system?Cranks but still won't start. Read something about adding the car vin# to the new computer, not sure how that's done and will it possibly keep me from having to buy #3? Thanks Again, God Bless anyone that reads and responds to this mess, thank you many times!

I also noticed while cranking the check engine light will illuminate but only while cranking.

Thank you for the information. The fuel pump is under the back seat and I can't hear it running. I can if I wire it directly but the car still isn't starting, I will certainly check the EFI relay. Thanks so, so much. I will let you know how it turns out. One more thing my first question due to trying to be thorough was probably difficult. About programming the vin in the new computer? Oh and the immobilizer system does seem to recognize the key because the light stops flashing when I insert key.

No pin. Only while cranking It will illuminate. Car still cranks but no start.

Sorry just saw this message. I am going to double check that and see before I answer. That is what I was thinking. When the key is inserted and the security light stops flashing the ECU is recognizing the key. Your saying that is correct right? Sorry for the delay I only have time to work on the car Monday through Wednesday and after 5 on Mondays can I start. I am going to check the EFI relay this evening, I will post how things go. Also have access to the OBD2 scanner with laptop hoping for communication. If not I am going to try disconnecting the sensors one at a time hoping if one is bad when disconnected the OBD2 will read and I will know it at least that sensor causing that problem? Thanks again you are a God send!

Engine cranks over but will not start. No communication

Getting fuel, have spark. Good compression. Check engine light does not come on at all. Key on, or while cranking over nothing!

Put code reader on shows error not able to communicate.