Fuel Injector Signal

Hi all you experts,

Here's my problem: 2000 Frontier XE 4cyl. automatic. Vehicle starts and runs, but number one cylinder is not firing. Through considerable troubleshooting I have determined its not the injector, compression, spark. It's the signal.

I confirmed this with a Noid light. The test revealed that the injector is receiving power all the time and apparently not receiving the ground interrupt signal from the ECM. Again it is only the number one cylinder. So, where do I go from here? Is it the ECM, or some other signal or short that could be the problem?

Thanks for you help!!