1997 A6 Quattro Wagon

CEL came on P1602. I found the battery to be the wrong one for the car so I cleaned the terminals and put a new correct battery in. Cleared the code, but it returned. Moved on to checking the ECM harness. I found that someone had already tampered with the ECM, and it looked likelit got really wet at some point. I cleaned up the terminals with electronic cleaner. I reconnected everything, cleared the code, but it came back. Pulled the ECM opened it and cleaned inside reconnected everything, cleared the code, but it came back. Replaced the ECM. It was fine for a few days, but the code came back. So I went back to the battery and removed the smaller wire attached to the top of the + terminal to clean any corrosion that maybe in there since I knew the post parts were clean. Reconnected it, and now she just cranks with no start. I don't hear the fuel pump it smell fuel. I tried both ECMS, locking and unlocking the door 3 times (immobilizer light not on) d disconnecting both battery terminals for 30 minutes, and turning the key on for 3 minutes. Any suggestions?