Just about done with the wiring and wanted to try and fire the engine to make sure all was hooked up correctly. Right now I just have open headers. I was going to trailer it to a place to have ss exhaust installed from the headers back after the initial start. But, I was re-reading the GM engine control harness instructions and it said the exhaust system must be properly sealed or the oxygen sensors may not work right. I currently have a 'start-up' tune on the ECM and was planning on a dyno tune when all was ready. I don't want to take a chance of dumping too much fuel or not enough because the sensors are not reading right. Is this a concern? Should I have the exhaust system finished before firing it up? thanks.