 If it should, at least it should idle. Something's going on there. If there's no back pressure, it's not going to read correct with the O2 sensors, and that's going to cause it's not going to see how lean or rich it is. It's got to have that, or it's got to be custom programmed. You can run it with open headers if you have it custom tuned. When you bought the harness, did they do something with the computer or not? Well, I had to go to a different computer. They recommended the GM one. Actually, I got it from you guys.