I just installed the dual spa gauge with boost and fuel pressure on my C4 with a vortech system. My first issue was that the two sensors appeared exactly the same. After finding a post here that addressed that, I came to the conclusion that they must have been the same. Another post said that it came with one barbed sensor and one threaded sensor. Both of mine were threaded. I wen ahead and spliced one into the brake booster hose for the boost and installed the fuel pressure where in a 1/8 npt spot.

After the I got everything hooked up, the fuel pressure read negative. I figure that I might just need to zero this out. Should I do that with the car off? The boost gauge was more of a problem. At first, it read zero. I reved up the car in the driveway and it still said zero. I went for a drive and it went to 1.5 driving through the neighborhood and stayed there. I know there wasn't 1.5 boost driving 1500 rpms. I got on the road and ran to 5000 rpms and it didn't change. What could I have done wrong with this install. They sensors are connected to the right cable for the applications. I understand that I may have to zero the fuel pressure, but the boost didn't change at all. One weird thing was that the gauge was dented at the back where a post was bent when I got it. The box was not damaged at all which seemed odd. I went ahead and installed it.