I asked this same question on the c4 forced induction forum too, but I know a lot of people here have this gauge.

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.

 

I have the same gauge....both senders are the same and can be used for either boost/vac or f pressure.

You need to read the instructions as far as calibrating the gauges

You need to calibrate or zero the gauges with the gauge on, but car not running. Fuel pressue gauge should be done with the sender disconnected from fuel rail, otherwise there will be pressure in the rail (C5)

Your boost gauge can't be plumbed into the brake booster, it needs to be attached to a port that will see boost,like in the manifold, post blower

hope that helps

 

I have the same gauge as well, but I did not know these two important details...THANKS RICHARD, it does help

 

Not trying to nitpick, just clarify I have seen many people use "tap into the brake booster" and "tap into the brake booster line" interchangeably. You really can't tap into the brake booster itself unless you drill and tap the metal unit.... which would be a bad idea

The brake booster line or brake booster hose leading up to the brake booster is a great place for boost signals going to wastegates, gauges, etc. In fact several kit manufacturers make or sell a log that fits the 5/8" (or was it 1/2"?) brake booster hose and has several 1/8 NPT ports for just this purpose.

The check valve on the brake booster hose is right at the end of the hose, and inserts into the brake booster itself. Therefore everything leading up to the brake booster itself will see boost and vacuum.

 

Thanks Tony, now I feel 50% better Great talkin to you Thursday, Thanks for Your Time

 

My bad

I was thinking pd blowers, where brake booster line connects just post tb and not what I would call the ideal place to measure boost. I suppose that with an oem style manifold, anywhere in the manny would do.

 

did you ground the gages?

 

I grounded the black wire connected to the main connection. I did not run any additional wires to either of the sending units.