Like Abacus suggested, check voltage of + at fuel pump at WOT. Hook up a small red wire to the relay pin #87 and run it to radio area where you can connect to volt meter. Then, run brown wire to the rear seat bracket where you bolted for ground. One last wire (use black) to run to radio but this one, connect to battery ground. We suspect you will see less than 13.5V between pump positive (red) and seat bolt (brown). Then try pump positive (red) with battery ground (black) and you'll probably see 13.5V to 14V.
Let us know the results and hopefully, we will see the problem.

 

I will try that in a little bit. What numbers am I looking for and if I’m getting a higher voltage from battery negative do I just run a negative from the battery?

 

You got it!

 

Hey what’s up man,
Ok so I did the test running a wire from the replay #87 pin and used the seat bracket ground and I got 13.2 at idle and 13.3 at WOT. Moving the negative from the seat braket to the battery negative it goes to I get 13.3 to 13.4. When I hook up the voltmeter straight to The battery I get 14.2. I’m confused as to what’s causing the voltage drop

 

Are you saying that you got 14.2V when testing at the battery (+&-)? And you get 13.3V using ground at back seat and battery -? If yes, check the voltage by at after your fuse (+) and back seat (-) to see if voltage is same. If it's 14.2 behind fuse at WOT, then add more wire for +. STM kit uses 10 gauge wire for relay to battery + right? If it's 13.3V after fuse, check your fuse and wire connecting to battery.

 

Yes so when I test the battery when the car is idling I get 14.2 but when I check the positive at the pump I’m at 13.3. I have a 0 gauge wire going to the back I might just see what that will give me volt wise at the pump. I talked to stm and they told me 13.3 volts is more then enough not sure how much of that is true. But it’s frustrating.

 

What is the wire gauge from relay pin#87 to pump white wire?
Add a picture of your setup too.
And what boost and fuel pressure are you hitting?