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Hey guys I have a racetronix 340 pump with Hotwire, regulator, and return line. With stock rails and feed . Car is losing fuel pressure as soon as it hits boost. It ran great for 100 miles . Now going 65-30 as soon as it hits positive vacuum. I changed the fuel filter, and regulator. I pulled the pump and the in tank fuel line is good. Anything else I should check before replacing pump? Pump only has 100 miles on it.
Is this a 99-02 F-body? What is different about the return line from stock? Do you have a fuel pressure gauge inside the car showing the drop? What kind? Are the Oetiker clamps on the submersible fuel hose in the bucket nice and tight? What kind of submersible fuel hose are you using the one that came with the racetronix kit? Verify that it has no leaks. When you first try to start the car does it start right up or do you have to do a key dance a few times to get it to build enough fuel pressure? What kind of fuel pressure regulator are you using? If aftermarket, did you remove the factory fuel pressure regulator from inside the pump bucket? How is the regulator plumbed?
Is this a 99-02 F-body? What is different about the return line from stock? Do you have a fuel pressure gauge inside the car showing the drop? What kind? Are the Oetiker clamps on the submersible fuel hose in the bucket nice and tight? What kind of submersible fuel hose are you using the one that came with the racetronix kit? Verify that it has no leaks. When you first try to start the car does it start right up or do you have to do a key dance a few times to get it to build enough fuel pressure? What kind of fuel pressure regulator are you using? If aftermarket, did you remove the factory fuel pressure regulator from inside the pump bucket? How is the regulator plumbed?
99. The in tank regulator is removed . I had a pressure gauge plumber directly into the regulator showing the drop not sure on the brand but it’s a higher end gauge, borrowed from a mechanic buddy. The factory evap is being used as the return line. Before I tested the pressure I sent my tuner the logs and he said it was dropping pressure . Like I said the car ran great for the dyno and 100 miles after. The clamps were tight, and were actually really hard to get the lines off. It was the plastic line that came with the racetronix kit and I pressure tested it with air, no leaks . It always started right up seemed like it had pressure, I let it prime for a second before turning the key though. The regulator is plumbed on the end of the rail, screwed onto where the valve used to be.
Last edited by Brendyn G; Apr 20, 2020 at 10:58 PM.
Are you datalogging fuel pressure? Otherwise its impossible for your tuner to know from a log, and for you to look at the gauge while driving.
Are you logging battery voltage? What does it do when in boost?
Do you have a reference line going to your regulator? What happens to pressure when you unplug it?
So the aftermarket fuel pressure regulator is mounted just before the feed into the stock fuel rails then and you have the stock evap line connected to the return port on the regulator and the other feed port on the regulator is plugged? Is the stock evap line that is now being used as the return line a straight shot from the regulator to the return port on the fuel bucket top? What did you do with the stock return line that terminates at the "T" located near the factor fuel filter? (#40 in the image below) Did you just remove the "T" fitting and return line while also completely bypassing the stock evap system?
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Fuel pressure falling off. 
