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My cars Fuel pressure is not rising with boost. Any ideas what it could be?
2002 Ws6, 346, D1SC kit, 15psi, running E85, Deka 80lb injectors.
F.P. at idle is 58psi
Key on, Engine off, F.P. is 50psi
When I bought the car, it had a single Racetronix 255 kit. I added another Walbro 255 pump.
The FPR vacuum line goes to a 6 port block, along with my boost gauge and BOV.
I tried moving the FPR vacuum line to the intake manifold and that did nothing.
The relay wire sizes are this: Maybe the sizes are too small???
the positive off of the 255 pump that goes to the relay is a 14ga wire
the negative off the 255 pump that goes to chassis ground is a 12 ga wire
the wire that goes from the relay to my fuse box is a 14 ga wire
the wire that goesfrom the relay to the the positive battery post is a 12 ga wire.
The ground coming off the relay that goes to the chassis is a 12 ga wire
thanks for any help
Last edited by 30th t/a; Oct 23, 2020 at 02:22 PM.
You need to reset the FPR. You might have to upgrade your wire harness to a dual wire harness in order to supply enough power to each pump.
Racetronix recommends connecting the fuel pump harness wires directly to the alternator rather than the battery. Their single and dual harness kits use high strand count 10 gauge wire.
How large is the vacuum hose that is the primary source for the vacuum block? I use the brake booster hose as the vacuum source and T off of it with a 3/8 hose to the vacuum block. I'm using four vacuum ports - Hobbs switch, FPR, Boost Gauge, and ATI Bypass Race valve.
Last edited by dlandsvZ28; Oct 24, 2020 at 02:27 PM.
Reason: edit content
Thanks for the reply.
Yes I will look at resetting the FPR.
Im not sure what size the vacuum line is but it looks indentical to your vacuum line.
I have a 6 port vacuum block similar to yours.
The original Ractronix pump has its own wiring harness that it came with. I installed another 255 pump and it uses its own wiring but Im wondering if the wire size is too small.
Also - The little piece of fuel line that comes off the fuel pump and goes to the "T" fitting...I wonder if it could be kinked where the bend is at.
Thanks for the reply.
Yes I will look at resetting the FPR.
Im not sure what size the vacuum line is but it looks indentical to your vacuum line.
I have a 6 port vacuum block similar to yours.
The original Ractronix pump has its own wiring harness that it came with. I installed another 255 pump and it uses its own wiring but Im wondering if the wire size is too small.
Also - The little piece of fuel line that comes off the fuel pump and goes to the "T" fitting...I wonder if it could be kinked where the bend is at.
If the wire harness that you built for the second pump isn't pretty much configured the same way with relays and wire size as the Racetronix hot wire kit, then IMO the second harness is suspect? Are you sure that it is coming on at the set boost level? How did you test it?
IMO, the Racetronix dual wire harness for dual pumps is a good harness for dual pumps, because in a matter of you seconds you can test each pump simply by switching the harness plug ends. Each harness end has it own fused plug in connector to complete the circuit. In pic red is for the primary pump, the blue harness plug end runs from the second pump to the Hobbs switch. The second pump fires at 4 psi. See pic.
How are you measuring your boost? Are you sure it is 15 psi?
How are you measuring your fuel pressure at 15 psi of boost?
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Fuel pressure not rising with boost?? Any ideas? 
