So with the old lift pump and modified overflow valve with Bic pen spring, it idled in the 40-42 psi range and ramped up to about 50 psi free revving in park.
After adding the 5x.018 injectors, I was losing fuel pressure fast and the truck was cutting out and popping 2800+. Basically there was no top end fueling.
What I did is tapped into the factory steel fuel line right below the driver's seat with 3/8" fuel line, from there it flows through a 1/2" brass check valve and then 3/8" line to a nylon tee. From the tee, 3/8 line straight to the stock lift pump. From the stock lift pump, stock steel line with banjo bolts to stock fuel filter, from fuel filter, stock steel line with banjo bolts to the injection pump. In short, I simply 100% deleted the stock fuel bowl and added a brass check valve and a tee with 3/8" line.
Back at the fuel tank I drilled a 5/8" hole in the top of the tank and installed a home-made 1/2" copper draw straw. From the straw, 3/8" line runs to a Holley Blue lift pump mounted on the frame. After the Holley Blue, 3/8" line runs to the nylon tee that ultimately feeds the stock mechanical lift pump.
With this setup, the truck can start, run, and daily drive with just the mechanical lift pump system. When I need extra lift pump pressure, I can flip on the toggle switch for the Holley Blue.
With the new mechanical Cummins lift pump alone, this system idles at 50 psi. It ramps up to 55 psi if I free rev it to about 2500 rpm and it holds pressure during a free rev to 4300 RPM. Under load WOT, I can pull fuel pressure down to 15 psi and although the truck no longer sputters and cuts out, it still feels soft on the top end above 2900 rpm or so.
With the Holley Blue feeding the system, it pressures up the tee flows down to the checkvalve and stops from backfeeding to the tank and feeds up the tee to the injection pump. With the truck off the fuel pressure gauge taken at the fuel filter outlet banjo bolt reads 10 psi.
With the Junker running and Holley Blue turned on, I show 60 psi at idle and 70 psi at 2500 rpm free rev.
Running down the highway WOT with Holley Blue turned on, fuel pressure pulls down to about 45 psi. Obviously the pusher pump tremendously increases the efficiency of the factory mechanical lift pump.
And man have I created a monster! The next track day isn't till Nov 18th, but I think the Junker is finally ready to go fast.
My best guess is that the Holley Blue Pusher pump created 100 HP at the wheels. Not that the pusher pump is a big HP adder, just that the factory lift pump cannot keep up with this hungry 160 pump and keeping adequate lift pump pressure is helping the rest of the setup fuel like it should.
I've never truly been scared driving around in my Junker until tonight.
