Fuel Pressure Issue

Basic tech questions such as future setups, different turbo kits, car diagnosis, etc
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idaxx
NooB
Posts: 2
Joined: Tue Dec 08, 2020 12:54 pm

Fuel Pressure Issue

Post by idaxx »

Hey Everyone, I've been trying to get my ka24det build finished for the past month and have been stuck on an issue I can't seem to find the source. I've got a 95' 240sx. I am hoping It's just me overlooking something very stupid and someone's fresh perspective can tell me I'm an idiot haha

As the title reads, each time I prime the vehicle to start, my fuel pressure jumps to around 40-50 psi then drops to 0 within maybe 3-4 seconds of priming. There are no leaks from the outside of the vehicle at all and all the lines are clamped down properly.


A little background of the fuel-related mods done to the car are:
- Radium Fuel Rail w/ adapter to OEM fuel pressure regulator, pressure gauge
- 1000cc Injector Dynamics injectors (overkill I know but future proof for when I need)
- New OEM Fuel Pressure Regulator
- New 300zx OEM Fuel Filter
- Used Full Blown 340 fuel pump (yes it is used but it came off my brothers Z which had absolutely no problems when used, he had it for about a few months and literally came off his straight into my build within the same day)
- Fuel Pump relay to the battery
- All new hoses on the sending unit assembly and worm clamps
- Used strainer (it is fairly clean no discoloration at all)


I also checked the top of the sending unit and I can feel the fuel being moved nothing is being sent back to the return line which is very odd.

Any help would be much appreciated!
NukeKS14
240sx Wannabe
Posts: 157
Joined: Thu Jan 09, 2020 8:33 pm
Location: Northeastern KS

Re: Fuel Pressure Issue

Post by NukeKS14 »

You only care about fuel pressure with the engine running. My money is on backflow through the fuel pump when it shuts off after the prime.
idaxx
NooB
Posts: 2
Joined: Tue Dec 08, 2020 12:54 pm

Re: Fuel Pressure Issue

Post by idaxx »

Thanks, @NukeKS14, I went ahead and started up it up and fuel pressure held! I assumed that it needed to hold while it primed too.
Just a small oil leak from a line to the cooler but other than that she started like a dream!

Appreciate the help!!
NukeKS14
240sx Wannabe
Posts: 157
Joined: Thu Jan 09, 2020 8:33 pm
Location: Northeastern KS

Re: Fuel Pressure Issue

Post by NukeKS14 »

No problem. I've heard of some people installing check valves in line between the fuel pump and filter. The only reason I'd consider doing that is if you're running dual pumps in-tank connected to the same feed line. It's perfectly fine for pressure to bleed off without the fuel pump on. Glad you got it running. Better to be safe than sorry.
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