| Sorry to post this in General but the last post in tech didn’t get any replies so I’m trying to reach a wider audience. What happens: Fuel pressure is normal for 10-20 minutes after start up. After that the fuel pressure begins to fall until it’s down around 25 psi at idle. I have an electronic fuel pressure gauge mounted after the fuel filter. I have a manual gauge mounted just off the output side of the pump. Except for the gauges and Nismo injectors the fuel system is stock. What I’ve checked: The fuel pressure gauges I’m using have been verified as accurate.
Fuel pressure regulator swapped out to no effect.
Fuel pressure damper swapped to no effect.
Fuel filter replaced to no effect.
Fuel pump controller swapped out to no effect.
Fuel pump replaced to no effect.
Filter sock on the pump is still dead clean.
Old filter sock was discolored but otherwise clean.
Fuel tank is free of corrosion and there is no debris of any kind in the tank.
Fuel pressure tested on both sides of fuel filter to no effect.
There are no leaks nor a fuel smell of any kind from any part of the car.
Stock fuel lines from pump to fuel filter bypassed with hose to no effect.
Tried it with the gas cap off to ensure there was no overly high pressure build up in the tank and there was no change.
The voltage to the pump is exactly what it should be. A 1 second bump when ignition is turned and 6 volts when it’s idling. It’s a steady 6 volts while idling even while the pressure drops.
All of the connections between the harness and the pump are good. All connections between the pump itself and the plate/mounting bracket that the pump sits in are fine.
Squeezing the return line does cause an equal increase in pressure on both ends (pinch it off to 60 psi at the rear gauge and the front will be around 47 psi).
I have a pair of widebands on the car and they read exactly what you would expect given the fuel pressure issue, fine at first then progressively leaner.
The fuel injectors only have around 30,000 miles on them and ohm perfect, within .1 ohms of each other. I pulled the plugs, pressurized the fuel line and not a whiff of fuel was present in any of the cylinders so none of them are leaking.
The ECU isn't tossing any codes.
After the fuel pressure has dropped off up front the gauge will still respond when you hit the throttle. It responds exactly as you would think it should, it's just about 13 psi lower than it should be. Problems: That 1 second bump that the pump gives when the key is turned to "Run" doesn’t get the fuel pressure any where near 43 psi when it's cold.
After the 1 second pressure bump or when the car is turned off, fuel pressure drops quickly at the front gauge except when the car is hot. Then it drops a bit but not to 0. It will hold 38 psi when it's hot but not running.
It definately has something to do with how hot the car is. As stated the pressure is fine when it's started from cold and then drops as it warms. When started from hot the problem comes back immediately. Here’s the real mind****: The fuel pressure gauge in the rear that is hooked directly to the output side of the pump reads 38 psi steady at idle even after the front gauge drops to 25 psi. I’ve had a hose, a straight piece of hose, rigged between that gauge and the front gauge and I’m still getting the pressure drop. I have no explanation for this. Previous posts: [ http://twinturbo.net/nissan/300zx/forums/technical/view/1055057/Fuel-pressure-code-43-stalling-weirdness.html ]
[ http://twinturbo.net/nissan/300zx/forums/technical/view/1056734/Strange-fuel-pressure-issue.html ]
[ http://twinturbo.net/nissan/300zx/forums/technical/view/1058552/Falling-fuel-pressure.html ]
[ http://twinturbo.net/nissan/300zx/forums/technical/view/1062273/Still-suffering-low-fuel-pressure.html ]
[ http://twinturbo.net/nissan/300zx/forums/technical/view/1062463/Continuing-low-fuel-pressure-and-nothing-left-to-test-WTF.html ]
[ http://twinturbo.net/nissan/300zx/forums/technical/view/1063722/Fuel-pressure-still-falling--out-of-ideas.html ] Any ideas are welcome because I’m out of them. 
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Fuel pressure issue: Day 153 - 
