| 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. 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. 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 even a fuel cycles after the new one was installed.
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.
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 increase in pressure.
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. 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.
After the 1 second pressure bump or when the car is turned off, fuel pressure drops quickly at the front gauge but not the rear except when the car is hot. Then it drops a bit but not to 0. 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 when 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. The rear gauge responds exactly as it should, a throttle blip sees an increase in voltage and a jump in fuel pressure in line with engine vacuum. 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 ] Any ideas are welcome because I’m out of them.
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