Fuel Pressure and Running Lean Problems - 78 280Z

[z_again]

Hi, been fixing problems on my car since purchase last March. Here is what I have done.

Replaced:

plugs (NGK)

wires (Nissan)

thermostat (Nissan)

rotor

distributor cap

PCV (old one was froze)

air filter

fuel filter

distributor (old one was froze up and vacuum advance leaked, have set timing and am getting good advance now)

vacuum lines

water temp sensor and connector

AFM boot from AFM to throttle body

The previous owner had set the TPS to where it was in WOT mode at all times. I believe this was to mask a running lean problem. Once I set it back correctly I have started the following problem.

My car now hesitates on acceleration and will fire through the intake which would imply I am running lean.

I swapped my AFM with another, no change.

I did all the EFI checks per the bible at the wiring harness connector to the ECU and everything looked ok.

I put a Summit Racing fuel pressure gauge after the fuel filter.

The gauge goes to a little above 36 psi when running the fuel pump without starting the car as per the FSM.

With the car started it reads around 31 psi and will go up to close to 38 when revving the motor. However, last night after warming up, the pressure was around 28 psi.

My question is: what should the fuel pressure be at idle with the vacuum hooked up? I have found varying values from searching, anywhere from 24 to 28 and 34 to 36

Could it be dirty/clogged injectors?

I have checked extensively for vacuum leaks. The car will almost die when removing the oil cap.

I have another ECU but have not tried to swap it yet.

I still plan on taking the fuel pump off and cleaning the screen.

I have not yet adjusted the valves.

Any help would be greatly appreciated.

Les

[sblake01]

The fuel pressure shoud be roughly 37 (36.3 according to the FSM) at idle. And it should pretty much stay there during all stages of operation. The 'rising rate' thing didn't start until 79 w/the ZX and 810. From what you say your fuel pressure regulator is fine. Changing the ECU won't correct a fuel pressure problem. A bad fuel damper, clogged injectors, clogged fuel lines, any kind of blockage in the fuel sytem can cause problems with the fuel pressure.

From the 1978 FSM:

The pressure regulator controls the fuel pressure in such a manner that the pressure difference between the fuel pressure and the intake manifold vacuum is always 2.55 kg/cm2 (36.3 psi).