280z Fuel pump issues

[280]

So I decided to start a new thread under the fuel injection section because its not related to the electrical section where I resurrected a thread from the dead.

280,

I realize this thread is several years old but this where i got at by >searching< Im having the the same problem. I had a buddy of mine put his finger on the inlet of the fuel pump and he only felt suction while cranking. I tested all the fusible links inside the passengers compartment and all have continuity. With the key on the on position I held open the afm flapper and the fuel pump ran. I dont want to crank the car since its night but tomorrrow morning i will test some more. With the fuel pump relay/injection relay and the ignition ON is the pump suppose to build pressure for a few secs and then shutoff before starting the car? Is this my problem?

Zed Head,

Your results show that the parts you tested work correctly. The fuel pump runs when cranking. When the engine starts, you let the key go, but the AFM flap is open now from air flow and the fuel pump keeps running. If the engine dies, air flow stops, the AFM flap closes and the fuel pump stops running. So no problems with your fuel supply to the fuel rail, at least from the fuel pump outlet.

280,

Not exactly. Once I let go of the key from the "start" position and stops cranking the starter/engine the fuel pump also shuts off. Therefore the car dies after a few secs. The fuel pump is new and i added a new fuel filter. I had also added a clear fuel filter before the fuel pump but removed it and just stuck the inlet hose into a fresh clean fuel tank. I also have a fuel pressure gauge connected after the fuel filter. It reads about 38psi if i leave the pump running without cranking the engine.

Zed Head,

I had a similar problem where the air flow would not hold the AFM flap open far enough to get it off of the cutoff switch, so the engine would not idle at low RPM. It ran fine, just wouldn't idle.

If the fuel pump keeps running when you hold the AFM flap open as you described, you should be able to keep the engine running by holding the throttle slightly open after it starts (which should open the AFM flap), or turning up the idle speed with the idle screw (same effect). If this works, then you might have a vacuum leak, which is letting too much air past the AFM flap. Find that or the adjust the fuel pump cutoff switch mechanism.

My problem started when I advanced my timing. The engine needed less air to maintain idle speed so the AFM fuel cutoff switch started killing the pump at idle. I ended up bending the switch mechanism so that it would stay closed at lower air flow.

You can see the cutoff switch and how it works underneath the black cover on the side of the AFM.

[280]

I went ahead and checked and turned the idle scew up so it can hold the throttle slightly open. The car turned on and died again. I hook up the fuel pressure gauge directly to the outlet of the fuel pump and it reads about 60 psi. I then hooked it back up after the fuel filter (in the engine compartment) and it reads around 40psi. The problem is that it slowly starts losing pressure. Is it suppose to do that with the car off? I think it also starts losing pressure when i start the car thats problably why the car slowly dies. I do notice I have 3 vacuum lines loose but i doubt that has anything to do with it. I will post pics of where the lines are lose if you guys can guide me as to where they go. and the third one comes out of the passenger firewall above the heater hoses. They all lead into the vacuum tank. But as far as losing pressure goes does that mean the fpr is bad? or the fuel injectors are leaking? I remember using a stethoscope and hearing all the injectors clicking intermittently .

[FastWoman]

I'm totally lost in this thread, but I can help you with the vacuum hoses. These control your heating/AC system. 1 supplies vacuum to the system, running to the check valve, magnetic vacuum switches and vacuum reservoir on the opposite side of the engine compartment. Those feed a like that goes through the firewall to supply the mode control vacuum switch (off/vent/ac/heat/def/etc). They also feed a line that comes back to #2, which pulls up the idle when the AC compressor is running.

[280]

Ok so the vacuum lines wouldnt affect the cars operation so long as theyre plugged? Anyways I found out that i had a clogged return line after the regulator therefore it was building backpressure. Now I have a steady 36psi after the filter but now the car doesnt want to start. It starts for half a second to 2secs but then dies.

[Z train]

You do know the fuel pump on these cars are wired to run ONLY if the motor is turning-right?

[280]

Yes that is correct, the contactors are in the afm so i simply hold the afm flap open to run the pump with the ignition ON. So the problem isnt the pump anymore it looks as if its working fine. i thought i was losing pressure because of the pump. However now that i have fixed the prressure issue, I cant seem to get the car started. I crank it and it seems as if it turns over but dies again after a second or two. Im sure im getting spark and fuel. Im thinking its something I may have moved or something all the connectors on the manifold/head seem connected. What else could it be ?

[FastWoman]

You might have air in your fuel rail. If you can find a way to deliver 12V to your fuel pump to run it for 30 sec or so, you'll purge (almost) all of the air and can probably get a clean start. You can jump a wire straight from the (+) battery post to the (+) on the fuel pump to do this.

A remote possibility, but... If the engine still does the same thing, you MIGHT have a problem where the ECU isn't being triggered by the ignition signal. There's a wire connecting the (-) post of the ignition coil to the #1 terminal of the ECU. The signal through this wire increments the ECU, so that it injects fuel every third spark. Anyway, if you don't have signal through this wire, you'll only get a touch of fuel when you first turn the key. It will be from the cold start valve at first and then will only be from the tiny bit of fuel that dribbles past the injectors while the engine sits. The longer it sits, the more fuel will dribble, and the more energetically the engine will first fire up before dying. Anyway this happened to me once (no connection between coil and ECU), and that's how my engine responded.

BTW, I used to have a big problem with air in my fuel rail before I replaced my fuel pump check valve and all my injectors. As a temporary measure, I installed a fuel pump primer switch that would deliver +12 to the fuel pump relay's coil. It made restarts SO MUCH easier, especially 20-30 min after engine shut-down (which was when I had the biggest restart problems).

[cozye]

I vote water temp sensor. Check it according to FSM and make sure your connections to it are good. If the water temp sensor is disconnected or bad, it will dump a ton of fuel into the motor and you will have a real hard time getting it to idle.

If this suggestion, or the other good suggestions made don't yield anything, then just go through the FSM procedure for testing the EFI after verifying good spark.

Also, you need to tell what year 280 you got. Their are subtle differences in the EFI between each year.

[280]

its a 77 i do have power to the the ignition as per fsm test . The coolant temp sensor also reads out fine. The tps is opened and positioned as it should be. I just keep running around in circles with the fsm and troubleshooting.

[FastWoman]

Try unplugging one of your injector connectors and sticking the wires from a Christmas tree light bulb (one of the tiny ones) in it. Crank your engine, and see if the bulb flashes repeatedly. If it does, then your ECU is triggering your injectors. If not, then you've got further diagnosis to do.

[280]

I guess a 280zx afm works better than a 78... i switched them around and the car fired up. But when ever i give it throttle i get a cloud of black smoke.

[cozye]

That's because the AFM has to match your ECU. AFM's even in the same year are not interchangeable always.