So I've had this problem a while now. Done some searching but found no case of this exact issue and I can't remember anyone talking about this one.

The Z starts right up and idles smooth. Then I hear the fuel pump noise go away (or almost away) and a couple seconds later the idle starts to stumble and drop. This looks just like I have lost fuel pressure.
I can either let it stumble and most times it will suddenly kick the fuel pump on just before the car dies and then the idle returns to normal.
I also can tap the throttle and the fuel pump turns back on.

I removed and cleaned the ECU, AFM, and TPS plugs. All looked great.
No change there.

The car will do the same thing while driving steady. If the throttle is moving at all or under boost it never has an issue.

On rare occasions the car will start up and drive fine and never do the above mentioned stumble for the remainder of that drive. But if it starts doing that fuel pump thing right away, it will keep doing it every 6 seconds the entire time I'm driving. Sun, rain, or snow don't seem to change anything. Weather its cold or warm, been driving recently or not doesn't have any consistency with the issue coming up or not.

I pulled open the AFM and watched it. If I move the arm inside manually while the fuel pump is off, this does not turn the fuel pump on. I had a theory that my throttle tapping was moving the AFM flap and that somehow told the fuel pump to turn back on. Not so.
The AFM looked super clean too. I slid the sensor bracket up slightly for a clean connection but no change to the problem.

The fuel pump relay I can hear go on and off. What actually controls that relay or tells it when to turn on high/low? I think there is a lower setting for idle and maybe that part of the system is broken or going out?

 

The 280zx turbo uses a fuel pump module (right above the ecu) to control the fuel pump. I burnt one out a few years ago & the pump would not turn on at all. Might want to check it's wiring & also pull it apart (quite the task actually) to check the board.

Or... toss it and upgrade to the Z31T ecu.

 

I was also thinking that my time might be better spent on doing the 300ZX swap. So I take it the Z31 doesn't even use that module.
All I need are those 6 drop resistors and a Z31 wiring diagram... I think.

I have 1988 ECU (with plug), MAS (with plug),Z31 chopper wheel, Power Glove, and 8-bit Nintendo.

 

Whats your oil pressure?That can shut off the fuel pump too I believe.

 

Indeed. The Z31 ecu controls the fuel pump.

 

Oil pressure is up. Normal operating pressure at idle or cruise. I've even changed the oil since this whole issue started in December 2008.

 

No R.O.B? No Power Pad?

 

You know the Power Pad wont' work in the Z.

but no, I don't have a R.O.B. yet

 

What about the turbo controller!? gotta have one of them

 

 

no NES Advantage???



or maybe the car doesn't need an extra "SLOW" button .

 

Maybe the fuel pump relay?

 

Ok... BUT WHAT ABOUT THE ZAPPER!?
lol

 

That fuel pump controller is hard to get out. There is one bolt on the top side I can't reach at all.

poo

The Zapper didn't help with removal at all.

 

Hmm OT but would the fuel pump controller be the problem if my Z doesnt prime properly? its turns of for like a split second when I turn the key on and thats it still I try starting the car.

As for the bolt, maybe you can get at it with a few U-joint sockets, or maybe a ROB and reach it for you lol

 

I bet ROB would work perfect. I can't find of them. They're pretty rare. Although I'm not sure I want a robot for a garage assistant... have you seen the iRobot movie?! scary stuff...

My turbo Z still primes properly every time. The fuel pump relay turns on and off so I think it is working fine. Its whatever sends a signal to the relay. The ignition, ECU, and pump controller all are interconnected and control the relay and the voltage to the pump. I just read a bit in the Factory Service Manual about that fuel pump controller.

When I did my turbo engine swap, the fuel pump relay is part of the ignition and dash wiring harness so it opperated on its own without a fuel pump controller as part of the system. I installed the turbo ECU without that controller and it worked fine. Now I'm working with an original turbo Z.

I bet my controller is switching the fuel pump from 14.4v down to an error of 6v or less instead of 9.8v
It sounds like when I bump the throttle, the controller kicks back into "battery voltage" mode.
The controller is fed by the CHTS and the crank angle sensor. Besides the controller being bad I guess I should check the CAS plug.

 

go to a J yard get a diffrernt EFI relay and Pump relay.
for one its cheap and for 2 you'd know for sure with out ripping into any thing just yet.
couple people at the old club had a similar problem with a car, got some mixed results but some one had the relay go bad.

not to mension they are both tied into the fuel system and are between where you could have a problem and the power source.

 

I see plenty of 280ZX's in the local yard but never a turbo 280ZX. The fuel pump controller in question is unique to the factory turbo models.

However, a light bulb came on and I have an idea on a work-around using some Nintendo products. I'll get to it today after work and report back.

 

Still not fixed.
I inspected the fuel pump relay (and the two blue relays next to it) and even the two relays behind the battery. (one of those I think is the EFI relay) A couple of those had pretty bad corrosion on them. I cleaned them up good but the car still operates the same.

 

bypass that module, take #27 and go to either #6 or #18. or both in combonation. while its running normal you could check each of those for power and tap #27 into that particular one. you dont even have to fully remove the module until after you test that bypass works. i did it with my intermitant wiper control module when it burnt out. dont forget to wear the glove when working and a groud strap.

 

the FSM shows that the controller sends a ground signal to the relay. I had thought it was sending power. Its nice that the 300ZX turbo sends the same to the relay.
Anway, after checking every other possible connection I went back to the FP controller and unplugged it. I found that the large white wire was the signal to the relay. I grounded it out and the fuel pump stays on while the car is on.
I'll leave it like this for a while and drive it. No need to replace the controller. I'll just get my Z31 ecu put in this summer.

 

^^^ Good find!!!!

 

Have you checked for any vacuum leaks? I had this come up once when I was at the drag strip and turned out to be the rubber accordian boot to the turbo had developed a crack and was making my Z not idle. It ran fine under boost like yours or if I blipped the gas, but coming to a stop guaranteed me idle issues. Also, hook up a fuel press gauge if you can so you can monitor the fuel pump's activities.

Also, have you changed the fuel filter and inspected the connections at the fuel pump along with the fuel dampener? Just curious! Hope you can get it fixed!

 

Its fixed and running great. It was an electrical problem turning the fuel pump relay on and off.

 

Cool, glad it's running fine man. So when is the estimated date to the jump to Nintendo power? I'm sure you're getting tired of that Atari 2600 ecu. Pong and Frogger can only keep you entertained for so long. BTW, you can get the dropping resistors at Radio Shack or Frys. They are about a $1.00 a piece. Use the same ones specified by JWT in their pdf sheet for the 450hp ecu setup. Can't remember off hand what the resistance values were.