Z dies after warmed up 77 Z Drives For About 10 To 15 Minutes,then Dies.

[240260280z]

The early 77 used the switch in the AFM to shut the fuel pump off. The logic was that if the car crashed, the engine would stop and not draw air. These caused the AFM door to shut and open the contacts in the switch that send +12V to the fuel pump.

Later 77's used a pressure switch on the oil pressure sensor (next to oil filter). The logic was that if the car crashed, the engine would stop and not pump oil. This caused the pressure to drop and open the contacts in the switch that send +12V to the fuel pump.

[240260280z]

Most 280z problems seem to be dirty electrical connections!

[rcb280z]

Yeah the 8/77 through 78 280z fuel cut off is through the oil pressure circuit. You'll know what you have by looking at the harness connector at the AFM. If it is a 5 pin you have the later 77 through 78, IF everything is original.

 

Mine is a 5/77 and I have a 7 pin connector. The extra 2 pins are the fuel safety cutoff in the AFM. 

Edited March 10, 2015 by rcb280z

[Captain Obvious]

I posted this in another thread where there seems to be fuel pump issues, but it's applicable here as well.

 

The AAR (you know what/where the AAR is?) is wired in parallel with the fuel pump. You can pop the connector off the AAR and probe the connections inside to see the same signal that the fuel pump should be seeing. Put a little noid light across those two terminals if you get energetic. Something you can see easy from the driver's seat.

 

So just like the fuel pump, the AAR should have 12 volts across it's two terminal connections:

 

- any time the key is in the START position, and/or

- any time the key is in the ON position and there is air flowing through the AFM.

 

So, if you've got power to the AAR at the correct times, you're looking for a bad fuel pump or connection to it. But if you're not getting the correct signals at the AAR either, then you've most likely got a problem with your FI relay.

 

Would be interesting to see what happens when your car shuts off from lack of fuel. If the AAR still has power but the fuel pump has stopped is a different issue than both the AAR and fuel pump losing power at the same time.

[Crazy477280Z]

Both AAR and fuel pump lose power when EFI relay loses power. Ime thinking that it has something to do with power supply to EFIrelay.After car started,and then died, I replaced EFI relay with brand new one instantly,and was still at no start condition. I can let it sit for 5 or ten minutes,then turn key to start position with starter solenoid unwired,and still am able to hear fuel pump running. I can then start it up,and it runs very well but then just dies. I still have spark at coil though, so Ime thinking[and I might be wrong about this as electrical problems are my weak point] that the ignition portion of COMBO relay is still getting power while fuel injection side loses it due to bad,corroded,or weak connection. Is there a fusible link between battery and ignition switch,or between ignition switch and EFI combo relay? I dont want to have to hire an electrician for this as Ive never had  to do that before. Ive worked on  every car Ive owned for the last 34 years with help and advice from wherever I could get it.This one is very uncommon,and is beginning to mess with my head. No one seems to have had this particular problem before,so its a mixture of reasonable deductions and alot of testing wires for good connections and continuity I guess.I will post again if I can find something new or definitive as to problem.             

[Zed Head]

The EFI relay has its own fusible link(s), inline from a wire connected directly to the battery positive post.  The link has its own blade type connectors.  Green wire.  There might be two, side by side, some time between 1976 and 1978 they added one.  That might be your problem, they are in a dirty, corrosive spot by the battery fumes.

 

Follow the wires connected to the battery positive post and you'll find it.  You might be on to something.

[Crazy477280Z]

If it is there its buried in the middle of wiring harness,because all my wires on pos. side are wrapped to within 6 inches of batt. Doesnt seem like a good idea to cover a fusible link like that, but it looks stock to me. I will unwrap it tomorrow and see what I see. Is there any chance it might be under dash on passenger side where harness comes through firewall? I dont know if manufactors would put a fuse link on inside of car,but I sort of doubt it.

[siteunseen]

Here's something that may help, especially #13, http://www.classiczcars.com/topic/40658-fuel-pump-and-relay-problem/

 

I've seen those connectors at the battery crumbling apart.

[Crazy477280Z]

Yeah, that has alot of info that might prove useful. Thanks siteunseen!!

[Captain Obvious]

The fuel pump control side of the FI relay does have a fusible link between it and the battery. It's the driver's side rear link of the four on the wheel well. If you've got 12V on both sides of that link while the problem is occurring, that's not the problem.

 

So are you familiar with the numbers on the FI combo relay? Here's the pin numbers related to the fuel pump and AAR:

- Pin 73 is power from the battery. Should be hot at all times.

- Pin 76 is the control signal from the ignition switch. Should go hot only in the START position.

- Pin 36 is the control signal from the AFM. Should be hot only when the AFM is passing air.

- Pin 74 is power output to the fuel pump. Should be hot in START and when the AFM is passing air.

 

The system works like this...

 

Power comes from the battery through the driver's side rear fusible link to pin 73. When either control signal (pin 76 or pin 36) goes hot, the relay connects pin 73 to pin 74 which then goes to the fuel pump. So when either in START or when the AFM is passing air, pins 73 and 74 are connected together and that sends power to the fuel pump.

 

So in your case, one or more of those four pins isn't working properly. Either because of a wiring or connection problem or a problem inside the relay itself.

[Zed Head]

#4 and upper right should help.

[Captain Obvious]

Zed Head, About the info you posted above... Yes, you are right that there are actually FIVE fusible links on the EFI cars with the fifth one coming directly off the positive terminal of the battery. That's the one you identified as #4 in the sketch.

 

But...

 

That fifth link (item number four) runs the injectors and a bunch of other stuff related to the FI system, but it doesn't power the fuel pump directly. It DOES supply power to the AFM switch, so it does provide the primary side control power for the AFM signal once the car has stopped cranking, but other than that it has nothing to do with the fuel pump. The fusible link that directly runs the fuel pump and the AAR is the driver's side rear link located in the fusible link blocks.

 

Also note that the link that runs the fuel pump and the AAR is the one in the schematic you posted. Also interesting to note that the other FI link (item number four) that comes right off the battery is not shown at all on that schematic.

 

Haha! Don't mine me... I'm just trying to make things more complicated by making them simpler! 

 

On edit - I fixed an overextended statement I made prior.

Edited March 11, 2015 by Captain Obvious