AFM/ Fuel Pump

[Packerz]

Thanks Zed and Grannyknot!  Please excuse my confusion re: purpose of my postings....   my bad!
This all is a safety issue and includes my inability to positive identify which TB and AFB I actually have... are there visual differences (obvious external and/or internal components Z/ZXT) I can identify so I can ask for assistance knowing what I truly have.  Was PO using a 75-78 280ZAFM and just attaching it to ZXT TP?. Trying to understand why AFM posts are currently bridged anyway...A difference in using existing 75-78 wiring bundle connections to different TB?  Could current Z wiring bundle itself be modified or totally different bundle in ZXT?

If easy fix (using correct model TB/AFM) doesn’t solve issue, I will need to ask your details of have to go the route of relay tapping into alternator, alternator light or starter ...when engine stops so will fuel flow at AFB, or ideally FP itself?
Or locating a correct SX TB and all component connections and wiring to 75-78 wiring bundle...or will I have same wiring issues.

Sorry about my confusion!!!-  Really trying to be more defined in my confusion and find best resolution   Doug P.

[Packerz]

44 minutes ago, EuroDat said:

Could use a 78 280Z oil sender switch to activate a relay and the relay then bridges the two wires in the AFM.

Just saw this...some questions remain but helps a lot!   Thank you!

[Zed Head]

The factory AFM's have stickers with part numbers on them.  The ZX and Z TB's look different.  A picture or two might help identify them.

If I had the car and wanted to do what you're tying to do, I would "unbridge" the AFM pins then start the engine.  If it starts then dies, repeatedly, then you'll know that the pump gets power at Start.  You can also disconnect the starter solenoid and turn the key to Start to see if the pump gets power.  that's actually simpler, but you have to pull the correct wire.

If you have Start power, then either of the two relay suggestions should work, but you'll have to learn some basic wring skills.  It should be simple to do though, and cheap

If you don't have Start power then you'll need to wire in another relay.  Again, simple, but takes a little work..

[EuroDat]

15 hours ago, Packerz said:

Just saw this...some questions remain but helps a lot!   Thank you!

The fuel injection relay is a complicated unit and has safety features which you should not bypass. Simply bridging the 36 & 39 terminals in the AFM is not a good idea.

An easy way to fix it would be to use these wires to activate the pump thruogh the original efi relay.

Basically if air flows thruogh the AFM these contacts close and allow the pump to run. Terminal 36 needs 12 volts to do this.

I would use an oil pressure switch from a 78 280Z, 280ZX or 84 maxima. It has a sender unit plus a contact to ground.

You could find one in a junk yard or buy a new one. Use that to activate a bosch relay coil 85 & 86 and run the AFM 36 & 39 terminals through the bosch relay 30 & 87 terminals.

 

 

Edited June 14, 2020 by EuroDat

[Packerz]

WoW.  Thank you! EuroDat !!!  I can follow this and I think I have a 78 oil pressure switch somewhere in my Zar parts stash. I never used it because of twin leads... maybe I was closer than I thought??.  Will get a friend to show me electrical connections using this “roadmap”.  Thank you, thank you.  Kinda still curious why PO bridged pins to begin with.     Doug P.

[Packerz]

EuroDat, please forgive my lack of auto wiring knowledge!  ?  Does the 78-ZX Oil Pressure Sending Unit have two yellow/black stripe (positive?) leads and one (thicker) black ground wire exiting the sender? The thicker Black wire ring grounded to engine block?  I’m having difficulty getting from 1st diagram to 2nd with only single Y/Black stripe wire.  My 77 wiring harness only has one Y/Black stripe output wire into wiring harness (then bridged to Pin 36 & 39 AFM?). Is Y/Black stripe currently sending power (Into Fuel Pump Relay wiring then exiting out onto the AFM (bridged-both positives?) pins into internal meter relay? Why bridge...to get two positive pins out of one wire?  Where would (what later model color wires) would go into AFM harness to pins 36&39 
what is Figure 3 ? I don’t see either 36 or 39 wires into/from 85-87&30 wires and relationship of This diode diagram to OPSU Through to AFM...
Your diagram is great!...this just my own confusion on one/two wire conversion!  ??Doug P.

[Zed Head]

You will have to run your own wires from the oil pressure switch to the relay and from the relay to the AFM plug wires.  Your 77 harness only has oil pressure sender wires.  The switch came out in the 1978 model year.

Also, if I remember right, the oil pressure switch is normally closed (as the drawing shows).  It opens when pressure is built.  Your friend who knows wiring will need to know this to make the relay work correctly.

[EuroDat]

If you still have the original oil pressure sendrr for yhe 77 it will have one wire. You can connect it to the 78 sender by swapping the wire terminal to the spade type.

I made a simple diagram to explain it better.

 

[Packerz]

Beautiful (and really understandable even for me!)?.  Does “ new” diagram eliminate relay wire #87a shown in first set of diagrams?.  #86 flows constant 12v (coil ballast next to AFM=good location!) to AFM pin #  36.... couldn’t figure out what #87a was “spliced on 87’s post for.   Again thank you!!!   Doug

[Packerz]

Would anyone have the recommended Bosch/Bosch style relay model number for this procedure.  Or will just any 4 or 5post relay work?  Is there a specific amperes requirement to open and close relay? 30/40 amp OK?  shouldn’t  I try to locate an all-weather relay and harness since I Think I understand this will be an under-hood location near coil/AFM?  I think this is my last Question. Thanks all for patience and help!!!    Doug  P. 

[EuroDat]

It doesn't have to be a Bosch relay. Any 5 pin relay will work. Easiest is to buy one with the harness plug. The relay in your screenshot will work, no problems. They call them bosch style relays, not necessarily a Bosch manufacured relay.

https://heielectric.com/shop/electrical-products/relays/5-pin-relay-kit-12v-30amp

In this example the 30 (yellow) would go to your trrminal 39. The 87 (red) would then go to terminal 36. The 85 (brown) would go to the ignition coil power and the 86 (blue) would go to the terminal on the oil sender.

I would mount the relay close to the AFM , somewhere between the AFM and ignition coil. That way the wiring will be as shorg as possible and only one long wire to go over the engine to the oil switch.

A 30A relay is overkill, but that is standard issue. You are only bridging the 36/39 terminals to activate a coil in the EFI relay very similar to the coil on the 85/86 terminals.

 

 

Edited June 15, 2020 by EuroDat

[EuroDat]

Btw. The terminal 87a is not used. Just fold that wire back over itself and tape into the harness.