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AFM Wired Backward


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Hi there, 


1982 280zx Turbo


Car was running rich at idle, then it seem to switch to running lean at high rpms once it built boost.  I was going through the engine bay and replacing connectors, they had started to degrade, some were missing clips and some had started cracking, I also was cleaning connections starting with improving the electrical connections to see if that cleared up my issues.  I was doing one connection at a time, and then testing the car so I would know what fixed my issue, if anything.  


First item I rewired was the AFM Connector.  Fired the car up and it ran terrible and was smoking.  I shut it off and started to look.  I realized that I had wired the AFM backwards.  So if - was = to an open pin on the connector, and | was where a connector was an occupied pin, I wired it |||-|--, instead of --|-|||.  I rewired it properly and restarted and it continued to run very poorly and die.  


I have checked the ECU where I though a resistor maybe had blown

I had replaced the Fusible Links with a maxi fuse set up and those checked out. 

I ran through the FSM Tests for the AFM and it has checked out fine. 


Im not sure where something else could have went wrong.  I am imaging the engine ran very lean when I had it hooked up backward and that explains the smoke out of the turbo and Intake so I could have done serious engine damage.  


I need some ideas of where to go from here.  Is there something else inline with the AFM that could have been effected by my mistake? I havent tested fuel yet, but that wasnt a problem just minutes before I miswired the AFM.  I have ordered a Fuel Pressure Gauge.


Any help would be appreciated. 




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On 4/9/2023 at 1:32 PM, Kendall said:

So if - was = to an open pin on the connector, and | was where a connector was an occupied pin, I wired it |||-|--, instead of --|-|||. 



On 4/9/2023 at 1:32 PM, Kendall said:

run very poorly and die


Can you show the actual pins on the AFM?  Might be a clue.


Also, more detail on how it runs might help.  Might be something simple like something else you did at the same time but might not be correct.  Like a temperature sensor.


The pin numbers should be molded in to the connector on the AFM.



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Thank you for the replies.  I've photographed the AFM connector and also drew a diagram of what I did.  


When I say its running poorly, its barely staying running and smoking out of the air intake.  Very weak idle, and when I give it a bit of throttle, it barely will rev up then die.  


Thanks for making me photograph the AFM, once I drew this diagram I know what wires I crossed, but I do not know the consequences yet.  I wired connector pin 34 to the wire that was supposed to get connector pin 33, so pin 34 and 33 were swapped, wired backwards.  The other wires on the connector 1 and 2 that were supposed to go to pins 32 and 25 were not connected to anything this AFM only has 4 pins.  


It was idling a bit rich around 1500 rpms before I changed the pigtail on the afm.  It was leaning out at high rpms when boosting.  It ran at this baseline right before I changed the AFM pigtail, this was the first electrics part I changed trying to fix a rich running condition.  I was planning to start the car and test it after cleaning or replacing each part so I would know what, if anything, fixed it. 


Thanks again!  Pics below



image0 (4).jpeg



Edited by Kendall
correcting pin numbers
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Funny that I posted the EFI AFM drawing instead of the ECCS drawing, but the EFI numbers match your picture and the ECCS numbers don't.  I got the drawings from the 1982 FSM Engine Fuel and Emissions chapter.  Page 80 and page 96.  I posted the ECCS wiring below.  Different numbers, but four pins.


Either way though the pins run through a resistor, the AFM carbon trace, so there should be no chance of an over-current condition.  Could be that a diode circuit got reversed in the ECU.  (Edit - or a capacitor.  One of my first electrical circuit experiences was connecting a radio condenser up backwards and having it blow up in my face.   Pretty sure my father was messing with me...) I'm not deep on electronics.  Looks like you got your power supply and return circuits reversed.  No idea what that would cause.  The ECU's were pretty primitive.


It's too late (in the evening) for me to logic out what's what but the air temperature sensor is on the 33/34 circuit.  So 33 and 34  is probably ground.


Anyway, if it was mine I'd run through all of the tests again.  And, if possible borrow a turbo ECU to try.  Seems difficult though.  @cgsheen knows the ECCS system pretty well.  He might have some thoughts.



Edited by NewZed
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