FI Connector Electrical

[bjreed1119]

Greetings all.  My wife and I just bought a 1978 280z (MT) and this is my first post on the site.  I’ve been changing out the fuel injector electrical connectors with a Bosch upgrade part.  I can tell that a previous owner had spliced in a pigtail connector, and having seen what he did with other electrical work, I decided to check his work by going to the FSM wiring diagram and testing which of the two wires goes to the terminal on the ECM connector. 

The wiring diagram for each injector identifies two wires, the left wire connects to the dropping resistor, while the right wire goes to the ECM connector (in the wiring diagram I've attached, for fuel injector #1, “Black 37” goes to the dropping resistor and “Black 15” goes to terminal 15 on the ECM connector).  So when I checked the terminals of each connector with my multimeter to the ECM connector, the wiring of the injectors was not consistent (4 injectors had the ECM wire going to the left terminal on the injector, and 2 injectors had the ECM wire going to the right terminal on the injector).

Here are my questions:

1)         Does it matter which terminal the ECM wire connects to?  If the ECM wire is just supplying the ground to a coil, is the direction important?  I think they should be consistent—and plan to change that when I build the new connectors—but will it hurt anything if it is on the “wrong” side?

2)         If the direction is important, what is the “correct” side for the ECM wire to connect to when looking at the actual fuel injector?  For instance, when looking down at the injector, does the left terminal on the injector (the one nearest the front of the car) correspond to the left terminal on the wiring diagram, and does the right terminal on the injector (the one nearest the firewall) correspond to the right terminal on the wiring diagram?  Is my labeled pic of the injector and connector correct?  

Any help would be greatly appreciated. 

[Dave WM]

Should be interesting to hear what others think. Its just a coil, but reversing the polarity will of course reverse the direction of the magnetic poles created when energized. That being said I assume the moving part of the injector is NOT a perm magnet but rather just an iron plunger, therefore reversed poles should not matter. I think the real issue is prob just to avoid confusion anytime someone is trying to diagnose an electrical issue. So if you are using the FSM to check connections it would be nice to have them wired consistent with the diagram.

Edited July 12, 2017 by Dave WM

[siteunseen]

I went by this when I replaced my connectors but it's been years ago so I can't remember right off the top of my head.  Read through this but it looks like the 12 volt faces the front of the motor.

http://atlanticz.ca/zclub/techtips/injectors/connectors/index.html

[Dave WM]

while on the topic the polarity issue at hand is regarding only the FI, other places like switches are a different matter, specifically the thermotime, I think Blue mentions this in the write up. On that one there is a heater and a switch, don't think you would want to mix those two up.

[Captain Obvious]

bjreed1119, Dave is correct in that there are no permanent magnets involved, just a steel plunger that is pulled by the electromagnetic coil. With that in mind, the polarity doesn't matter.

Only thing that I might wonder academically about is that there may be some small amount of residual magnetism retained in the injectors after being used in one direction for some time. Not sure how much of an effect that might have, or how long it might last until the fields have been readjusted.

When I redid my harness, I found most (but not all) of the injectors were wired the same polarity. So when I rebuilt things, I wired them all the same, using the predominant polarity. I think I kept four the same and switched the remaining two to match the other four.