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Dave WM

280z AFM lead?

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while I have been looking over what seems to be some non OE wiring around the dizzy term block I came across this pic in the FSM. I see the lead coming from under the AFM a single wire that looks like a locking spade connector. I think the PO replace this with a ground wire (has eyelets one side bolts to the bottom of the AFM the other side to the chassis ground thru a mounting bolt that secures the AFM mount to the chassis). Can someone confirm this is what this wire does? I could not find anything from the wire harness that looks like the pic at the top of the page.

AFM lead.pdf

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That might be one of those FSM errors.  I think that all AFMs use the round eyelet as a ground.  I've seen a lot of AFMs and never seen a wire with a connector coming through the hole in the AFM base like that picture shows.

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ok that looks like mine, only diff is the extra ground wire from the green wire on the term block that mine has.

A guess here, the AFM is electrically isolated from the chassis due to the use of the rubber gromments used to mount the plate to the chassis (I presume to damp vibrations). So with all that air flowing thru the alum body of the AFM it could build up a static electrical charge with out the ground lead.

So that lead makes since but my grounding of the diff green wire does not. My play is to get one of the HEI modules as ZH has mentioned just as a backup, will wire it up and just control the coil by choosing which module is hooked up. I read some comments by ZH in another thread where he just left the OE stuff in place and would just disconnect the signal at the OE module and then hook this one up under the hood.

All this is really just so I don't get stranded on one of my long road trips, so a tested backup system would be nice to have.

oh btw my test stand engine does NOT have the AFM grounded, something I will take care of since I don't want to smoke an ECU.

Edited by Dave WM
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I think that spade connector is a legarcy from the early Bosch system they used in the first 280Z's

I have seen it on an Alfa over here.

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Dave, 

I have a very early 75(1/75) and it looks like the FSM, at least the connector ground. No additional wire (green) coming from the terminal 

block. My green wires go into the harness! 

Ron

AFM-gnd.jpg

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well I went out today and tried it again, this time with extra ground (the non OE looking one that goes into the term block green lead) disconnected, and it started right up. Not sure why that was not the case before, but presume it was something else before causing the no start. Anyway I am going to keep that disconnected for now and get some drive time in!

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Dave, 

A couple more photos of what My 75  looks like. No Ground wire attached to the terminal block. Mine is bone stock

Ron

dist-wire.jpg

dist-2.jpg

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I don't recall that large spade connector coming off the harness of mine (looks purple in the pic). I did remove the non OE ground, so far it works fine. The non OE ground may have been causing some issues, as I went to remove it, the poor crimp on the eyelet just let go. Could have been an issue if vibration setup causing spurious signals.

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I just checked my harness no sign of that purple lead with the large white locking spade connector. The harness looks complete with no signs of hacking. If you look at my 1st pic you can see it is missing. Wonder what that is for?

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13 hours ago, zclocks said:

Dave, 

A couple more photos of what My 75  looks like. No Ground wire attached to the terminal block. Mine is bone stock

Ron

dist-wire.jpg

dist-2.jpg

Ok now I am bugged, can you pls take a look at where that large white spade connector goes to? Not usre if that is a purple or black, black I assume.

Another mystery, I do NOT have that ground connection shown attached to the nut under the term block. I have a place for it (the hole on the term block mount) but it is unused.

I checked the FSM engine harness #2 detail B did not show those, but the FSM I am looking at was for 75/76

Edited by Dave WM

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Dave, 

The black wire, spade connector , goes to ground. The attachment of the ground is under the AFM plate, but could go anywhere for ground. 

Again mine is a 75 CA model so it might be different. Couldn't open the BE.pdf. Also is the pdf , the one on line from the OEM FSM? I have a hard copy manual and don't see it if you can give me a page # I can look for it. 

Ron

 

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OK,  I found the page in the FSM , BE 88. It says the spade connector goes to the AF sensor. If you look at the schematic for the 75 280 it shows that the spade connector is ground and goes to the AFM. 

Question : is you take the terminal block cover off is the black wire connected to the green wire?

AFM-gnd.jpg

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On 12/28/2019 at 2:32 PM, Dave WM said:

here is a pic of my setup

 

100_1830.JPG

I'd like to see where that black wire is connected also.  Looks like somebody in the past either made a bad guess or used some bad logic.  Wouldn't be surprised if it was just connected to the cover screw.  Ground to ground.

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Dave , 

Taking a second look at the new lug attached to ground looks like this was a new addition. Can you provide a photo with the cover off the 

terminal block? Also, the green and red wires come from your distributor. If either is grounded then it would be shorting out the spark timing.

 

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it was right on top of the green lead under the block. already removed and discarded (when I was taking it off the poorly crimped on eyelet under the term cover fell off, def not OE).

As far as grounding the green, it worked, I presume the signal wires are electrically isolated, so if only one lead was grounded it still works. I did note that with the ign on engine off, intermittent contact with the ground from the green signal wire would fire the spark. mentioned that a while back ZH speculated that it was just a slight change in the electrical potential from the grounding of the one lead. OR it was making no contact do to the poor crimp, but I doubt that. I have been driving it for years that way, and I am pretty sure when I started down this path of trying to figure out the issue, I did a resistance check of the green term to ground and it was a very low resistance reading that you would expect with a wire to ground connection.

 

Pretty sure I verified the isolation by checking for resistance from the dizzy pick up coil to ground (completely open) same with the term block wires, no ground path on either red or green. That is with the non OE wire removed.

I have no idea what the logic was from the PO on this hookup I am with ZH either a bad guess for just bad logic. Only think I can think may have been an attempt to ground the mount plate with the intent to connect to a body bolt near the term connector. Not needed of course since the correct OE ground wire was in place and attached in such a way as to ground it thru the chassis using the mount screw.

Of course the idea of using the green term block as a ground makes no since at all but, that is the only thing I can come up with. its so obvious that no extra wire belongs there, even just looking at the rubber plug on the side of the tern block you can see cut outs for wires, and you can tell its not cut to allow 3 wires out of the block.

Prob should have a thread for "Mystery Mods by PO's"

:)

 

 

Edited by Dave WM

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I had just removed my AFM a few days ago (to facilitate other maintenance) and there weren't any rubber grommets installed on the mounting bracket screws.  According to the diagram in the Car Parts Manual, there should be 6 total grommets (3 for the screws that screw in a downward direction, and another 3 that are for the screws that screw in from the bottom of the bracket upward).  My car is a 78, and from the diagram it looks like all Zs had this configuration from 02/76 through the end of the 78s.

The rubber grommet part numbers are:

22683-N4201 (3)

22684-N4201 (3)

And, of course, these parts are NLA for purchase (according to courtesy nissan).

Would one of you be willing to post a photo of one or both of these grommets (removed from the bracket) showing enough detail that would allow me find a suitable substitute grommet(s)?

BTW, there was a ground wire attached to 2 of the screws on the bracket, but with the grommets absent, I don't see how it served any useful purpose.

 

 

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Dave, I haven't looked at the design of the ignition modules to see if they reference either side to chassis ground. My assumption is that neither side would be tied to hard to ground in the module. That assumption is based on the twisted-pair nature if the pickup wiring. They are trying to reduce the loop area with the twisted pair and it would completely defeat that purpose if they would tie one side to ground in multiple locations.

My assumption without any reverse engineering is that the pickup inputs are not galvanically isolated (with a transformer or something), but they may feed some sort of floating input differential amp at the input stage of the module. If that's the case, tying one side to ground might not cause it to malfunction, but it certainly isn't necessary or desired.

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On ‎1‎/‎2‎/‎2020 at 10:21 AM, Captain Obvious said:

Dave, I haven't looked at the design of the ignition modules to see if they reference either side to chassis ground. My assumption is that neither side would be tied to hard to ground in the module. That assumption is based on the twisted-pair nature if the pickup wiring. They are trying to reduce the loop area with the twisted pair and it would completely defeat that purpose if they would tie one side to ground in multiple locations.

My assumption without any reverse engineering is that the pickup inputs are not galvanically isolated (with a transformer or something), but they may feed some sort of floating input differential amp at the input stage of the module. If that's the case, tying one side to ground might not cause it to malfunction, but it certainly isn't necessary or desired.

roger that. been working just fine since I disconnected that suspect added by PO ground.

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