Strange NEW electrical problem??

[mjr45]

75 280Z with EFI, new EFI connectors all around, injectors, CSV, thermotine, temp sensor, AFM, TPS, AAM also new thermotine switch, temp sensor, CSV and AAM. Today while tinkering I found out that if I touch the EFI harness wires to the thermotine, temp sensor, the temp sender or CSV, the engine dies. There is no ground wire that I can find on the EFI harness. The engine runs fine as long as you don't touch any of the wires I mentioned. Since I'm basically not very good with electrical stuff I'm lost.:tapemouth

[zKars]

Sure sounds like grounding issues. There most certainly WERE ground wires on the stock EFI harness. Obvious open bare ring terminals with black wires attached into the harness. The ones that comes to mind are right on top of the intake manifold, more or less in the center. Another is on from the AFM harness to one of the AFM mounting bolts, or rather from a simple black wire with ring terminal ends jumper that connects the body of the AFM with its mounting bracket on the body. Its mounted in rubber feet, so it needs that. SHould see a dangler somewhere on that EFI harness. Hunt!

[mjr45]

I've stripped the EFI harness completely and haven't found any ground wire, however the ring clamp that holds the harness to the top of manifold I believe acts as the ground but I have no idea how, if that clamp is removed won't start, if its in place it'll start. I also replaced the bullet connectors to the temp sensor and thermotine, the insulation was cracked and broken close to the connectors. There were also a red and green wire in the harness to the temp sender that had been cut off and just bare ends which I also wrapped with electrical tape to give some insulation. After all the above, I touched, shook, squeezed, flipped about all the wires and no problem. I hope that its fixed, we'll see.

Edited March 14, 2013 by mjr45

[Pomorza]

Mjr45

For what I remember there is a ground from the EFI harness that goes directly to the battery. If you look at my batter in the photo below you can see there is a large black wire coming off the battery. That is the harness ground (EFI computer ground to be exact). I also included a colored wiring diagram for a 76, not sure if the 75 is the same but it can be used for reference. I know you said you weren't good at wiring so I gave you the best thing to start with, a diagram. Everything harness related on the diagram is in white and pretty much in the lower center. Take a look

Hope that helps

Jan

76circuit_COLOR.pdf

Edited March 15, 2013 by Pomorza

[mjr45]

Jan, thanks for the info, and yes on my 75 there is the large black ground wire to the batt neg post which is probably the EFI ground. Wish I had that diagram a couple of weeks ago when I was redoing my interior electrical stuff, it would have made things easier to read.

[Captain Obvious]

I don't believe there are any "chassis" earth connections in the FI harness. I think the only connection to ground is that big wire which connects directly to the battery. From that connection, it splits within the harness to branch out to "provide a ground connection" to a bunch of locations within the system, but that sole connection to the battery is the ground for the whole system. There are no ring lugs coming out of the EFI harness, and the metal ECU case is not electrically connected to the circuit. Basically, if you have a problem with that main ground connection to the battery, there is no other backup which can share the load. And unless I'm missing something (which is completely possible!), the car will not run.

That said, it's absolutely clear that you've got some kind of intermittent connection issue, but I don't think it's a grounding problem.

The thermotime switch should be completely out of the picture unless the engine is cranking, so I wouldn't worry about that.

Same goes for the CSV. Once the engine is running, the CSV is doing absolutely nothing.

The AAR changes too slowly to react as you described. Even if you would disconnect it completely, you wouldn't see any effect for fifteen seconds or so.

That leaves the temp sensor... If you have a shaky connection to the water temp sensor it will cause exactly what you're describing.

Basically, if you open circuit the temp sensor, the ECU interprets that as an extremely cold engine and dumps in lots of extra fuel to account for the low temperature. If, by wiggling the wires, you are breaking the WTS connection, the engine will stall because you're flooding it.

Edited March 15, 2013 by Captain Obvious
I write good

[mgood]

Here are some pictures from my 11/75 - 76 280. Might help.

[Wade Nelson]

Sorry Cappy, but I think you're wrong. There's at least one ring terminal ground in the FI harness, at least on my ZX. Kinda hard to see in Mgood's pictures, it goes underneath the hold-down strap that holds the EFI harness stable (circled) Do you see it now?

And my, my, my. What I wouldn't give to have an engine bay as clean and shiny as that! Wowzer!

Wade

Edited March 15, 2013 by Wade Nelson

[TomoHawk]

AFAIK, there are those two ring terminals; one on the AFM (case-to-chassis), an the one on the harness clamp (main FI ground), on the intake. The others are bullet connectors to sensors and other small items.

If you were to add a grounding circuit to the engine, what size wire would you suggest? I think I would use 10-12 ga stranded wire, and make a daisy-chain from the ground screw (on the firewall by the battery) around to the front (alternator) then over to the dizzy and AFM, then to the intake and cylinder head. Maybe you could then go inside to the ECU case.

Yeah, mgood definitely put in a LOT of time detailing the engine area, People ought to be running over to look a it to learn about their own Zs I had the engine out, and we cleaned, painted, and re-wrapped it all, and it still doesn't look that nice.

Edited March 15, 2013 by TomoHawk

[mjr45]

I believe the temp sensor was the culprit, the bullet connectors had several spots where the insulation was broken and bare wire was visible, the wire at the connectors was also very slightly exposed and nasty looking, so I put in new ones on the temp sensor and the thermotine and hopefully that will fix the issue, we'll see. The AFM has the ground ring in place and there is the wire to - battery in place which I'll double check later today. I am amazed at the knowledge of the members here and always get answers to my sometimes silly questions. Thanks to all of you. You can sorta see the battery connections in this pic. This was before I unwrapped the FI harness.

Jan do you know how I can get a large copy of the your wiring diagram, my computer will only print it on 8.5X11?

Edited March 15, 2013 by mjr45

[Captain Obvious]

Sorry Cappy, but I think you're wrong. There's at least one ring terminal ground in the FI harness, at least on my ZX. Kinda hard to see in Mgood's pictures, it goes underneath the hold-down strap that holds the EFI harness stable (circled)

Haha! Me wrong? Completely plausible. Probable even! mgood's photos clearly show ring terminal grounds. :embarrass:

I believe I have generalized and incorrectly assumed similarities between years. Please forgive me... Here's some input for my defense:

1) That ring terminal connection to ground near the AAR is not shown on the 76 wiring diagram.

2) That ring terminal connection to the AFM is not shown on the wiring diagram either.

3) I've got a 77 and I have verified that neither of those ring terminals exist on the 77 wiring harness.

4) My statement about ground connections holds true for 77. Unfortunately we weren't talking about 77!

Do I get special dispensation since even though I spoke incorrectly due to my over generalization between years, I did nail the root cause of the problem!

[Captain Obvious]

Actually... looking at the photos again, I want to enter an appeal...

In mgoods photos, there are what appears to be TWO wiring harnesses going under that cable clamp near the AAR. There is a large diameter harness (which is clearly the EFI harness), and there's a small (1/2 inch) harness laying on top of it.

That ground ring terminal connection actually comes out of the SMALL harness, not the EFI harness. So where does that other harness go? Does it actually tie into the large EFI harness somewhere out of frame, or is it in fact part of the engine bay harness and NOT the EFI harness.

And what about the one at the AFM? Does that ring terminal actually emanate from the EFI harness, or does it come out of the bay harness?

Huh? Huh? I'll take my lumps, but I want to double check first!