Strange NEW electrical problem??

[TomoHawk]

That's why the search feature is your good friend here, and why you'll get a lot of people ask you to try it before posting your question, because 99.9% of all issues you will get on the S30 have been discussed and/or solved.

BTW- the current version of the Adobe PDF reader has the ability to print posters, so you can enlarge your colored circuit diagram to 2x4 pages (landscape), using 48% scale and .6 - 1 inch overlap. Print it all out, then glue them together, and you have a fancy color Z poster!

P.S. You'll do yourself a big favour by getting a cheap notebook and sketching the individual circuits before you work on something. Note the wire colors and such.

Edited March 15, 2013 by TomoHawk

[Zed Head]

The ring at the AFM is actually one end of a two-ringed wire. One ring on the AFM body, one on a mounting screw.

The Engine Fuel chapter has a decent diagram of the grounds for the EFI harness, from the ECU. Doesn't show you where the connection is, but you can verify them all at the ECU connector..

[mgood]

Here are is my and mjr45 in the same image. Remember that mine is a 11/75 - 76 280. The small harness goes up to connectors under the top radiator hose. Second picture. If I remember right there were 4 wires in the little harness. The hoses do seem a little different in their location and number.

Also thanks everyone for the favorable comments about the engine bay, it takes a lot of work with it being Zebarted when new.

[Captain Obvious]

The ring at the AFM is actually one end of a two-ringed wire. One ring on the AFM body, one on a mounting screw.

Haha! Excellent! So in light of the additional info, I believe that those ring terminal grounds do NOT come from the EFI harness and I stand by my original claims:

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.

How do I know? Why do I care? Because my PO messed with the electrical system on my car, and I've spent some time trying to piece it back to the way it should be. And this thread is helping me a bunch because I've long known that he messed with the wiring up around the coil and AFM. Not quite sure yet exactly all of what he did, but I know it's not right.

My car currently does NOT have a ground strap on the AFM, but I've got this misplaced ring lug groung coming off on one of the timing cover mounting bolts? I also have a completely unused foot long piece of wire with empty ring terminals on both ends (obviously is supposed to be a ground somewhere). I don't know where this stuff is supposed to go, but this thread is helping.

So, keep discussing!! Please!

And mgood... I third the comments about the beautiful engine compartment!!

[Wade Nelson]

If I had to guess what was wrong with your Z, BEFORE having read all this thread, I'd immediately suspect a grounding problem.

I would make sure your ground from your battery to your chassis is good. And unbolt, clean your main engine ground as well.

Your problem SEEMS to come when your body, touching the fender, grounds the EFI harness. That suggests the EFI harness is not correctly grounded, via

either the chassis ground, or the ring terminals discussed in this thread.

I cannot count how many times I've removed chassis grounds and found them bolted to paint. You take an angle grinder (wheel of death!) and remove the paint,

add a star washer, THEN bolt them back down. Body shops are the absolute worst about this since the lowest paid flunky is the guy re-attaching all the taillamps, ground connections, etc.

In my "X" years of auto electrical experience, "weird" behavior has almost INVARIABLY been caused by poor or non-existent grounding. So that's the place you start.

My other #1 lesson is don't INSPECT grounds, disassemble and clean them. You really can't see what's underneath in most cases.

[Captain Obvious]

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.

I would not add any grounding wire to the EFI system without very careful consideration. Pardon the geek based thread jack...

the ECU is a precision analog system which does some of it's signal processing at very low levels and Bosch (who I assume was pulling the strings at Hitachi) paid careful attention to where the ground currents are flowing. When you're acting on analog signals, current through any resistance (including resistances to "ground") cause voltages to occur where they might not be wanted and this can cause errors in the system.

For example... They were very careful to segregate the injector current from all of the other currents flowing through the system.

They were also careful to create their own ground connection for the AFM and air temp sensor.

On paper, all of the grounds are connected together. And with an ohmmeter, that truth can be verified. But... just because they show as connected, and measure as connected, doesn't always tell the whole story.

You don't want the headlight current flowing through the same ground that the temperature sensor uses...

[Captain Obvious]

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.

Let's hope that you did in fact find the root problem. Do you have any pics of the stuff you found when you unwrapped the FI harness?

[TomoHawk]

I wouldn't suggest that you grind off paint to make a better ground connection under a screw. Removing the paint helps the body to rust. Instead, clean the threads of corrosion as well a you can, and use a non-corroded screw.

[TomoHawk]

There is a heavy black wire in the injector/sensor bundle to the intake with a ring terminal- where does that connect to?

[Captain Obvious]

There is a heavy black wire in the injector/sensor bundle to the intake with a ring terminal- where does that connect to?

Not sure... My 77 has no such wire. Have you got a pic?

[Wade Nelson]

I wouldn't suggest that you grind off paint to make a better ground connection under a screw. Removing the paint helps the body to rust. Instead, clean the threads of corrosion as well a you can, and use a non-corroded screw.

Grind the paint off, use a star washer, bolt it down tight, THEN hit the whole assembly with a little spray paint to prevent future corrosion. The contact points (ring terminal against washer, washer against body) need to be bare (shiny) metal to bare metal; simply relying on the threads of the screw to conduct adequate current (with minimal resistance) is inadequate IN MY EXPERIENCE, which is substantial.

[Wade Nelson]

I would not add any grounding wire to the EFI system without very careful consideration. .

I'm going to CONCUR with Captain Obvious.

Grounding needs to occur in a STAR or a TREE pattern, with the "trunk" of the tree connected to the battery minus post.

If you went in and added ADDITIONAL grounds in the fashion you suggested, you would most likely create a "GROUND LOOP", that is a circular pathway whereby electrons could chose from multiple paths to get back to "ground."

You want to avoid ground loops at all costs. Thats why all grounds are done in "star" or "tree" patterns, so there is one AND ONLY ONE path back to "ground."

Ground loops make nice AM radios, both broadcast and receivers. They'll make your existing, in-dash radio whine. They'll cause EXQUISITE feedback in guitar amplifiers. They make the ECM misread sensors. There's very litte in terms of circuit malfunctions that a ground loop cannot cause.

In THEORY, wires have no resistance. In reality a 1000' spool of 14 AWG wire has about 6 ohms. That's small, but significant.

When you flow 100mA of current through 6 ohms you get .6V of voltage DROP. That's more than enough to make headlights dim, or make the ECM misread sensors, and consequently, inject the wrong amount of fuel.

Give electrons TWO ways to get back to "ground" and you get a differential current, some flowing down one path, some flowing down another. And that's where all the fun begins.

So what you want to do is clean up and FIX the original, factory grounding scheme on your vehilce rather than adding additional grounds. Sure, take out a 14 awg wire and replace it with a 12 or a 10 for a better, less resistance ground path. Clean up body grounds, add star washers. Take ring terminals and buff them with sandpaper or steel wool before snugging them down.

There's a lot more to this than I can explain in a short blog post, but I've given you the basics. One (and only one) path to ground, clean connections, fat wires.

Edited March 16, 2013 by Wade Nelson