Frying ground wires and extreme slow cranking...

[EverRude]

I am attempting to swap a L28ET from an 81 280ZX to my 75 280Z.

 

Not going well. I won't attempt to explain everything because it's too much.

 

My first priority is to get the car to crank. As in, starter spin the motor from the ignition switch.

 

However I am burning ground wires at my Ignition system plug. Pics are below and hopefully you'll understand. You can certainly see the ground wire that burned completely into. At first I just got a slow crank and I noticed the smoking hot ground. This ONLY happens while cranking. Not with the key in the ON position.

 

Now the day before the car cranked fine. But I hadn't swapped over the turbo coil/ignitor. I had to completely remove the coil bracket to make the swap. I didn't know how much of the original wiring I needed so I just swapped the coil and ignitor onto the original bracket with the original wiring. Only the ignitor was actually added. I made sure the coil bracket was grounding but I could remove it all again and clean off all paint to be sure there's good contact.

 

I managed to comletely burn through the ground wire when I attempted to troubleshoot the slow cranking by jumping the +post to the solenoid. I had the start sensing wire disconnected. Only the ground at the starter mount bolt and the main +wire from battery were hooked up. However there was the main W/R wire tied to the +post on the battery so that's how the rest of the car got power. It cranked a little faster then slowed again. That's when I smelled the smoke.

 

BTW I disconnected the rest of the harness from the battery and ONLY powered the starter. Motor spins fine when jumping the solenoid.

 

So as you can see I am totally screwing this up. The schematics don't do me any good. I look at the 81 and 75 stuff and wires colors don't always match what either says. Which just leaves me futher confused and frustrated.

 

Anyways here's the pics of my coil as it's currently set up and a pic of the ignition plug with the toasted ground. I'd appreciate any help.

 

[Geking]

Have you looked into the start ballast resistor bypass? When the 280z was in a normal running state, it sent the pulse for the coil though a ballast resistor (under the coil, rectangular.) My guess is, you have the system wired into a short, but the resistor is saving you normally at the run, but at start, the car bypasses the resistor and goes right to the coil. Check your voltages at run, see if the resistor is heating up...

 

Just a hunch, I could be quite wrong.

[bjhines]

Very slow cranking gives it away.

You have a poor block to chassis ground. Look for the big black wire that usually runs from the Battery NEG post to the bolt that holds the starter on the block. Clean it, replace it, or go find it in that box of parts and install it.

[EverRude]

Have you looked into the start ballast resistor bypass? When the 280z was in a normal running state, it sent the pulse for the coil though a ballast resistor (under the coil, rectangular.) My guess is, you have the system wired into a short, but the resistor is saving you normally at the run, but at start, the car bypasses the resistor and goes right to the coil. Check your voltages at run, see if the resistor is heating up...

 

Just a hunch, I could be quite wrong.

 

I'll check this out. Because whatever I did it happened after I swapped coils and messed with the wiring to the bracket. I can't test anything "at a run" because this car isn't close to running at all.

[EverRude]

Very slow cranking gives it away.

You have a poor block to chassis ground. Look for the big black wire that usually runs from the Battery NEG post to the bolt that holds the starter on the block. Clean it, replace it, or go find it in that box of parts and install it.

 

 

I thought so too. The first thing I did when I got the car was swap the battery cables (this was about 2 days before the motor swap and eveything cranked fine after I changed the wires). That wire to the starter is new. But when I encountered this problem the first thing I did was disconnect it and clean everything.

 

I even added a second 1 guage ground from the block to the firewall. There was already one there at the battery side. I added this one closer toward the driver's side.

 

It really seemed that all the cranking amps are trying pass through that 14 guage ground wire under the dash. In fact, if that ground wire isn't hooked up the starter won't spin when the main harness was connected to the battery. The car cranks fine with the battery powering only the starter.

[bjhines]

Try hooking the big ground so that it's lug is actually in contact with the starter housing. In other words get the washer and bolt stack so that the cable lug is the first thing against the starter housing.

[EverRude]

Try hooking the big ground so that it's lug is actually in contact with the starter housing. In other words get the washer and bolt stack so that the cable lug is the first thing against the starter housing.

 

That's how it is. Remember I disconnect the main harness from the battery and the car cranks fine when I jumper the solenoid. If I hook up the main harness (large white wire with red stripe) jumping the solenoid does nothing. It's like all that cranking power is attempting to go somewhere else but only when cranking. Nothing is smoking with the key in the "on" position. If I replace that ground at the ignition harness plug I'm sure it would begin turning over slowly again and burn out that ground again.

 

Something in the starting circuit is shorted. But I have no idea what.

[Daeron]

It sounds like you may be experiencing some issues from vesitgial remains of the starter interlock system.. a woeful, godforsaken bit of bastard engineering that Nissan blessed us with for a few model years in the mid 70s.

 

I can't help you track the issue down, because I am about to careen headlong into the same problem the next time I start playing with MY 75.. but the fact that your starting amp issue goes away with the harness connected makes me wonder if the car is hampering something through design (the flawed design of whatever may remain of your interlock system) rather than through fault (ie, short somewhere, "magic wire," gremlins)

 

Dunno if this will help any, but since I encouraged you so much into this project I feel obligated to try at least

[EverRude]

There's one thing I noticed after the swap that could be related to my problem. There was a wire connected to the negative battery post via a blade connector that's not currently hooked up. I can't find that wire. Is it stock and does anyone know where it connected to? Here's a pic.

 

[Daeron]

My stock battery cables are long gone, but I know there was a fusible link connected to the positive cable for the EFI system, and it looks an awful lot like what you pictured...

 

Have you looked over the troubleshooting sections in the FSM for "slow cranking while starting" for any other leads? I don't know how much it will help, but tomorrow I will pop my hood and see if its worth it to take any pictures of my car. I THINK there was another grounding point on the negative cable, that I just ran to a chassis ground, but I may be mistaken.

 

Any chance of a better foto of that errant wire? The plug REALLY looks alot like that fusible link I mentioned, and your description fits the bill perfectly, other than it being on the negative wire. Any chance someone else swapped the battery leads somewhere along the line?

[EverRude]

Found the problem. It was that wire with the bladed connector at the neg batt post. The reason I couldn't figure it out was because the wire on the old harness was red. I didn't remember a red wire going to the neg batt post. I would think that would kinda be noticeable.

 

Anyways a friend and I ran continuity on the bladed red wire on the old harness. It was ground to every nearly every pin on the ecu connector.

 

So we used that wire and spliced it into the main ground harness in the bundle of wires that runs down tha passenger fender well below the battery.

 

Worked like a charm. Motor cranks normally and no smoking wires. Hoorah.

 

Also figured out my fuel pump wiring. Now I can troubleshoot the rest of the EFI harness using the manual.

 

Progress. Yay!

[Daeron]

woohoo!!! NOW its time for some progress, the gremlin is extricated!