Captain Obvious

I looked over the pic as best I could and didn't find anything worth mentioning. Looks great! So you're thinking tomorrow might be the first start try?? What did you decide to do with the EFI temperature sensor? You running the one out the side of the head?

When you ran that test, where did you break into the line out at the wheel? Did the section of lines you were able to blow through include the small "S" bent hardline on the back of the caliper? Or did you split it where the flexible line meets the "S" bend metal line? Kinda running out of ideas here...

Cool. Hope it's as simple as a collapsed hose. And if it is... I'd replace all four of them, not just the one corner.

Yeah, I'd really take a real good look at that flexible hose. I don't remember if I've ever seen it specifically on a Z, but I've seen several cars where those flexible lines had closed down inside and restricted flow.

And by the way... what's the big picture history here? Is this something that just cropped up on a roadworthy car, or have you reached the "brake portion" of a long resurrection project?

Right. If you're getting reasonable flow on one side an low flow on the other, then you shouldn't be looking for an air leak. You should be looking for a restriction somewhere between the caliper and the source. I would look carefully at the flexible line from the chassis to the caliper. And I think your small leak at your pressure switch is something you need to address, but I don't think it's the cause of the big problem you're chasing.

Dropping back a bunch just to be sure... Did you bench bleed the replacement master cylinder(s) when you put it on? Also, you said you went to the old helper method of bleeding with no improvement. When you were underneath bleeding it old school, did you get a good stream of fluid out of the calipers when you cracked open the bleed nipple? Did that stream appear to be the same on both sides in the front?

I get a similar "poof" sound when I hit the brakes and they go to the floor. Although it's from me, and not the car... Sorry, I know it's "too soon", but just couldn't help myself.

I don't know anything about the draw-down hatch mechanisms, but I know a guy who's been working on putting in a linear actuators on his (shaved locks) 260Z. I think he's on his second, no third. Fourth maybe? revision of the project. It's not as easy as you might think. @GGRIII The doors were pretty easy. The hatch has been a PITA.

Understood. I was just thinking maybe you had some measured flow numbers from the two you could compare. I was thinking that could be a data point for someone looking to verify if their injectors are the right ones or not. No biggie. Again, glad you were able to help the OP get back on track!

No, it's fine. They sealed off the other end (the end you can't get a good look at) with a brazed on cap. Not sure why they felt like it needed to be that complex, but that's what they did.

Great question! Thanks Steve!

Except water. Haha!!

Yeah, that's not good. Heat comes from resistance combined with current. If you've confirmed that the current is normal, then you're left with resistance. Have you opened up that switch and had a peek inside? There are plenty of threads on the subject:

12.45V is just fine. As for keeping it cool, I suggest ice cubes. However, if you don't like the wet spots on your pants from the ice melting, you could rig up a small can of R134 and open the valve a little every now and then. Seriously though... That desoldered wire is obviously the result of a fault somewhere generating way too much heat. The issue is if you haven't figured out what the original fault was, there's the risk that it happens again. My first guess would be failing burned up switch contacts inside that switch you pictured. I don't want you to put it back together now and then just have it happen again in a couple weeks.

I've read on the internet that David was messing around with custom roller rockers for the L-series engines. I also read on the internet there were some reliability issues. Do you know anything about the stories? PS - And apologies to the OP for the distraction.

Well THAT doesn't look right! Haha! Couple thoughts. First, before you bother to reconnect that green/blue wire, have you verified that wire actually has the correct battery voltage on it? Should have 12V on it when measured to chassis ground. And second... If that wire got so hot that it desoldered itself before, do you know why? And if so, have you changed something to prevent it from getting that hot again?

Actually POR-15 claims to be flexible. Here's a snippet from their website: POR-15® Rust Preventive Coating is an effective anti-corrosive and rust preventive coating that offers superior chemical resistance due to its dense, cross-linked molecular composition and non-porous attributes. It has the opposite chemistry of ordinary paints. Now add to that POR-15® Rust Preventive Coating incredible hardness, toughness, and flexibility and you have a coating that is practically indestructible. Clearly they can CLAIM pretty much whatever they wish, but "flexible" did make it into their marketing pitch.

Gotcha. Out of curiosity, did you run the same test (using the ECU) to drive the replacement injectors before you stuck them in? Or was it just faster and easier to toss the replacements in and give it a whirl? Glad you were able to get his car running better!

Agreed. Maybe not quite as good as the OEM, but it's probably "good enough" either way.

What Steve said. The GL over at the steering column should be hot at all times. If it's not, you need to move upstream towards the fuse block. And you don't need to check fuses by swapping them into other locations... You've got a meter, right? I bring that up because I can picture a scenario that goes like this: You pulled the (burned out) park/tail fuse and stuck it into the cigarette lighter position. Then you checked the brake lights and they still worked. All completely true statements, but tells you nothing about the integrity of the fuse that came out of the park/tail location. Not saying that's what happened, but simply saying it's possible. Here's a rough non-pretty layout of what fuses do what for the 77 and 78 years. Might help a little?

I think the reason they did the spinny nut on the ZX version is for better thermal conductivity between the head casting and the sensor tip. I think sensor tip is designed to bottom out in the dry hole against the aluminum of the head. And they did that spinny nut thing so you weren't scraping the sensor tip as you tightened the nut. You could hold the sensor from rotating while you tightened the nut. Of course, that would also make it such that the spinny nut would not necessarily bottom out against any sort of sealing washer. I wonder of they used an O-ring seal there instead of a brass crush washer. I've got some ZX stuff around here someplace and if I can find it, I'll take a look. In any event... If you filled the hole with thermal conductive goop it would probably be fine. I can't believe the head temp changes that fast and I can't believe there would be a huge thermal gradient between the head and the sensor regardless if it bottomed out or not. But I wasn't there when they designed it.

Awesome! Glad you got to the root of the issue! You said "They wondered if it was the injectors so they did full spray tests into graduated cylinders for fuel flow, consistency, and volume, and it looked totally fine." Did they run that injector flow test on the car, or on the bench? I'm wondering if they used the 's ECU to drive the injectors, or a stand-alone injector tester rig designed to check things like that.

I just nabbed a pic off rockauto that shows the original ZX version with the spinning body: That said... The part above was the only one that looked like that. Most (all?) of the other aftermarket stuff looked like it did NOT have the spinning nut and could be used in either a wet or dry hole.

I don't know about the aftermarket stuff, but the original OEM ZX sensors are a little different in the way they mount... On the Z version, the brass body portion is all one piece and the electrical guts are crimped to the body to finish the assembly. In contrast, on the ZX version, the tightening nut spins independent of the sensor body. The "body" portion is two distinct and separate pieces. Why does that matter? Because if you use a ZX version with the spinning nut in a wet location like the Z thermostat housing, it will probably leak through the seam between the body and the nut. You could probably use a Z version in the side hole in a P79 or P90 head, but I would be wary of the converse of using a ZX version in a Z thermostat housing. That pic above of the aftermarket ZX sensor looks like it's made pretty much the same as the Z version, so who knows? Oh, and the connector key is in different locations between the two of them. Not an insurmountable issue, but something to be aware of.