Zed Head

Did you seal the edges of the large vinyl/cardboard panel on the inside of the hatch? The hole for the hatch latch will suck fumes in to the hatch framework and then around the panel edges.

The tachometer circuit resistor is by the realy area/fuse box wiring. It's a lump inside the harness, with a female and male bullet connector. Dig it out and branch your pin 1 wire to ground through that resistor.

I've found in the past that the ECU is sensitive to the quality of the Pin 1 signal. I can't really say how, but I do know that I had two situations where the engine would not start when the tachometer was disconnected even though the path to Pin 1 was still intact. Reconnected the tachometer, which is on a branch of that circuit, and it was back to normal. The fact that you got the injectors to fire by grounding coil negative shows that the ECU "sees" what it should from the coil negative but it's not liking the signal. But I've also had an engine on a stand with no tachometer start and run using a separate EFI harness. In that case I ran a wire through the 2.3 kOhm resistor on the tach circuit to ground. My theory was that the ECU needs that constant high resistance coil ground circuit to operate right. You might try getting the tachometer circuit to normal, if it's not. Or even add a capacitor or a high resistance path to ground on the Pin 1 circuit. I've fixed a bad tachometer by adding a condenser. It's pseudo-voodoo 'cause I don't know why it works but it won't hurt.

Dude. Jai's not a dude. Those plugs are very fouled. I'd install new plugs, take it for a good drive, make sure it gets nice and warmed up, then pull them and see how dirty they are. Looks like it's running very rich though, unless you're burning oil. Does it use much oil? They really should never get that dirty unless there's a problem. A short test run on new plugs will give you a good clue though. tx is right about the leak. At least you know it's hose-based. Those are both low pressure hoses, one is 5/16" and I think that 3/8" works on the other. The 5/16" is a good fit, the other is a bit tight, if I remember right.

Three years man, three years...

Actually, that's a sign that the thermostat is not working correctly. You might not even have one. The thermostat is designed to stop coolant flow until the engine heats it up. Normal temperature is about 180 degrees F.

Couldn't get through it. Could you state the issue you're working on so certain key words will pop out of the pile? Not giving you a hard time. It is seriously unreadable. Or you could edit it in to paragraphs. Think I found it - " I fired up the car and noticed excessive exhaust noise coming from the engine. " and " alas, the noise persists". You need to add more detail about the noise.

Wow, that is almost a perfectly square, unbroken block of letters. It fills up all of my computer screen. Kind of neat to look at, but it also looks like about three meals on one plate. Could take time to consume before you get some feedback. Just an aside...

You can stick a piece of tape or plastic over the male part of the pin also to break contact.

Still unique to 75.

You know the 75 driveshaft flange and diff flange are unique to 1975, right? The bolt pattern and size. You can't swap a 75 driveshaft in to a 76-78 280Z.

Nissan stopped using the mustache bar in 1979, so whatever you got wouldn't be what we know as a "mustache" bar.. And the 1986 halfshafts are CV axles and won't fit your 72, bolt-wise or lengthwise (too long). If you got the stub axles from the hubs I think that those are only usable with an adapter. The 86 CV axles will still be too long. So all that's really "swappable" from and 86 300ZX is the diff, with no axles inside. You really need to find an old 280Z parts car to get what you need. Unless you want to buy aftermarket. Here's a pretty good old writeup. It takes some reads and re-reads to really get a feel for what matters and how to do it. In principle it's very simple,but there are a lot of things that look like they should fit, but don't. http://www.zhome.com/ZCMnL/tech/R200.htm

Actually, what you want is an R200 insulator for a 280Z. If you're installing an 86 300ZX R200 diff in your 72. (Assuming that you have the mustache bar). One option - https://www.nissanpartsdeal.com/parts/nissan-insulator-diff~55415-n4300.html Part #16. I don't know why there are so many revisions for the part. Maybe because the early designs used weak rubber? Who knows. http://www.carpartsmanual.com/datsun/Z-1969-1978/axle/rear-suspension/16

There's some good AAR stuff in here -

There's a "pre-muffler" that looks like a converter. It's there to cancel out droning from the exhaust system. Looks like a converter but it's not. There should be a sticker. A clogged muffler would be like a clogged converter though. So maybe...

There's a sticker on the driver's side door jamb that will tell if you have a converter. It was California only in 1976 so you might not have one. I think Nissan called it a Catalyst back then. Mine says NON-CATALYST. Are you saying that engine won't even start now?

But the one you unplugged was the messed up one, right? I think that Dave might be the other guy that could have unplugged his BCDD. Some day I'll unplug mine and see what peahens (picked the wrong suggestion. You know what I mean).

I think that the proposal is (at least mine was) that disconnecting the wire would change the quantity of air bypassing the throttle blade. Significantly enough that it would change idle RPM. Not while driving but while sitting in neutral. Unplug wire idle changes, plug it back, it changes back. It was just a thought that it might be one cause of the BCDD causing a high or a low idle. The "relaxation" that you feel is the fuel coming back on at 2800 RPM. All the car reviewers hated it.

Now you can take the old one apart and see if a diaphragm is blown or the vale is just clogged or stuck. So, to summarize - you swapped an 80 BCDD,with no solenoid, in place of a 79 BCDD that had one. So now you're using a BCDD with no speedometer control. It's parts car anyway, but curious... Don't forget to inspect the 79 distributor breaker plate and bearings. If you get there soon enough you might be able to save the bearing cage before it breaks.

That's one of those interesting things. They stopped using the solenoid in 1980. Looks like they only referenced one side of the blade also. A new puzzle. In 1981 they put the BCDD on the bottom of the intake manifold. Seems like they never quite got it where they liked it. Some designs last for years,like the AAR. This is the problem with the BCDD - you can get drawn in and spend a lot of time here, for little value. Like eating celery.

So if the pin is retracted, in it's normal position with the key On (the click you hear when you turn the key On) and at a stop, you would expect a small amount of air to bypass the blade. But that extra air is normally present and baked in to idle speed adjustment. If the wire is disconnected the pin blocks the passage and idle speed should drop a small amount since that extra air is gone. Does that follow? I should be able to go out and disconnect the power wire and see a drop in idle speed. If you have an idle, at a stop, that's stuck high, it seems to also follow that it's probably the main air bypass, designated by the arrows in the picture, that is stuck open allowing air through. Or a hole in a diaphragm, or the main valve n the BCDD is stuck. Seems like there are two normal ways for air to get through the BCDD, the little control passage and the main bypass passage, and one abnormal way, a hole. I've never thought the idle hanging problem through completely, I just refer to what other people said.

Major edit, too many words. Wouldn't disconnecting the power and unscrewing the adjustment screw remove it's ability to change function. Making it a permanent throttle blade bypass? Like the idle air bypass, Readjust the idle screw and you're done. Turn 6 way out or way in, and 20 to reset RPM. Maybe. Seems like the increased idle speed must come from the small passage to chamber 17. With no solenoid that passage is always open. I think, I couldn't make sense of the FSM words.

The EFI FPR's work by bleeding off excess pressure. So without a return line there's no control mechanism, no where for the excess pressure to go. Could be that an FPR before the rail with no return line is actually not doing anything at all. Max fuel pressure is probably determined by the pump's internal pressure relief. I'm not sure how other FPR's work, but that's the principle behind the EFI units. That's why if you block the return line the pressure rises to the pump's max. And the fumes have to be going somewhere. They probably just get purged away from the vent exit quickly if you don't smell them. Or you smoke. The purpose of the charcoal canister is to store them until they can be sucked in to the engine. For the environment.

I didn't read the article I just worked from the basics. If you measure on a low pressure day, you'll get a different reading than on a high pressure day. If you want to work with a voltage or resistance, without converting to pressure you can do that. Your assumptions are complicating things, along with unclear thinking. What's the set-point of your "switch", for example. If you haven't done your measurements yet then you shouldn't be making decisions about where you'll get the air. That's how good science works - set up your experiment from sound principles, use good equipment, take your measurements, and draw conclusions. You've already decided that the engine bay is "bad" without knowing anything. That's bad science. but it makes a ton of money for K&N.

The "CAI" thing is a market mainly produced by K&N. To go along with their filters that let more dirt in. Those guys have made their millions selling things that probably do more damage than good. Most cars already have a remote entrance for air. Once the car is moving the air in the engine bay is replaced. With cool outside air. But, you can get MAP sensors from places like DIYAUtotune. You'd want two, one to measure a reference point and one to measure the new location. Just like the O2 sensor, you need software to process the signal. https://www.diyautotune.com/shop/sensors-data-logging/temperature-and-pressure-sensors/