Zed Head

If there's no coolant in the engine it might be that the coolant sensor is getting "steamed", and showing 212 F , from condensing steam, instead of the true temperature. So when you try to restart it's too lean. But that doesn't explain the WOT starting procedure. Not sure what's happening there. You can run straight water with no problems. Are you missing a radiator or something? Another possibility is that the ECU is going bad. I mentioned this earlier but that's one way that they die. They flood the engine to begin as they start to die, then eventually they just don't do anything. I had a 78 ECU do that. It died while I was out testing it, then restarted, then died twice more as I tried to get home, then wouldn't start at all. I put the stock ECU back in and the engine cranked right up. Never really figured out what was wrong with it but I assume that something inside overheated due to current flow. You'll find a bunch out there about ECU's running rich due to bad solder joints. One quick fix is to bang on the side of it. Apparently that really works. Your 75 is the first year of the ECU's so might be the most likely to do that. If you can find a loaner or a cheap one to buy, it's always good to have a spare. Any of the 75-78 ECU's should work.

Have you opened up the idle air screw on the AFM? That's what it's for, at least for idle. I don't know how much effect it would have on 2500 RPM. But your numbers are actually really close I think, it might get you there. Take note of how many turns out it is so that you don't get lost in your adjusting, and can go back to the starting point. Then open it up until you get a miss. Then pick a spot in between and try the test again.

Turbo day. Seems like a low start, but seven bidders. Edit - there was one more bid after I posted. It sold for $8,500. https://bringatrailer.com/listing/1982-datsun-280zx-turbo-12/

Not clear what year car you're working on, and if it's California or Federal. Some have two pickups in the distributor so that timing can be changed at a certain coolant temperature, for emissions. Kind of sounds like that might have happened. Might also be combined with a bad ignition module, one circuit might be bad. If it does it again, you can disable one side and let it run on the good circuit.

75 was the first year of EFI. Might be that they changed it later. Looks like it's either on mine.

The idle speed screw uses a Phillips, but the screw head is so big that you can actually turn it by hand/fingers. It's not the idle air adjustment screw in the AFM. Leave that one alone.

Why would he need a smoke machine, or a cigar? He said it runs well once it warms up, enough to do "a lap". All that seems to be here is difficult cold starts, and some dodgy work by the PO on the wiring. Just saying, there's a risk of over-advising. There doesn't seem to be a vacuum leak problem.

Seems like the car was in pretty good shape when you got it and really just needs a few small things. Don't do anything drastic, no big changes are necessary. If it was drivable and only sat for a couple of months then many of things you'd do for a car that sat for years aren't needed. I'd focus on avoiding disasters, like burning your wiring because you have the wrong fusible links. Looks like you have that covered. Here's a simple one. Move that wire before it gets jammed in the hood latch.

Just realized that I got confused by the title. "engine fresh air ducting". Engine's got nothing to do with it, right? If a person really studied why Nissan put all that work and parts in to creating a special path for the air to the side vents...they'd probably still end up not understanding. If you ran a tube up the cowl air source, where the fresh air for the heating/cooling system enters, you'd have high pressure fresh air directly to the vents. Might not even need the large diameter because it will be pressurized while driving.

Edit - misunderstood the goal.

I would get all of your timing marks set to known correct positions then see where #1 should be and go from there. The cam lobes/compression stroke/TDC and the damper pulley mark ( which should be zero at TDC), then put wire #1 where the rotor is pointing and set the remaining five accordingly. It never hurts to reverify that things are correct. I put my wires on backward rotation (clockwise) once and the engine still started and ran, but it ran really poorly. I assume that a few cylinders still got spark close enough to make the engine go around. #1 was right for sure but I never sat down and figured out which others got spark that would work. But it "ran".

It's possible to install the oil pump drive shaft incorrectly, and that's what drives the distributor through the quill. Happens often. If you can move the plug wires so that #1 wire is where the rotor points under the cap that might do it for you. Put #1 there then install the wires in the correct order, 1-5-3-6-2-4 counterclockwise. Leave the distributor position where it is, it's correlated to the crankshaft position. It will probably start. Maybe you'll get lucky and the dead cylinder just has a stuck ring. Worth a shot.

Darn it, I tried to quote my own post but it only quoted the part I wrote. So I had to go dig around in the pile of words. This part, above, sounds like the AAR. It's the thing that looks like a torpedo on the intake manifold with the hoses running through it. If you want to get by in the short term, just turn up the idle speed screw. It will start and stay running but the idle speed will keep increasing as it warms up.

Just doing a favor for anyone else who tries to read your post. Sorry but the run on train of thought tapping on the phone texts are hard to read... (Edited - I was being an arse. Well done, Dylan.) How long have you had the car and has it ever run right?

Browsing the parts manual and came across these factory cylinder liners. Didn't realize they were a factory piece. And, even better, you can get them on Amazon. http://www.carpartsmanual.com/datsun/Z-1969-1978/engine-280z/cylinder-block/26 https://www.amazon.com/Nissan-11012-N4200-Liner-cylinder-11012N4200/dp/B01LX9V3ZK

If you've already been spinning the engine with the starter and had a few pops then starting it on 7 shouldn't do more damage. Good luck with the lash adjustment. There is something called "sunk" valves that could cause that. Not good, but it might let you get it running for a short time if you readjust. At least you'll know.

I'm going to guess that the Tonneau cover was the owner's idea, and they can't see how it really looks. Wonder what it sounds like. No offense intended if you're a member here. But it has to be noisy. And leak in the rain.

It should still start and run even with a dead cylinder.

Taking off from a dead stop. The higher the number, the easier it is. Less clutch work. If you use a ZX 3.062 with a Z 3.54, the 10.83 ratio (just multiply the numbers) is noticeably "doggy". Slow acceleration. On the other hand, some people put a 3.9 diff in their Z's to give them more zip. 3.321 x 3.9 = 12.95. Think of about 12 as what the Nissan engineers chose for the average driver. So about 11 is tolerable at the stop signs and lights, and about 13 is what you want if you're a light to light racer type.

The drawings are just representations. The hoses are smooth, the defrost tube does not shoot straight up, the front vents look different.

Nissan seemed to shoot for about 12 overall in first gear. You live in Texas so might do some 80 - 90 mph cruising, and not so many hill starts to worry about. Really depends on how you plan to use the car. These are coupe numbers. Things get weird in the 2+2 cars. Early cars 3.592 x 3.364 = 12.08 280Z's 3.321 x 3.54 = 11.76 280ZX's 3.062 x 3.9 = 11.94

It's probably just a 75-76 thing. You're hoarding the wrong cars. My 76 only had it on one side. Maybe they phased it out. 2, 1, 0.

Checking plugs and exhaust is the best way to see a rich condition. Here's another thing I learned years ago. The cylinders can lose their seal if they have surface rust and have dried out over the years. You can squirt a big shot of motor oil in through each spark plug hole so that it runs down around the rings to give you a temporary seal. A friend and I spent a day and half trying to get a 63 Bonneville started until an old farmer on a tractor came by and said "squirt some oil in the cylinders". It fired right up after we did that. It was a carbed engine but the same might apply here. Use one of those flexible nozzles or a piece of hose to get the oil up to the top of the cylinder so it runs down around the rings. If I were in your situation, I'd pull the plugs, recheck gap, squirt some oil in and let the gasoline dry out for a little while. Then squirt some starting fluid in each hole, put the plugs back in and give it a crank.

Edit - it's in the AC chapter of the FSM.

My 76 had something similar on the driver's side. It just blew air down on my feet. Can't remember if it said pull-push or not. The hose looks factory Nissan on yours.