Zed Head

Are you running the 1977 ignition system? 1977 was still using the weak electronic system. Your cam is going to cause variation in the gasoline/air ratio, especially if you try to maintain a low idle RPM, plus the batch fire nature of the old EFI system also causes variation across the cylinder. A better ignition system might help.

Didn't know you were running a lumpy cam. That thread from zcar.com is interesting. A lot of what would be considered bad advice on how to get the 260 cam to run "right". Fiddle with the AFM, run direct vacuum advance, adjust the TVS so it's off-idle. wangsman's version of "runs great" seems to be pulling hard to 6000 RPM. Your issue is at idle. You can tell from the comments that some of the opinion might be more of an "I made it work" view. I'll bet their cars smelled like raw gas at idle. No offense to the two guys that said it can run just fine with the lumpy cam, but that's how the brain works. We probably all have memories of the guy in high school that thought his car was fantastic but nobody wanted to ride with him. @Jeff G 78 is one of the guys in the thread. He knows a bit about how to get these engines to "run right". It will be entertaining to see where you end up. How are you going to write a guide if you take it to a tuning shop? What goals will you set for the tuners? Today's tuners only know how to use computers to tune automotive computers (I just saw one of those car repair videos that the guy titled "millenial vs. carburetor" or something like that) . Take special note of the looks on their faces when they see what you're working with. Should be fun.

From up north - http://www.atlanticz.ca/zclub/techtips/tempsensorpot/index.html

The bucking sounds like the typical lean mixture problem. Solved with the potentiometer in the coolant temperature circuit to richen things up.

Some people have problems with Eibach springs. It seems to vary, almost like the springs are coming from different sources. The common problem is that the front ends up higher than the back. Others have no problems.

I'm going to guess that the jolt was a ball cage/retainer on one of the adapter plate bearings. People often find pieces of the retainer when they do a fluid change. The transmissions seem to just keep going though, it's amazing how destroyed they can look but still do just fine when new parts are installed. Draining the fluid will probably tell you something. Look for metal shavings and flat pieces of metal. https://www.researchgate.net/figure/Main-parts-of-ball-bearing_fig1_289540744

You guys are reminding me of something I see on some of these youtube repair videos. You can see proper voltage but it's best to put a load on the circuit to make sure the current is there. The guys that seem to know make up their own test lights with a headlight bulb. A cruddy connection might show proper voltage, especially with today's digital meters. But it disappears when a load is on.

But you do bring up a good point about the grounding part of the circuit. You could have power but no ground. You can measure voltage at the ECU connector also. That will test the whole circuit. If you have voltage there then your theory about the ECU fits. Then you can get out your magnifying glass and check the trace back to the transistor.

Did you disconnect all of the injectors before you measured voltage at the injector plug? And did you measure both pins of the injector plug? You are correct about power and the ECU grounds. But the ECU grounds several injectors at the same time, in two separate groups. If you left the other injectors plugged in and saw voltage on one pin it would be because the injectors are wired in parallel as CO explained long ago. You need to unplug all six injectors before checking for voltage. Actually, that should have been the first suggestion, before digging in to the dropping resistors. Unplug all six to break up the parallel circuit, turn on the key, and measure voltage at each pin of each injector plug. That will tell if #1 is getting power. You should see battery voltage on one pin of each plug.

Looks like they are not color coded. So, your best bet is to unplug them all and confirm continuity for each power wire to each injector. Then check the wires in the dropping resistor itself if you find that all injectors have continuity. You'll have to remove the resistors for that. The problem would be either in the dropping resistor assembly itself or in the harness on the way to the injector plug. Edit - just noticed that #1 should come from the resistor with five wires. Just keep narrowing things down... If the drawing is correct you can even tell which pin is #1 by its position.

I would unplug the dropping resistors (you might be able to do it without removing the resistor, can't remember), then check continuity to the injector #1 plug from the resistor plug. I don't know if the wires at the dropping resistor are color coded or not.

You're making good progress. You probably have a bad connection somewhere in the wiring harness. The most likely spot is at the dropping resistors, which are underneath and behind the washer fluid jug. Some screws hold them in. I would go there and take a look. That's where the power passes. You can check voltage in to the resistors at the plug too. Several injectors are fed through each resistor, so check each wire carefully. Edit, actually voltage in to the resistor would affect several injectors. Focus on voltage out.

Cliff's method works. Another is the bolt pattern. Nissan did not drill theirs for both. 225 is 6 evenly spaced bolt holes, 240 is 3 sets of 3. 225 240

Hey! 39 / 11 = 3.54. That's what all of the 280Z R200's are. I went through the whole thing of trying to take out only the parts I was working on when I first did my diff, prying and torqueing bits and pieces. It was a pain. If I recall correctly, I ended up later just removing the mustache bar end nuts and the front crossmember and dropping all three pieces down as an assembly. The mustache bar makes a good handle for balancing and you can just drop everything straight down. It works for assembly too.

It does look more like injector alone. You can do a lot before swapping injectors. You can measure resistance across the pins. Should be about 2.5 ohms. You can connect a 9 volt battery across the terminals, with a fuel pressure gauge connected. You should hear it click and see pressure drop as the fuel is squirted in to the cylinder. You can put a noid light in the injector plug and see if it flashes while the engine is running. If you had a bad vacuum leak at the injector you might also get a lean misfire. You could check that by squirting starting fluid or carb cleaner at the injector gasket while the engine is running. Should get some fire then if there's a leak. That might explain why you're hearing the right noises and seeing sparks but not getting fire.

I noticed on my engines that #1 seems to run lean, the plugs are always whiter than the others. I think it has to do with air flow, #1 must get more air. So if your system is tuned to the edge of lean, #1 might be too lean to fire at idle. Just a guess. You could adjust the idle air screw to richen things up. Screwing it in will divert more air past the vane, adding fuel. You could also pop the black cover and move the counterweight. The dead cylinder might be only happening at idle. That might explain why the plug porcelain is dark, indicating combustion at some time. A dead cylinder with a new plug should be "like-new" white.

The 1971 240SX. Kind of early for it... https://en.wikipedia.org/wiki/Nissan_240SX Those cars are pretty far out there. Probably nice and dry. https://goo.gl/maps/FY845t1sCBXpqpXT7

There is a pretty rare vehicle in that collection.

I think that it already has a draw-through turbo. Don't know much about it but I found an old thread showing a similar setup on an L4. Edit - it's in @Racer X 's neighborhood. He probably knows about those old turbo kits too. https://ratsun.net/topic/57895-datsun-510-l20-looking-for-turbo-kit-for-it/

Here's a post from the middle of the last conversation. It's a hybrid 240/280. I never did find out what the firewall VIN was. I just noticed that it even has the 280Z air filter and ductwork (edit - actually I did notice that before...). And the charcoal canister.

The 1972 280Z (we had much discussion about this one in the past. Can't remember what we decided) is still up on the Beverly Hills site. Looks like new pictures. Like they're daring somebody to buy it. https://www.beverlyhillscarclub.com/1972-datsun-240z-c-11820.htm

The purple filter cover is a nice touch.

I Reported the new member's post. That should do it.

Might be the owner's Supra.