Zed Head

I'm not positive on it. One of those things you have to check, even if you know the year. Lots happens over 40 some years. http://www.zhome.com/ZCMnL/tech/head.htm p.s. I don't think the advice about replacing an N47 head with a P79 head is good. Unless he changed pistons also.

The picture you posted is of round port headers. They should work well with your lined 77 N47 exhaust outlets, which would be considered "round". The square outline is from square holes in the gasket used. Edit - if you have an N47 head on your engine. That's the key. Can't remember exactly when the change was, it might have been internally oiled cam in 77 and lined heads in 78.

It would still be interesting to talk about how tachs work though. I learn gooder when there's a problem to solve.

Why would anyone not use it? Seems to meet the needs, and there are options. https://www.rockauto.com/en/catalog/mazda,1979,rx-7,1.1l+r2,1192227,fuel+&+air,fuel+pump,6256 It's weird that there is no option for an electric pump around the internet even though the 240Z's are wired for it. It's a market that needs to be addressed. Opportunity missed. https://www.rockauto.com/en/catalog/nissan,1973,240z,2.4l+l6,1209170,fuel+&+air,fuel+pump,6256

No, motorman7's post kind of caught me by surprise and I had to think about it for a while, and went through some edits. I see where he's coming from, he's been there since the beginning. Still shocks you though.

Actually, second edit, I can't even really see an attempt to "own" here. Seems like a total non sequitur. Oh well. I can kind of feel people getting lazy in my neighborhood, since we're in a county that's not suffering too badly. I guess the new term is "chin diaper", where people wear the face covering on their chin and only pop it up if they get close to someone. And can't seem to comprehend that just because you're drinking a coffee, it doesn't mean you can't get or transmit the virus. They're like school kids, finding ways to cheat the "rules". It's like some sort of self-correcting stupidity. Instead of continuing what works, stop and wait until things get bad again.

I'm kind of sensitized to that because my tach got all weird when I switched to a GM HEI module. My solution was a signal conditioner. Not a super fancy one like in the post I pasted but a simple condenser/capacitor on the coil negative wire. I don't know what causes the noise but the wire to the condenser wire broke once and the tach went bad again. I fixed it and it worked.

Never mind. Any response is an "own", to some perspectives.

If you live at 3,500 feet it probably changes with the weather. That would be annoying.

When I was looking at high pressure pump options I found that older Ford trucks used two pumps. One to pull from the tanks and one to pressurize the EFI system. The high pressure pump was mounted up under the driver's side firewall, and the supply pump was in the tank I think, or close to it. I don't know the specs on the supply pump but I'd assume it would be low pressure. Might be worth digging in to.

I found that these wobble head extensions, 1/2", get a good bite in the drain plug hole. It's a tough one. Once they get wallowed out it gets messy. This is the Harbor Freight version for an impact driver. No chrome helps it get a bite also. https://www.harborfreight.com/3-piece-1-2-half-inch-drive-impact-wobble-socket-extension-set-67066.html

And a free throwout bearing and sleeve! Looks like a Z shifter, not a ZX. Is that yours? Hope they knew what they were doing, it's been worked on. I'd file some new flats on the fill plug, clean up the area around the threads and squirt some penetrant on there. Then hit it with a torch or heat gun before trying to remove it, and the drain plug. Do it while it's together, it's hard to generate leverage when the cases are off. Who paints their transmission red?

He's a car guy and a consultant and likes to share his knowledge. Might be worth an email. Maybe he'll have a solution. http://www.nonlintec.com/contact.html

Here's a guy who goes way deep on how to convert an older tach to an electronic style. He had a comment about a calibration tool that was interesting. Maybe that slot is a potentiometer used to calibrate the tach (mentioned in this article). Wouldn't hurt to give it a twist back and forth and see what happens. Maybe it's corroded and not passing low current well. The material in this article is way over my head but the guy seems to know what he's talking about. Edit - I used the Hz measurement function on my multimeter a few years ago to calculate RPM from the coil output using the frequency measurement and math like he shows to see if the tach was right. Just an aside. You'll get a different number than his 1800 for our six cylinder engines. My tach was off by 200 RPM, but I never tried to calibrate it. http://www.nonlintec.com/ http://www.nonlintec.com/sprite/Sprite_Electronic_Tach.pdf

Back to how it works. The signal from the coil is just a voltage pulse. The capacitor(s) just "collect" those pulses and convert them to some sort of steady voltage that creates a magnetic field. More pulses equals stronger field. So, what components fail in a way that makes them fail sporadically, to make the needle jump then fall back like yours does? Sometimes they work and sometimes they don't. I assume that there are diodes involved also. Not an electronics guy, just like to dig as deep as I can. The above is a simpleton's guess at how the tach works. Feel free to correct. The needle movement is similar to what happens with a funky ignition module. Is it possible that the problem is the ignition module and not the tachometer? Your point about some sort of test bench is relevant. I was watching Wheeler Dealer and the guy took a tach to a guy who had a pulse generator for testing them. So they aren't that uncommon.

Looks like an adjustment. I know that the voltmeter has a similar slot that I used to adjust the needle position.

I don't really know how tachs move the needle. But I think the sweep of the needle is a continuous function, not a set of discrete steps. I found a Google thing with a nice color drawing and some words. Not sure if it's right. But, digging in to what's supposed to make the needle move, the principles behind it, might offer a clue. https://mechanics.stackexchange.com/questions/25584/how-does-the-tachometer-on-my-dashboard-actually-work

You didn't show higher RPM like 3-4000. But it looks like a physical problem might be a possibility. Sticky needle maybe, something dragging on it. Worth taking a close look at the needle movement itself. Dust, crud, rust.

So the tach needle just sits at zero, completely still, not even a quiver until engine RPM gets to about 1500, then it jumps up and sits steady at ~1500 and works normally/smoothly up to the high end? Pretty sure that a 260Z already has the 2200 ohm resistor. It looks different than the later models but it's there. Since you have the tach out you could measure resistance back to the coil negative. You could make three or four jumper extensions and run them out from the tach plug to wherever you want to set the tach for testing. Still have to start the engine but not so tedious to run a test.

I think that there's a drawing at the front of the Engine Fuel chapter of the 280Z FSM. An exploded view of all of the EFI components.

1981 280ZX Turbo. Looks good. 13,000 miles shown. https://bringatrailer.com/listing/1981-datsun-280zx-turbo-6/

I scrolled down the comments and at least three different guys have bid over one million dollars. But people are still picking over the incorrect door handles.

@Dave WM knows about reverse problems, he has some parts, and has worked on trashed transmissions. They are surprisingly durable. Reverse is a simple mechanism and can be reached from the backside of the adapter plate. Shouldn't have to remove the front case although that would let you inspect the synchros and gears. If the drainplug is in it see if it has metal stuck on it. Most yards drain the fluids though before they put them out so it might have been wiped already.

Not sure but I think that I've read about tachometer schematics somewhere in the past. I found a couple of old threads but not sure they go in to that level of detail. If you have the right meter and the capacitor still works you could measure it. Or, rearranged words, if you have the right meter and you can measure it, it still works.

Thanks for following up on the switch. It's a good tool for somebody who might have one of the aftermarket FPR's set to 38 or 40, or an AFM that runs just a bit rich, and just can't get that last bit of leanness they need to pass emissions or get a clean exhaust smell. Just short that circuit and leave it. Very useful for tuning. You kind of reported the results in the wrong thread though. Here's the post just to tie things together.