Zed Head

Earlier it was supposed that Nissan used "old parts" during the transition to the "late 1971" 240Z. If I had one I'd just use Nissan's bulletin as a check list. Actually, if I was selling one I'd do the same. It covers the issue of features, and the time and VIN just fall out of the documentation and ID tags. Just put the numbers and the features out there and let the buyers decide what they value. It would be interesting to see if there are any hybrid early/late 1971's out there. Late parts used earlier than shown (like the reversible key) or early parts used later. http://zhome.com/History/New71LateP2.htm

The question I raised is whether the timing is retarded or not, meaning that the timing would change when you switched modules. Since you would normally set the timing for just one module after installing it you wouldn't know if the retarding mechanism was in play or not. It's not about how it works but how the two different modules compare. Even the base setting, of either, might have a delay based on the internal circuitry. A timing measurement will tell.

It would be useful to know if the initial timing changes. Apparently the E12-92 retards timing by 8 degrees, but it's not clear exactly when. Probably when the engine is hot and the throttle at idle. For emissions. Retarded is cleaner. That's how the 280Z systems work, but with two pickups in the distributor. When the engine is cold the timing is kept advanced at idle to help with idle RPM. Not super clear how the ECU is involved unless it completes the ground based on engine RPM or some other condition. Anyway, in your video you can see that idle PRM are lower for the E12 module. That is what retarded timing will do, cause idle PRM to drop. So, it might be that for your tests timing is retarded by 8 degrees for the E12-92. A quick check with a timing light would answer that question. Then you'd have to decide if you want to figure out how to make the two modules match. But, the fact that it runs means that it is serving the fail-safe function, to get home if the HEI fails. p.s. here is the 280Z description for the two pickup distributors. When the circuit is open timing is retarded. Which would fit with having the E12-92 pins disconnected. I think that you'd have to run 12 volts through those extra pins to get the timing advanced to match the HEI module. Thanks for letting me fill your thread with extra stuff. An interesting puzzle.

$21,750 for a sketchy 71 240Z, modified, no ID plates visible. There is no predicting the market value of a 240Z.

The E12-92 has an extra pin that adjusts timing through a temperature switch. Might be that when you switched to it you inadvertently changed your timing. I thought that you had an E12-80. There's not really a good reason for a performance change unless the E12-92 is failing, or something else changed. p.s. some people say that you have to short the extra pin to ground or run power through to stabilize the timing. The 280ZX FSM probably shows how it works so it could be figured out. Really though, you're about ready to just move on from the old Nissan parts. I'll just pile a couple more things in here for anyone with an E12-92 in the future. Notice the idle switch and the thermo switch connected at the "IC". Somebody with electronical experience might have fun figuring out what Nissan was doing here. Last, maybe, edit - here's a zcar.com post from way back, with a reference to 240260280's friend Wayne Monteath. Apparently, it doesn't matter if the extra pins are connected or not but the question would be where your initial timing is when you switched. https://www.zcar.com/threads/e12-92-or-e12-80.116513/

This one is already up to $15,000. Funny though, the guy has been driving it with no air filters. Had the carbs rebuilt, just never put the filters back on.

This modified 71 is probably going to outdo the "early 71 Series I" 240Z. It has fender flares! Eeeewww.... https://bringatrailer.com/listing/1971-datsun-240z-231/

$12,300, RNM. Presentation is key on BAT. The seller did a not-so-good job.

I think it has something to do with the way the fuel is metered from the carburetors. With EFI the air flow is fairly precisely measured and the appropriate amount of fuel is added to balance the air. With carbs the fuel is pulled up from the float bowls and basically spilled in to the air stream. There are emulsion tubes and other things but still the fuel gets pulled up in to the air stream, more air = more fuel. If you have pulses of air from a lumpy cam (inconsistent air flow/vacuum) the fuel gets bounced up and down and accuracy/consistency is lost, plus the fuel does not stay well-atomized. Carbs work best with smooth air flow through them. EFI averages out the pulses back at the AFM or MAFS so is not as affected by a lumpy cam. That's my basic understanding.

The 70/71 is up today. Let's see what the collectors think, if any are interested. https://bringatrailer.com/listing/1970-datsun-240z-82/

You're saying that a 1973 240Z has the same value as 1970 240Z? That if you had a 73 you'd trade it straight across for a 70? Because they both say 240Z on the outside. Trying to use those played out memes will drag you in to absurdity. Be careful.

Actually, my post wasn't about the easiest way. It was about the best way to be sure both ends were correctly seated. Your bobbly speedo sounds like the cable is not fully seated and it's rubbing on the inside of the sheath. It's bound up. Or it might be that you have a bad spot on the gears. At least you know that the parts all work.

Yes and yes. There are two possible reasons that the cable is not spinning the speedo/odo parts. 1. There's enough slack in the sheath that the drive cable can get jammed up and not engage correctly. It helps to pull the inner cable out at the transmission and stick it in to its slot on the transmission end then push it back up toward the speedometer as you screw on the sheath end. At least that helped me. Apparently the speedo end seats more easily than the transmission end. I think that I had also spun the propeller shaft while I did that. I had the back wheels up. 2. The housings are different. The locking slots are oriented 180 degrees apart. The gears are offset so if you use a ZX in a Z the gears won't mesh. Look in the hole and you should be able to figure out which one you need. You can also reorient it without locking it down and see if it engages. Some people just grind a new slot in the housing when they do a transmission swap. But it's pretty easy to swap the gears too.

That's the original round style that they used on the 260Z's. The 280Z's used the rectangular one like in the drawing you posted. It looks just like the drawing. It's folded over then taped up, so it's a different shape of lump.

I had a similar thought. Or put some colors/label on the wires and the module pins. I had a module crap out on me in my garage after some engine work. Forgot to put two plug wires back on. So they do fail for various reasons, but so do the originals. I carried a spare module and the tools need to change it in the car. I also had a spare ECU behind the seat.

There's no need to get it out. Just verify that the lump is there. If the tape is unmolested you migth as well leave it. Remove all of the existing wrongness and see where you're at.

It's a lump in the taped up harness. Like a frog in a garter snake.

Av8ferg solved his problem in this thread by swapping coils. Not really clear why that worked but it did. Like SteveJ says though, the old TIU should be completely disconnected. The wire to the tachometer is a branch off of the blue wire from the engine bay. It does not run through the old module. And the 2.2 kohm resistor is in-line buried in the wiring on the way to the tachometer. You should be able to just connect the blue wire in the engine bay to the coil negative, disconnect the old module, and have everything working correctly.

Way back...

Here's some brochures from around the same time frame. https://www.gmheritagecenter.com/gm-heritage-archive/historical-brochures.html

Hope so. Seems unlikely though, doesn't it? Hopefully they fixed the root cause. Should make a huge difference. That was a lot of slop. The bonus is that you found those other problems while looking for that one.

Model years had been a thing in the States for many years before the 240Z appeared here. Any kid growing up here knew all about 55 Chevys and 67 Camaros and 72 Cuda's and 69 GTO's. You could tell a 68 GTO from a 69 by its tail lights. Same with the Chevy's. Even the tail-light lenses of the Camaros had a date stamp molded in to them. It was a point of pride to be able to tell a model year at a glance when you saw a cool car. HS30 seems to be saying that other countries don't define cars by year. Apparently a "model" exists as an entity through many years and changes are implemented as needed or desired, at any time during the model's production. I did not realize that the States is the only place that defines cars by model year. Interesting fact, I learned something about the rest of the world. Nissan did catch on to the model year nomenclature by 1973, apparently. They changed the wording of the Foreword in the Service Manuals. Here's 72 and 73.

Any chance that the noise is actually from a failed differential or mustache bar mount/bushing? The diffs are inherently noisy. If you have any spare differentials you could swap one in and see if there's a change. Or take a hard look at the mounting areas. On deceleration the diff nose is pushed down. And the metal edge of the diff mount is very close to the crossmember. It's easy to imagine that the edge of the mount contacts the crossmember on deceleration. Borrowed a picture from somebody's web site.

Even that link you posted isn't working. It's a shame that they kept taking people's money for so long. I wonder how many people will get screwed. https://whiteheadperformance.com/