Zed Head

It's not a "rev limiter" it's a deficiency in the quality of the spark, according to Vizard. I remembered that I had found and copied some pages from an old article by Vizard and managed to find them again. His whole issue was that the stock HEI system's spark quality, aka voltage, dropped off too soon (for his desires). As I recall now, the reason it bothered me was that he was bashing the system based on race engine needs. Typical bench racer stuff. (p.s. actually, in looking at what he wrote, I realize that what's bothered me over the years is how this limitation shown by Vizard has been spread around the gear head world as gospel, even though it's basically nonsense for a typical car hobbyist.) In looking at the pages I even see that his "limit" was actually 5,500 RPM. His recommendations are for ways to get the RPM spark quality up to 7, 8, or 9,000 RPM. Here are a few excerpts from those pages.

Yours does not look the picture in post #1 or on MSA's web site. You said that you bought them from "Z Car"? Is that a typo? It's Motor Sport Auto or theztore.com. There's no projection on the bottom in their pictures. The part number seems different too, 29-2021. Not sure if that has meaning.

The other thread seems to be gone but so is @siteunseen 's post that was in it. Oops. The test for the sporadically bad ECU problem is to bang on it. I don't think that it will show up from the Nissan test procedures. It might show up on a scope if you had one. That's the big thing at the small repair shops on the Youtube channels, they have scopes that they can take with them as they go for test drives. Pretty cool, but takes some money and know-how.

The richness and erratic running kind of fit what's been reported for a failing ECU. I had one fail as I was testing it, but it just died completely as I was road-testing, then restarted after a few seconds. It did this about three times before it wouldn't restart as I tried to get home. I was about a mile from home. The exhaust smelled like fuel as I tried to restart it at the end. I ran home and got the original and the engine started right back up and was fine after that. Anyway, short answer, people have had luck diagnosing it by banging on the side of the ECU or wiggling the wires to it as the problem is happening. If the problem clears up then you know it's in the ECU. Apparently the problem is caused by broken solder joints. People have had luck reflowing them, I didn't try on mine. p.s. since the "problem" is fairly common it can be defined as an "issue". That's just how words work. "The issue under discussion is the common EFI ECU problem". https://dictionary.cambridge.org/us/dictionary/english/issue

Not sure how a light emitting DIODE can not be polarity sensitive. It's part of the definition isn't it?

Not really sure what you're saying here. There is no flasher on the tachometer bulb circuit that needs current to work properly. Id' guess that you have a contact problem.

That would be one question. Then there's the supposed 4500 (V8) RPM limit for the HEI module (which would be 6000 RPM for a 6 cylinder). Others might be "does the broken magnet in a ZX distributor cause it to stop working?", "what difference is seen between a 4.5 amp HEI module with a 0.6 ohm coil (factory setup) versus a 7 amp HEI module (Pertronix and others) and 3.0 ohm coil?", ... and on and on. Ideally, I think, you'd be driving a real distributor at a known high RPM. Then there are the other odd questions, like "why does a GM HEI module work as a replacement for a 280ZX turbo ECCS "ignitor" (power transistor) when there is no zero-crossing?". Is the 123 ignition module current-limiting? Is an old Ford ignition module similar in function to the GM HEI module even though it's designed for a Hall Effect signal? You could also get in to the heads of the engineers and explain why they changed the triggering mechanism from the single reluctor to the six point reluctor. You touched on it in a past post as giving a higher cranking voltage. I thought that it might also give more consistent timing cylinder to cylinder, because it averages all of the points in to one voltage pulse. People have found that the 280Z type reluctor wheels have enough variation between the points that the timing varies between cylinders. On the high performance engines it can cause problems. It's all interesting.

I wonder which circuit had the effect.

The exhaust system is bolted to the transmission. Seems possible. "clang" is not much to work with. There is also the bushing in the tail shaft housing. You might grab the propeller shaft and see if it's loose.

I see only one start. Have there been more? The conductive part of the relay is affected mostly by the contact points. Not really clear what you cleaned up. Did you take any pictures? And you reported zero after, but no number before. How much resistance? And, to be be picky, the relay would have to be actuated in order to measure the resistance to the components that get the power. Through the relay circuit. Just saying, it's hard to tell what you did. (p.s. it's "lo".)

Could you set up a test bench to measure module performance against RPM? Look for timing changes and/or reduced charging time. I think that that is the issue that Vizard had with the GM HEI module. As I recall he proposed it but never actually showed that it happened. I think I've written about it in the past. You could even blow up some modules by leaving them ungrounded or with poor cooling. Only $25 / experiment!

Are you taking questions or will you just be adding things as you explore? You had more in Av8's thread, with the Z wave form, compared to the ZX. Still wondering why this forum doesn't have Stickies. So many good discussions are buried back in the past.

Official Nissan material or something else? Do you have a reference? I'm pretty sure that the injectors do boil dry at times, it fits with the heat soak/hot start problem.

There are 38 posts in this thread so I might have mentioned it already. But I modified my 76 filler neck to take an unleaded nozzle without falling out. Not clear what you did but that would be an improvement (I think). You cannot hang a nozzle from the huge 76 opening. You have to stand there and hold it.

I have many questions. Can't wait. Maybe some Pertronix or 123 modules can be looked at, to compare. Or David Vizard's 4500 RPM limit (V8) for the HEI module. Many unanswered questions floating around out there.

The fact that the engineers must have designed algorithms that converted degrees to time (very small intervals of time) in to the ignition system has been in the back of my brain since I started learning about them. I wonder how accurate it could actually be. And it must be more accurate at low RPM. I wonder if weird stuff happens if you use the retard setting at high RPM. It would be interesting to compare high PRM timing between the two modules. I've always read that the GM HEI module used a positive crossing trigger. The rising edge. But, another thing that's been in the back of my mind is that silicon transistors switch at 0.7 volts, apparently (not a semiconductor expert). People use the GM HEI module in place if the "ignitor" on the 280ZX Turbo ECCS ignition systems. Which should never go negative, it should just have a zero to 5 volt square wave. Maybe the HEI module has circuitry that works on a zero transition though. Not my field. If it has to cross zero it should not work in the ZX ECCS system. Anyway, it was fun to learn something new about these two modules. Lots of interesting stuff about the GM HEI modules in the Megasquirt world. http://www.megamanual.com/ms2/GM_7pinHEI.htm

That is a weird one. It's not really what was suggested, which was old parts being used up during the transition. That one has parts that are not supposed to be in use yet. Any chance somebody just wanted the "improved" parts and had them switched later?

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/