FastWoman

I wired a potentiometer in series with the #13 wire/connector to my ECU. The potentiometer is mounted just underneath the dash. It is a 20-turn variety that I heat-shrunk to the side of an electrical connector. Now I can adjust my mixture very accurately with the turn a very tiny screw. Details are in post #66 of this thread: http://www.classiczcars.com/forums/showthread.php?40234-Purs-like-a-kitten/page3&highlight=purs+like+a+kitten

^^^^ Good point! I'd frankly buy new injectors if you can afford it -- about $150 for the set: http://www.ebay.com/itm/75-76-77-78-79-80-81-82-83-Datsun-280Z-Fuel-Injectors-/160661473384?pt=Motors_Car_Truck_Parts_Accessories&fits=Model%3A280Z&vxp=mtr&hash=item25682b8868 I'm running this type of injector, and it seems to do just fine.

Well, there are a few of us on this list whose electronics have drifted in their calibration over the decades. On mine, the injector pulses had gotten too short, resulting in a lean running condition. I determined this only by first going through every inch of my EFI system with a fine-tooth comb and setting everything right, including the AFM. When it still didn't run right, the unavoidable conclusion was that the ECU needed tweaking. I accomplished this by altering the resistance of the coolant temp sensor circuit. This is the most important sensor to the ECU, aside from the AFM itself. Its resistance impacts the pulse duration the same way under all operating conditions. So my advice to you is to make sure everything is operating correctly (no leaks, proper timing, etc.) and then to adjust the CTS resistance to maximize your engine vacuum (to around 19 in Hg). To determine whether the engine is running rich or lean, you can remove the cover plate to the AFM and tweak the mechanism with your finger. If vacuum is maximized when you open the vane a bit further, your engine is running lean and needs more fuel. Remedy this by adding resistance to the CTS circuit (with a potentiometer in series with the CTS). If you find the opposite, that vacuum is maximized when you tweak the AFM a bit more closed, your engine needs less fuel. You would remedy this by wiring a potentiometer in parallel with the CTS. Then adjust the potentiometer to maximize engine vacuum and performance.

If you have a bad connection, the car might start, but it will run really rich, with black smoke out the exhaust. If the sensor is shorted, the engine will run very lean. I don't know whether it would start that way. The best way to check your sensor and connections together is at the ECU plug. As I recall, you need to check resistance between pin 13 and ground. Try starting the engine with the fuel/air mixture modifications I suggested, and see if either one gets the engine running any better. Of course this is just for diagnostic purposes.

Is it a steady, "chug, chug, chug" sort of rough, that would suggest a cylinder or two that consistently isn't firing? Or do you have a random, irregular miss? Try richening the mixture by pulling the vacuum hose off of the fuel pressure regulator. Block the hose to seal the vacuum leak. Better or worse? Try leaning the mixture by pulling off the vacuum hose to the HVAC system (next to the brake booster vacuum hose). Better or worse?

If you physically removed the coil, you would have to jump a spark between a wire hooked to the coil's output and the coil's mounting base.

Check your fuel pressure when your engine dies. When my fuel pump was failing, it would generate adequate pressure until it heated up. Then it would fail... and then be normal again after it cooled down. Also check the wiring harness connection just inside the passenger firewall. The fuel pump connection is inadequate and can arc and fail. I fixed mine by snipping the wire out and connecting with a bullet connector.

All I can contribute here is that fuel pressure retention is not a problem on my car, as I have a primer switch I hit to bring fuel pressure up to spec before ever turning the key. My system is pretty tight anyway, and it holds pressure. It's mostly a quirky habit of mine to prime before starting, so I suppose that's why I still do it. (That's what I need to do to start our boat.) The car starts fine even after several days without hitting the primer switch. Anyway, cold starts are no problem. Warm starts (after sitting 20-30 min) are rough. Zed, I think your theory about sticking parts could be meritorious; however, the little needle is metal, and the body is plastic. The plastic should expand more than the metal when hot, so tolerances should get sloppier. Besides that, I've never had problems with my injectors in a hot engine. The problem is only with a warm restart -- and not right away, but only after sitting 20-30 min -- and not after sitting for a couple of hours or even several days. The best theory I've heard, that many people insist is impossible, is that fuel is vaporizing inside the hot injector, so that fuel vapor, rather than liquid fuel, is being injected. less fuel can be injected as a vapor than as a liquid (under the same pressure), hence the lean running. As a student of physics and physical chemistry at one time, I can assure everyone that given a high enough temperature, gasoline WILL vaporize at [pick your pressure] psi. The only question is what temperature and what pressure, and that depends on the gasoline formulation, which varies seasonally.

The only parts of my harness system that have deteriorated are (or were) the engine harness connectors (rotted) and a heater fan motor connector (whose spade connectors fell out). All were replaceable. The Bosch-style engine harness connectors are available on ebay ("280z injector connectors").

The first thing to do is to measure across 39 and 36 with the AFM unplugged. Then measure across the plug end. That will tell you where you're getting conductivity. It sounds like your contacts aren't actually closing, or else you'd get a zero'ish reading. Perhaps a switch part is bent? What happens if you gently nudge the contact with the tip of a pen?

All of the ICs were proprietary, never available to mere mortals, certainly not avalable to anyone now. Exactly. When the ECU wakes up, it starts counting sparks, but it has no idea which spark goes with which cylinder.

Some threads need to drift! Blue, you need an ozone generator (about $150 on ebay -- we have one like 380399465104). Ozone will kill ANY odor. I've successfully killed the odor of much worse than your 12 mummified rodents, but possibly not worse than a dead cat. I'm not so sure about the bag of volcanic rock. We just bought a house with a musty smelling shed. The PO swore we needed to try a bag of this miraculous volcanic rock, bought us one, and hung it up. It's been hanging in there for a month, and the shed smells exactly the same to MY nose.

I think I would be offended if a stranger walked up behind me and grasped my shoulder for balance while removing a shoe to shake out a pebble. I wouldn't consider my car much different -- even if it's my junky old Saturn with a beautiful patina of road grime. It's just bad manners. However, if a stranger taps me on the shoulder to tell me my shoe lace is untied, that's entirely different.

Ah! Your problem is the ripped boots -- at least the one from the AFM to the throttle body. It's letting unmetered air enter the intake, so less fuel is delivered. When you start your engine, the fuel/air mixture is richened. When the engine warms up, the mix leans out to normal. Rather, it would be normal if you didn't have a leaky boot. In your case, the mix probably starts somewhat normal and becomes lean. Try Courtesy Nissan for the boots. I think they're still available. You can also find them on Ebay.

FAIW, the "can transistors with the flying saucer heat sinks" are analog integrated circuits, just unusually packaged. Back in the day, ICs didn't have heat sinks on their backs like they do today. In fact ICs were very new, most of them plastic-packaged, without heat sinks. I believe the LM78xx voltage regulators were the first ICs to have heat sinks in the late 70's. They were bolt-down tabs -- same design as on some more recent power transistors. The flying saucer around a can was an unusual packaging/cooling approach for an IC, but I don't think there was much of a "usual" back then. The thing about canned transistors from the 60's and 70's was that the cooling oil would leak out. I wonder whether our canned ICs have the same problem. If so, it could contribute to semiconductor breakdown, leading to some of the old age "drift" problems some of us experience. If I were you, I'd just fix what's there. It sounds like your system is pretty solid. If you're running a bit rich, it might be the coolant temp sensor or the throttle position switch. Just track it down. Idle speed is adjusted with the big screw on the throttle body. The stinkiness is probably just a consequence of your not having a catalytic converter.

Teflon tape doesn't conduct, but it always gets shredded when the threads are screwed together, so I don't think it's an issue. I've never seen Tefon tape actually insulate a connection. The rough hot-restart is a common and controversial issue that's the source of much speculation. Many point to fuel vaporization, especially in the hot injectors, sometimes exacerbated by too volatile a mix of fuel. Others point to various leakages in the fuel system.

^^^^ great idea!

Performance? Probably a bit better than carbs. One of the bigger issues with the L-Jetronic system is the flow-restrictive airflow meter. A more modern EFI system with a MAP sensor or hot wire anenometer is going to be less flow restrictive. The same sort of flow restriction exists in the workings of any carburetor. As far as I can tell from my computer, a more modern EFI does increase efficiency and performance over the L-Jet, but the improvement is not so great as to justify the effort (in many people's view). I'm told that our L28 engines, with their fixed-timing 2-valve/cyl architecture, are simply not going to deliver 30 mpg performance like a modern engine. I don't know whether that's true. In my own experience, the properly functioning L-Jet functions as well as the best carburetors I've ever owned and far better than the other 80% of carburetors I've owned, with the possible exception of hot restarts. Could it be better? Sure. However, it's still pretty good.

I bought a spare for $20 off of eBay. I guess that was a pretty lucky find. Here's one for $100, but you might try offering $50: http://www.ebay.com/itm/ECU-used-1975-1977-280Z-/120756404307?pt=Motors_Car_Truck_Parts_Accessories&fits=Model%3A280Z%7CYear%3A1976&vxp=mtr&hash=item1c1da48053 If you're patient, you might find one cheaper. I don't know all the pin numbers from memory, but I'm presuming you're saying everything checks. Just the same, I'll offer the following thoughts: If you have these essential elements... +12 and ground to the ECU Spark Continuity from the coil to #1 of the ECU A +12 reading on each of the injector wires (measured at ECU plug) Healthy connections for all of the above A marginally working ECU ... then you should get at least a base pulse to the injectors. Be certain to check the connections to and from the drop resistor assembly, located beneath the brake master cylinder. Current to the injectors passes through that assembly.

Horseman, if he doesn't block the unused ports, he'll be blowing raw fuel and air into the exhaust. Also what should make the motor run slowly is to remove all the possible lumpiness, preserving the momentum from the #1 power stroke to deliver it into the next compression stroke -- or at least so goes my theory.

I've been away from my computer... sorry. Sounds like you're on the right track. FAIW, the big, one-cylinder marine engines that were used by watermen around here were all started by hand. They would simply turn the engine's huge flywheel to a sweet spot just past TDC, power up the ignition coil, and bang -- it would start running. If you convert to fewer cylinders, don't forget to block off their intake ports -- at least the #2 and #3.

Have you read your spark plugs? That's the best way to look for differences between cylinders.

Check that there's continuity between the (-) post of your ignition coil and the #1 contact on your EFI plug. That provides the signal that increments the ECU (which fires an injector pulse once for every 3 sparks).

Well, it would be Z related if it's your Z that is wishing all its siblings a happy new year. So my Z says, "Beep beep!" back to yours. Happy new year from me too.

You can also use a bolt extractor bit. Just drill a little hole in the head, insert the bit, and turn. (It's not as easy as that, but if you have the bolt extractor set and not the dremel tool...)