FastWoman

Me too. I don't know whether it's true, and I'm sure I will be corrected by somebody on this, but the badge "Datsun" was supposedly used to avoid embarrassment to the Nissan Corp., should the line of automobiles become a complete flop. Is this happening all over again with this budget line of cars for emerging markets? :disappoin

As you're someone who pays someone to do restoration work for you, rather than someone who tinkers with the car on weekends herself, you'd be far better off to buy a Z in excellent condition that someone else has already gone through the pains and expense of restoring. You simply can't sell these cars (yet?) for what it costs to put them in pristine condition. You're better off letting someone else take a small loss and buying the car (almost) exactly the way you want it. You might spend anywhere between $5k - $15k for a nice running Z. Plan on spending a bit more after that to get the "perfectly" running engine and drivetrain straight, because I swear they are never really sold that way, irrespective of how pretty the car is.

I've had luck using the approach Olzed suggests. You can drive an awl between the bolt and the threads where the metal on the bolt is thin (i.e. where you started drilling into the threads). This will mess up the threads, but it will collapse the bolt in on itself. Once you've partially collapsed the bolt, you stand a chance of working it loose and extracting it from the hole. Once the offending metal is removed, you can clean up the threads with a tap, and they're not too much worse for the wear. Of course this works better with a well centered hole (and thin walls all around), but it also works with off center ones.

... and just like the 1931 Bugatti Royale Kellner Coupe that was sold for $8,700,000 in 1987, this fine vehicle has exactly four rubber tires. Just think, you don't have to pay almost $10 million -- or a million and a quarter -- or even $70 grand -- for such an excellent ride. You can buy my Z for a mere $69,000.

I think I've gotten about as intimate with the L28 EFI as anyone here, and I agree with others that I wouldn't use the old L-Jet system. It's not that I don't think it would work appropriately for the L24. In fact the L-Jet should make the transition between engines better than a modern MAP sensor system. Rather, it's because the old L-Jet system is going to perform as an antiquated and delapidated piece of junk. The ONLY reason I have the original L-Jet system in my 280Z is for its originality. Unlike most people here, I have fond memories of the L-Jet as my very first fuel injection system (on a different Z), and I want to preserve mine as a working example of that technology. However, if I were going non-stock, I'd retrofit with a modern (e.g. MegaSquirt) system. It would make far more sense. Here's mine, BTW -- stock system, nonstock colors ...

Sorry to take so long to get back to you. It sounds like you're gettings things fairly straight anyway. In response to your questions: I guess I haven't been as buried in the details of this thread as I should be. I've just been preoccupied with other things and check in briefly when I have time (like this morning -- only a few spare minutes). Anyway, I thought you were running lean. I'll caution you that your plugs and your exhaust can possibly lie to you about whether you're rich or lean. When the mixture is EXTREMELY lean, you'll get a very slow, incomplete combustion, which will give you excess hydrocarbons, CO (I think), and carbon-fouled plugs. I know because that was the condition of my own engine. IMO, the very best way to assess the mixture being delivered to your engine is to finger the AFM vane (i.e. with the engine running and the AFM cover removed). As I recall, you've done that. FAIW, you can use the potentiometer method to lean out the mixture a bit if you wire the potentiometer in parallel (rather than in series) with the CTS. In that case, 5k would cause the engine to run roughly as is, and any adjustment in the 0k direction would lean out the mixture. There's no difference as long as airflow hasn't pegged out the AFM. However, if you loosen the clockspring to correct a lean-running condition, the AFM will peg out at a lower airflow rate, and beyond that, the engine will run lean. If you're tightening it to correct a rich running condition, it will take more airflow to peg out the AFM, and I suppose that could result in rich running at high airflow rates (perhaps?). I like to keep the AFM calibrated for the correct mechanical response and then to make the electronic response work from there.

RCB, to wire the potentiometer (also called a variable resistor) in series, you would partially unwrap the EFI harness near the ECU, cut the #13 wire to the ECU plug, and connect in the potentiometer between the two wire ends. I would suggest soldering the connections and then insulating with heat shrink tubing. You can find "how to solder" videos on YouTube. It's easy. As an alternative, you can connect the potentiometer in series with your CTS under the hood (not my favorite installation place). Just connect a male and female bullet connector to the two contacts on the potentiometer (see below), and plug the assembly in series with the bullet connectors on EITHER SIDE of the CTS connector. As to which two of the three connectors on the potentiometer to wire: You can determine this by trial and error before you ever connect the thing up. Simply adjust the potentiometer to anywhere in the middle of the adjustment range. Then measure the resistance across any pair of connectors on the potentiometer. If you measure 5 kOhm (on a 5 kOhm potentiometer), you have identified the only connector pair that won't work for what you're doing. Pick a different pair. Identify which direction of adjustment INCREASES the resistance across the connectors. This is the direction of adjustment that would make your fuel/air mixture richer. Now adjust the potentiometer's resistance all the way to zero (leanest possible adjustment). You may wire the potentiometer to the clipped wire ends in either direction -- as long as one wire goes to one connector, and one wire goes to the other. Now insulate it all up, and start your engine. With the potentiometer adjusted to zero, it will run as it did. Now adjusting the potentiometer to higher and higher resistances, you will be richening your mixture. That's it! It's actually very easy.

Blue, I could be wrong (wouldn't be the first time), but I suspect the ECU circuitry would be TTL and would therefore run off of a 5V internal voltage. If this is true, I suspect anything over 6 or 7 volts would safely run it. RCB, you say you have 32 psi fuel pressure and 18.5 in Hg vacuum at idle. These measurements don't agree. Either that, or your fuel pressure is too high. I suspect your gauges aren't quite accurate. IIRC, fuel pressure w/o vacuum should be 36.3, and with a 19 in vacuum (approx 9 psi), that should drop to 27.3 psi. A 4.3 psi drop would correspond to roughly a 9 in Hg vacuum, which perhaps sounds more likely. Anyway, these numbers don't agree. Have you tried adding resistance to the coolant temp sensor circuit yet?

I understand, and yes, it sounds logical. I didn't realize you had a problem with the first 10-15 sec of a cold start.

Here's my totally wonky idea: How about an electronic circuit that would literally "buzz" the injectors to shake any fuel vapor bubbles out of the tip of the injector? I'm thinking maybe of a warm-start push-button. The circuit would need to drive a bank of power transistors that would ground the injectors. It could be wired safely in parallel with the ECU wiring to the injectors. There might be a bit of smoke out the exhaust on that first fireup, but then the engine would run smoothly.

RCB, you should probably check the static pressure of your fuel pump, both cold and after warm-up. The way you do it is to disconnect the line from your fuel filter to your fuel rail and to attach your gauge there (i.e. with the fuel rail completely disconnected, and with the fuel line dead-ending into the gauge). You should get at least 45 psi, as I recall. When my fuel pump failed, its failure was apparent only after it had been running for maybe 30 min. Then the pressure would start sagging. You should also check to see how much volume your pump puts out. Reconnect the fuel rail, and connect up a clear vinyl hose to your FPR's return outlet. Put the other end of the hose in the tank's filler neck. Now run the pump, and see how much fuel flows through the hose. In the case of my own pump, fuel flow would start out OK and then slow down as the pump warmed up. Return flow would eventually come to a halt at the regulated pressure, and then the pressure would slowly sag from there (i.e. still with no return fuel flow). Make certain your electrical connections to your fuel pump are solid. At one time I had a crusty and arcing connection in my main harness firewall connector (passenger side). I eventually snipped out the wire and reconnected with a bullet connector. I doubt your CSV could result in a lean condition, or perhaps I'm misunderstanding. It's only active for a very short time (assuming the thermotime switch works properly), so it is not responsible for much beyond the start. It's true that it can stick open, but when that happens, the mixture will be rich. Of course if it sticks closed, it can result in a hard start condition. FAIW, I would calibrate the AFM's clockspring via Blue's method, so that vane movement is correct to the airflow through the device. Forget about mixture. Then add the potentiometer and calibrate O2 on the dyno using THAT adjustment.

Pin 1 is the signal from the negative side of the coil.

Et tu, Eric!

Black interior plastic? Is it in good shape? Could you give me a price for all of it -- A pillars, trim pieces below dash, hatch area plastic? Also is the rear bumper in good shape? (I might be the only person on the planet interested in a decent chrome park bench! )

It's a common, and somewhat mysterious, issue with the EFI Z. Do a search for "hot restart," and you should find more than enough speculation. In fact there's a new thread by Zed Head, in which he suggests it might be the coolant temp circuit that overheats when sitting there, causing a lean running condition. Many have speculated the problem is from fuel vaporization in the hot injectors. (Fresh fuel is then required to cool them.) Some say it's vaporization in the fuel rail, somewhat like a vapor lock condition in a carb'ed engine, but that theory is vigorously disputed and probably without too much merit. The short story is that we don't really know, even after roughly 35 years.

... or add a normally closed pushbutton in series with the CTS sensor. If you push it, fuel will come.

^^^ Not a bad idea, Obvious! Zed, the only thing that makes me doubt your theory is that my stumbling problem is resolved immediately by my taking off down the road with my foot liberally on the gas. I only have to go a few hundred feet. I doubt that's enough time to change the CTS temperature much. OTOH, the stumbling will continue for at least a couple of min (?) if I just sit there with the car idling. I think the difference is gas flow through the injectors. FAIW, your stumbling issue and mine might actually be different. I'm pretty sure my engine isn't running (as?) lean on a hot start. At least I'm not getting any intake pops.

Wow, it would be tempting to buy the new distributor just "because." FAIW, you can get a lifetime-warranted, rebuilt distributor from autozone for about $100. The lifetime warranty is important, because the design of the breaker plate mechanism isn't all that great, and you will likely USE the warranty at some point. I'd be skeptical of a used and non-rebuilt part, because of the breaker plate issue. (It sticks and jams as the bearings rust and fall out.)

My '78 has the backfire valve, and the '77, being similar to the '78 in so many ways, would probably have it too. (Blue would be a better authority on this.) I know the '76 has it and that the '75 does not. I picked up a spare AFM that was apparently for a 1980 ZX, and if I recall correctly (because it's in a box in the attic), it was cheapened to omit the valve. Perhaps the ZX'es had some other backfire relief provisions. Blue, a backfire from lean running is enough to damage the '75 vane too. I remember fixing mine as a college kid by tapping it out with a claw hammer. RCB, I would check out two additional things on your AFM. First, make certain there is no friction in the vane. You can do that during your beer-can calibration. When you have the beer can w/water hanging from the vane, gently lift the can with your finger, and slowly release pressure. Note where the vane settles. Then gently depress the can with your finger and slowly release pressure. The vane should settle in approximately the same place. In reality, you might have SOME friction, but I would guess if the stickiness only accounts for 1/8" in variance or less, you're probably OK. BTW, WD40 is good for working out old oil in the bearing. Then find a *mechanical* multimeter (i.e. with a needle movement). Attach one lead to the wiper contact, and one lead to either end of the potentiometer trace. With the meter measuring resistance (ohms), *slowly* move the vane back and forth, and look for smooth needle movement. There should be no sudden jumps that would indicate a poor wiper contact or dirty trace. You can use WD40 to clean the trace. Gently mop up any excess with a paper towel.

Good for you! You'll eventually prevail. The anti-backfire valve is in '76 and forward, as far as I'm aware. I had a '75 as a college kid and envied the '76 design, because occasional backfires would bend my AFM's vane. I came in on the thread rather late and don't have time to re-read the whole thing. However, in my experience on my '78, I have some unpredictability in idle from an AAR that really needs replacement. (I've nursed it along, but it seems to be more trouble than it's worth.) I find my idle gets somewhat irratic if my fuel/air mixture is a bit too lean. I suspect that's because it's easier for an engine to run with too rich than too lean a mixture, and small changes in RPM around idle could cause variations in mixture (e.g. if there's any hysteresis in AFM movement). If the mixture is just a tiny bit rich, the mixture variations are relatively less consequential. Just speculation.

Shouldn't be any moisture problems, as it's a sealed module. I didn't really know whether there would be any heat issues, so I threw in the heat sink by default. Better safe than sorry.

120k isn't really many miles on an engine. Mine has 170. That said, your compression numbers are a bit uneven -- not enough to indicate a problem, but a bit uneven still. I'm a bit confused as to where the AFM was adjusted, how it's adjusted now, and how that relates to how it came out of the factory. I think your best bet is to recalibrate the clock spring using Blue's method, and then determine whether the engine is running lean or rich. FAIW, though, a vacuum of 18 - 19 is fairly decent, assuming your vacuum gauge isn't lying to you. Higher is better, obviously. My engine pulls about 18.5. You shouldn't think of vacuum leaks as contributing to low vacuum, per se. Remember that your throttle body is a huge vacuum leak. Vacuum is an indicator of the running efficiency of your engine. Introduce a larger vacuum leak by opening the throttle a bit, and the engine vacuum will immediately drop and then stabilize at roughly the same vacuum as the RPMs pick up. This all assumes that fuel metering is correct and that you're adding fuel too. If your fuel delivery were too rich, for some reason, and you were to open up a vacuum leak by pulling one of your vacuum hoses, and if the leak were to correct the otherwise rich mixture, your vacuum should stabilize in the neighborhood of 19, even with the leak. See how that works? Anyway, my advice would be to verify the proper condition of every component of the engine (e.g. no vacuum leaks, properly functioning components, proper adjustment of valves, timing, throttle position sensor, AFM clock spring) and then see what your engine does. If necessary, we can adjust the mixture after that.

Also just a theory: Perhaps the PO violated the calibration of the AFM, dialing it in richer (8 teeth?) to compensate for some other problem like a vacuum leak. (It wouldn't be the first time.) Then the problem was corrected, and the AFM remained dialed in rich. Have you tried Blue's patented beer-can method for calibrating the clock spring?

Wow, I apologize for getting in on this thread so late. I saw you already had the best folks in the forum helping you, and I was really busy making a new (to me) house ready for move-in. (We still haven't moved in, but we're getting closer.) Your ECU could indeed have drifted. However, most linear circuits tend to drift in the same direction from copy to copy. I could be wrong, but the drift problem seems to be towards leaner, not richer. Ztrain, on the other hand, has described how his ECU had a solder joint fracture on one of its PC boards (I believe where the main connector was soldered in). A solder joint failure could happen almost anywhere in the ECU, with any number of consequences. I wonder whether that might be your problem. I know it's not a very refined diagnostic method, but what happens if you kick/bump/knock your ECU while your engine is running? Does that affect the running in any way? It might also be worth trying a different ECU. You can sometimes find them pretty cheap. I bought a spare for my '78 off of Ebay for $20. If you have a fractured solder joint, you can of course re-flow it with a soldering iron. Of course you could re-flow all the joints, one by one, in the (likely) event you can't actually find a cold joint visually. Just allow the solder from one joint to re-solidify before moving to the next joint, lest you'll have a resistor drop off the board or something. Be careful to locate wire attachments. When you re-flow one of those, hold the wire to keep it from dropping out of the hole. It's a tedious process, but it might fix the problem.

Blue, yes, your crazy beer-can clockspring calibration method has helped quite a few of us. I've used it, as have Cozye, argneist, Zed Head, and probably countless others. Zed Head and I even played around with a refinement of the method using (US) pennies, which admittedly vary in weight by year. Racebird, hook up your best AFM, leaving the cover plate off, start the engine, and carefully finger the AFM's mechanism a bit more open to provide more fuel. Idle should pick way up, and the engine should smooth out. That's an easy preview of what the potentiometer will do for you.