FastWoman

Tomo, I have to disagree. There's no reason, IMO, that a replacement ECU has to be digital, and there's no reason you can't tune an analog ECU. I see this as being a two-stage process, just off the cuff: The first stage is to create a base pulse from the AFM reading. You'd use an op amp to follow the AFM output voltage and then ramp the voltage of a capacitor by applying that voltage. Then you'd run that to a comparator. I suppose you could have a variable resistance charging the capacitor, giving you a primary adjustment for the base pulse width. The second stage is to generate reference voltages for the other input of the comparator. There would be a base voltage, set by a potentiometer, leading to an op amp follower, which inputs via a fixed resistor into an additive op amp circuit whose output feeds to the comparator. Additional inputs to the additive op amp would be for the CTS (send current through fixed resistor and through CTS, amplify/offset voltage, with 2 adjustments); for the ATS (same treatment as CTS), for the TPS (adjustable fixed voltages applied for idle and WOT enrichment); for the O2 sensor -- probably a low-pass treatment of the O2 sensor signal by charging/discharging a capacitor. (I think it would be a very good idea to upgrade the system with the O2 sensor, but this sensor could be omitted from an installation if desired.) There would be a counter circuit to reset the ramp on the capacitor the AFM signal charges with every 3rd spark. When the ramp is reset, fuel is sprayed until the AFM circuit's voltage exceeds the additive circuit's voltage. Then fuel flow is cut off. The cold start is not controlled by the ECU, so it can stay as currently wired. I was wrong before to say that a multiplier circuit would be required. I think the whole thing could be handled with conventional, ubiquitous op amps. The hardest part is coming up with the time to do it! While it's easy to envision the building blocks of the system, prototyping and debugging the whole thing can be a bear, especially since some of it has to be done "in the field."

Captain, I remember giving the answer similar to the one your cartoon on an organic chem midterm back in the Jurassic era. I got partial credit for the chutzpah. I drew a magician's hat with the reactants, a reaction arrow with magic words underneath and a magic wand overhead, a "poof" and then the same hat full of product. But back to the ECU, I understand that a MS board can already process input from antiquated hardware like air flow meters, so I don't think any additional ADC work is needed -- but I could be wrong. I doubt there would be such a flood of people wanting replacement 280 ECUs that it would be worth reinventing MS's wheel. Instead, perhaps someone could just figure out the easiest turn-key retrofit, possibly programming in the necessary parameters before shipping a MS system wired into a 280 ECU's box. I'm thinking of some sort of program whereby somebody could send in an OEM ECU, working or not, and have it gutted and retrofitted with a pre-programmed MS board for reinstallation. Or maybe it's not that easy.

LOL Oh, WOW! Uh, gee... So you want someone to tackle the black box part?! LOL But seriously, I suspect some custom implementation of a MS system, cobbled into an L28 box, would be the way to go. Perhaps there are even a few unused pins for connecting an O2 sensor. I do admit, though, it would be fun to have an analog replacement ECU, just for grins. Perhaps this appeals to me only because I used to design analog circuits. Op amps are commonplace, and it would be easy to design a socketed board based on a commonplace pinout, as OP amps are fairly substitutable for a low frequency, low voltage application such as this. The magical hurdle to jump would be to introduce multiplication into the mix for compensation of fuel mixture for air temp, engine temp, throttle sensor status. That takes special chips that never seem to stay around very long. Analog Devices used to make a bunch of them, typically with product cycles of a couple of years (?). I don't know if these things are even made anymore, now that digital devices are so commonplace. Even after getting that far, I don't know what happens after the AFM pegs. Is there further enrichment based on RPM?

Chas, Lenny (superlen) seems to have evaporated. I tried PMing him a long time ago, and I still have no response.

{{I have no doubt that the head isn't flat}} Is this a misstatement on your part? You're saying you're certain the head is NOT flat? If this is what you're saying, then you should definitely have the head milled flat -- without question! Having a machine shop do the required work on a head is quite cheap. I wouldn't hesitate to have the head professionally rebuilt, just because. FAIW, I've found a milled coarse file is wonderful for cleaning off mating surfaces. Here's one: FK SKS Milled Coarse File 100mm - Edge And Wax They're a bit hard to find, but they're very flat, and they aggressively remove whatever is on the surface, without removing underlying material, provided you use them carefully. That said, I would still take the head to a machine shop. Have it done right!

Tomo, FAIW, there's not enough information in the TR7 schematic to duplicate its ECU, unless you happen to have a source of supply of the proprietary ICs (big, black rectangles on the schematic with many, many connections each). Those ICs are little black boxes, so to speak. I suspect an EFI system could be retrofitted that uses an air flow meter or MAF sensor and controls a 6 cyl engine (either inline or V), provided the same injector flow rate is used, and provided it has a vacuum-regulated fuel pressure regulator. I think that would remove all the mystery variables, such as the air flow properties of a different intake manifold. Then again, a MegaSquirt system would seem the obvious way to go, if someone would only build/preprogram a drop-in replacement (wired into the same ECU box) that would use the same sensors (including the AFM). That would preserve the vintage Rube Goldberg look and feel of the L-Jet system, while introducing digital reliability.

I bought an '81 new. It was great to drive, but the body was junk. The plastics in the car melted in the Texas sun, the electrical system has Lucas reliability, parts broke for no reason. When I was fed up with the car, I decided to sell it and bought a used '75 280Z -- best car I've ever had. For a few months I owned both. Fast forward almost 2 decades decades, after my ex made me sell my '75 Z, my ex became my ex, and I sorely missed the Z. I bought my '78 to replace the hole left in my life. Then my partner wanted a convertible. The first gen Miata seemed an obvious choice, but I was terrified of having another experience like with the RX-7. Happily, Mazda seems to have improved considerably. The Miata is a great little car. The second engine (1.8L) is even kinda' good on torque. I did like that little Wankel, though.

The sending unit isn't on the top of the tank, beneath a round inspection hole in the hatch floor (round plate approx. 6" dia with 3 screws)?? It is on my '78. I don't know about the '75.

It's my understanding that a larger throttle body won't increase airflow, because the limiting factor of the intake manifold throat diameter still remains. If you get desperate for a replacement air temp sensor, perhaps a coolant temp sensor's tip could be cut off with a tubing cutter, revealing a thermistor within? Then the thermistor could be snipped loose, have wires soldered to it, and encased in epoxy. A mold could be made by pressing the old air temp sensor into modeling clay and then using the mold for pouring the epoxy. It would be a good idea to use a good structural filler to keep the thing from cracking apart with age, as the debris would be gulped into the engine -- probably harmlessly, but who knows?

Ya think?! I don't go to that shop anymore. FAIW, I had a rusted fuel intake repaired somehow long, long ago on the '75 I drove in graduate school. I don't know specifically how it was repaired and can't remember what it cost, but I do remember it wasn't particularly expensive.

Nathan, go to the hardware store, and buy a cheap water pressure gauge ($5-10 in the well pump section), a brass "T" that it will screw into, and two 5/16" nipples that will also screw into it. Then insert the gauge inline between the fuel filter and fuel rail. The gauge won't be dead-on accurate (being a cheap gauge), but it will be good for monitoring what generally goes on with your fuel pressure. You can leave it permanently installed. When you shut down the engine, the fuel pressure should remain high, in the neighborhood of 29 psi (36.3 minus 7.something for idle vacuum). It should ideally stay there forever, until you restart the car. Mine will retain pressure for at least a week (the longest I've gone between runs). A tiny bit of leakdown is normal. I think if you lose half of your pressure over a period of maybe several hours, you have a minor problem, or you can at least improve the situation. There's a check valve on the fuel pump that prevents backflow, and there is the fuel pressure regulator that prevents pressure release to the return line. And then all your injectors must also be tight as well. What you might find with the hot-restart problem (if you have it) is that fuel pressure rises after engine shut-down, as fuel is heated, expands, and (controversially) may become vaporized by the engine heat. (Our engines run at very low fuel pressure and were not designed for modern ethanol gas.) The pressure will rise to 36.3 (?) psi, at which point excess pressure (and fuel) will be spilled to the return line through the fuel pressure regulator. Then the engine will cool, and the gasoline will condense, causing pressure to fall, possibly to a vacuum. At that point air may be drawn into the fuel rail, if there is any leakage in the injectors. Then on startup, your system is injecting air, rather than fuel, and it takes a while for the air to clear. (Or so one theory goes.) Another hot restart theory is that gasoline in the injector pintle is superheated and flashes to vapor when the injector opens, so less fuel is delivered as a vapor than as a liquid. The situation resolves when the injector is cooled by the vaporizing fuel. You won't see this issue reflected as much in the fuel pressure. I'm uncertain from your description whether this is a hot restart issue you're describing or just a restart issue. Is the engine hardest to restart maybe a half hour after shutdown and then easier after it's been sitting overnight? If so, then it's hot restart and may relate to fuel pressure leakdown, combined with heat soaking of the fuel injection rail. If it's an ordinary restart issue, then it may simply be fuel pressure leakdown by itself. Either way, the cure involves resolving all of the sources of leakdown. If it's a hot restart issue, you might have some additional success by changing fuel formulations, installing a 280ZX blower (for cooling, not for forced induction), insulating your fuel rail, and/or changing out the aluminum insulators at the base of each injector to the plastic type. PS the cold start valve is only actuated when the engine temperature is below 50degF.

That's actually how most of the carbureted cars ran. Most fuel injected cars did start and run, without any re-start or throttle-goosing necessary. Both carb and EFI ran great when new/fresh, of course. It's just that it took much more deterioration/wear/tear/time/corrosion/whatever for an EFI engine to get to that point. They were less fussy. Anyway, my comment was meant mostly jokingly. Only speaking for myself, my car starts and runs at the first turn of the key, regardless of temperature, but its EFI is in unusually good shape for an L-Jet system. Many L-Jet 280s have mysterious hot-restart issues, but even these can be resolved with enough fiddling. Fuel rail pressure leak-down is another really common problem and could be responsible for your initial starting issues.

Nathan, that's how MOST cars used to run back in the day! So instead of getting self-conscious, you might pop the hood, jiggle or tap some random part, try starting (successfully) again, shrug, and say, "Heh... antique sports cars!" My guess would be fuel rail leak-down as well.

I was quoted $400 by a radiator shop to split the tank, clean it out, epoxy-coat the inside, and reassemble. That seemed pretty steep to me, so I didn't do it. Repairing/replacing/refabricating the pickup should be a relatively minor addition to that job.

Is your clutch pedal adjusted correctly? The push rod is adjustable from under the dashboard. First enlist the help of a friendly leprechaun to climb up under your dash. Tell him to loosen the jam nut on the push rod, adjust the length to take up the slack, and then re-tighten the jam nut. Wade: "That will be one six pack of beer, please." Here we are at the beginning of a new year. Isn't it about time you admit you have a problem? Hmmmm?

Silly Northerners, salt is for food!

Ah! While I was typing, so were you! Well, I'm glad you found the problem.

The same thing happened to me. I found a connector that had apparently had engine coolant dripped on it (heater core connections overhead), which caused the wires to slowly corrode away. One of the wires pulled completely out. The connector was green (not antifreeze green, but copper corrosion green). I just wired in a new connector, and all was well. BTW, the problem occurred when I did some work in the central console area and had undone some nearby electrical connectors. I suppose that was all that was necessary for that last wire strand to break.

Wade, I would think almost anything is possible with a Volvo!! (Must have been a generator, not an alternator?) However, true alternators aren't going to work that way. They are going to produce the same polarity of output irrespective of the direction of rotation or field winding polarity. In fact the GM alternator on our Chrysler 318 boat was rotated backwards and produced the correct polarity. Polarity is all straightened out in the conversion from AC to DC by the rectifier bridge. The +12 output goes to the "ALT" post, and the ground goes to the case. It would be impossible to miswire it. Again, all bets are off with a brush-type generator, but an alternator should be pretty hard to miswire (er... unless the negative also went to a post, instead of the case? Would Volvo do something dumb like that?). To me it sounds like malibud has a bad battery or some humungous short somewhere for the battery to drain down that fast. And I still wouldn't rule out a bad alternator. I would think even the '75 alternators should kick out 14V well before 2500 RPM. My '78 puts out 14V at idle, even when re-charging the battery right after a start. If I load the system with headlights and emergency flashers, then I get a bit of voltage sag until I come off of idle. While I realize both the alternator and battery tested good, sometimes the employees at the auto parts stores don't know how to test these things correctly. This wouldn't be the first time a bad part was tested as "good." You would think this would be such a costly mistake to them that they wouldn't make it!

Punishing my son?! He currently drives a rusty '90 Volvo brick that barely runs and has a Christmas tree dashboard. This is an upgrade!

Bhermes, just to be clear, a vacuum reading won't tell you whether you have a vacuum leak, popular expectations to the contrary. For instance, you could have a bad coolant temp sensor, causing your engine to run rich. This by itself could cause your vacuum to be low/weak. Then you could open up a big vacuum leak that would compensate for the richness, and that would cause the engine vacuum to strengthen. Engine vacuum is more an indicator of engine running efficiency than anything else. If everything is right with the engine, your vacuum will be somewhere in the 17-20 range, depending on compression/wear. As mentioned above, my proprietary, patented "yogurt cup test" will tell you whether you have any vacuum leaks. It's very easy to perform. I'm not understanding about the sending unit either. It's just an arm with a float in the fuel tank. There's no pickup tube. Surely he's referring to another part.

IMO, there's no reason not to clean the internals. Here's what I'd do: When you're ready to change the oil, go ahead and pop off the valve cover. Give the internals a good scrubbing with Chemtool B-12, Gunk engine flush, or perhaps even kerosene. Use a toothbrush to scrub all the junk down. Blot it up with paper towels, and after all the solvent is gone, vacuum up any loose debris, and blow out the area with compressed air. Don't worry about any of the dirt/debris falling/draining down the timing chain tunnel. Just chase it down with some additional solvent. AFTER YOU DO THIS, DO NOT START YOUR ENGINE! Simply remove the drain plug, and all the junk will be safely swept out with the motor oil. Afterwards, run a diesel formulation motor oil (I use Chevron Delo), and change it when it starts looking pretty black or 3000 mi or 6 mo, whichever comes first. Use a good filter like K&N, Bosch, or Mobil 1. (I like K&N.)

Thanks, Blue!

The olive green plastic-coated and galvanized (underneath the plastic) lines they sell look pretty good and are apparently bendable even by hand (although I would still use a bending tool). Supposedly those lines hold up 30x as well as the OEM. Copper alloy sounds like a really good idea, but I'd have to do my own flares. I'd do it for the Z, because I don't want ANY corrosion (even cosmetic), and because I'd know if I had a leak. However, I don't trust my son to recognize a leak until his brakes would get dodgy. I think it's better to go with the sure-fire factory flares in his case. I suspect the olive green steel brake lines will outlast most young drivers' vehicles anyway. I'm going to do whatever is necessary to make this job easy on my back. I'll have someone else put the car on stands/ramps with my supervision, and then I'll finally buy a creeper, so that I can skate around under the bottom of the car with ease. I'll also have a helper close at hand to pass me tools and parts, so that I don't have to twist my back (which is how I get myself into trouble). If I keep my back flat to the creeper as much as possible, I should be just fine.

Well, in all fairness, my back is getting better. It's not painful, just fragile. I've been pushing the ibuprofen and getting my rest. Update: Now not only do they want me to pay them for the work I specifically told them not to do (splicing the brake line), but they also suggested they could do the job correctly for another 6.5 hours in labor. Yeah, right! I told them I would take the matter up with their corporate office. After that I complain to the state police, the attorney general, the BBB, the various review boards, etc. If they push me far enough, I'll spend quite a bit of time slinging crap their way, just out of principle and to protect other people from these crooks.