FastWoman

Are you doing this because of your hot restart issue? It sounds like a lot of work for something you might not like as much. I'd suggest simply removing the ECU and AFM, but leaving the wiring for a while, until you know carburetors are what you really want to run. Seriously, ball up all the wiring, wrap it up in electrical tape, and zip-tie it out of harm's way for a year or two. Then after your first carb rebuild (because of ethanol gas), contemplate whether you might want to go back to EFI. If you do, the wiring is there waiting for you. Depending on the carbs you're running, you might have an electric choke. Run that to IGN +12, and you'll be set. That's all the engine wiring. The ignition will stay the same. Save all your EFI parts. Put them in a box. Even if you don't want them again, others might. Oh, use Stabil fuel stabilizer, and don't let your gasoline get old. The ethanol will really be cruel to your carbs if you don't take these precautions.

Matt, what sort of filter are you using? The OEM design of filter is quite large, and I've not seen a clear one of that size. There are some clear, low-flow filters for carburetors. When running one of those on a carbureted 318, there were times the filter appeared to be empty, when in fact it just had an air pocket. It was still passing fuel just fine. That said, an OEM fuel filter is oriented in such a way that any air inside the filter should be purged. You would see nothing but fuel in the filter, if you could see through the metal can. I'm guessing your issue is simply one of the fuel pump fading. As your pump is new, I'm guessing your electrical connections aren't in good shape. You should trace all your connectors from the fuel pump relay to the pump. Check that the connections are clean and solid (and haven't charred/arced). After cleaning, grease each connection with dielectric grease to preserve it. First stop is the fuel pump relay connector, inside the big, black box on the passenger side of the engine compartment. The blue/green wire leads to the pump. Second stop is the big wiring tree connector (there are two of them) just inside the passenger firewall. This is where I had a melted, charred connector. I snipped out the blue/green wire and connected via a bullet connector. Last stop is the fuel pump. Also check your ground, which runs from the pump, through a bushing in the floor, and to the interior of the cabin. FAIW, 35-36 psi running pressure and 40 psi non-running pressure is a bit high. Non-running pressure (during cranking, or also with vacuum line disconnected) should be 36. Idling should be about 29 if your engine is running efficiently -- higher if it's not. The 4-5 psi differential you're getting between non-running and running should be more like 7 psi. This tells me your engine is either running rich or lean. If your fuel pressure gauge is accurate, your high pressure might have your engine running rich. That would indicate a fuel pressure regulator issue. It's more likely your gauge is off, though.

When you push the AFM open, what you're doing is delivering more fuel (and the same amount of air). In other words, you're richening the mixture by pushing the AFM flap open. Considering you've already replaced or tried swapping everything, I think you probably have some vacuum leak issues (probably big ones). You should start by replacing every inch of vacuum line. Then check for vacuum leaks with the "yogurt cup test." After you've eliminated rotten tubing, the following common leak sources are left: -- Intake manifold - to -head junction, especially around #1 and #6 -- Bad power brake booster -- Ripped/cracked "accordion" boot between AFM and throttle, resulting in unmetered air -- Disconnected or improperly connected vacuum lines -- Leaking items connected to vacuum lines, e.g. mode selector switch for heat/AC system (which can be re-furbed very easily) Have you checked your throttle position sensor? It's the little square, black switch assembly on the side of your throttle. It should be adjusted per the FSM. You might also have an ECU drift issue. The Hitachi ECUs ('78 and I believe also '77) tend to drift leaner and leaner with age. This can be corrected by adding the right resistance to the coolant temp sensor circuit. If you do want or need a new ECU, Superlen has been working on one specific to the Z and will be releasing it pretty soon. The intent is that it will be plug-and-play, or as close to P&P as is feasible with these old cars. It's called "Hellfire," and there are a couple of current threads about it.

Hi JR, Thanks for the update! The EFI Z is a very reliable ride, IMO, once you pound out the decades of neglect from previous owners. There are articles here... somewhere... about refurbing the directional switch. There's even someone who will do it for you. Post a question in the electrical forum. My advice: In addition to refurbing the directional switch, replace both flasher units (direction and hazard) with electronic ones. It's cheap, and it reduces current draw on these fragile and precious switches. Also consider LED replacement bulbs.

Not practical enough for school? Geesh, it was a GREAT car for school when I went to college and graduate school. The daily commute was as awesome as a commute could be, and there was no end to the stuff you could fit in the hatch. Go figure... Anyway, CL is probably the best place to advertise. I've never had trouble selling cars there. What's helped me has been sparkly clean vehicles (including engine detailing), combined with very good photography (I'm a photographer). One thing that could be hurting you is the automatic transmission. It's rare and interesting, but it's not desirable.

An inline 6 is going to be no more or less responsive than any other geometry of engine, in terms of response lag, power, or whatever. Power is more a matter of displacement, head design, and other factors that are somewhat over my head. Response lag mostly has to do with the intake. What an inline 6 (and not a V6) gives you is perfect primary and secondary balance, unlike any other engine configuration except a V12. It's smooth and light -- my favorite type of engine. Even better, the L24/26/28 has a lovely chain-driven OHC, an honest flat tappet valve train on which you can adjust the lash (a strangely satisfying job), and 7 main crank bearings. It's a really tough engine. But is a 2.8L I6 going to be as powerful as a 350ci (5.7L) V8? Well.... probably not. But it's going to be a sweet engine nevertheless, delivering an honest 150 hp, give or take, in its stock configuration. Will you humiliate anyone in a late model Camaro? Probably not. But you don't have to. You'll look and feel twice as cool. As for the responsiveness of the stock engines: I can't speak for the carbureted engines, because I've never driven a carbureted Z. But the EFI 280Z is VERY responsive when it's in proper repair. Punch the pedal, and it goes.

Rossiz, if your EFI setup is running great right now, I'd just do what's necessary to keep it running that way. That means cleaning or replacing every EFI connector under the hood. (They're all available on ebay.) As long as you do that, your EFI will keep running about the same. As for the hot restart problem, the new check valve will probably take care of most of the problem. I can't help you with the teenage daughter problem. I once had a gorgeous '66 Mustang, and my kids (both boys) were mortified to be seen in it. It was "old" -- not like one of those nice SUVs that respectable people drove. Go figure. Much later, my stepson, then a 20-something young man, began to appreciate my 'Stang, but alas it was time to sell it and move on to a Z, which is what I really should have been driving all along. But with a young/teenage kid, if the car doesn't immediately and effortlessly "turn on" when you turn the key, then it's deemed an embarrassing piece of junk. Anyway, assuming you resolve most of the hot restart issue, if you have such an incident, raise the hood to let the engine cool. Try the key again in 2-5 min, and you'll be on your way. Wiggle a few things confidently and authoritatively while you're waiting, and you'll look like a hero. You can also wire a switch to your fuel pump relay with three positions: First position (momentary), you feed +12 to the relay to run the pump and prime the fuel rail. Second position, the pump is connected normally. Third position interrupts the 12V to the relay, so that the pump won't run. In the third position (momentary), you can crank your engine without fuel to clear any flooded cylinders. Oh, and FAIW, the hot restart problem won't happen until the car has been sitting for at least 10 min. So if you stall your engine for some reason, you can restart it. You'll find the only time you have a hot restart problem is when the car is parked, so you won't be in a bad position.

If you HAVE TO go to carburetion, which you probably can guess I feel is a big mistake, for God's sake, stay away from the Holley 4-barrel! I slapped a Holley on our boat, and it worked great for a season. Then the ethanol gas got the better of it. So I replaced it with another Holley, which was good for a season. Then I rebuilt the first one, and it ran like @#$%. Then I rebuilt the second, and a fuel plug started leaking. I brazed over it and patched it back together, but the little accelerator pump rubber doodad ripped. Expensive little piece of rubber! The carb still didn't work right. So I paid a lot of money to have it professionally rebuilt. It ran OK, but not great. Then we sold the boat, and that fixed the problem. The Holley is the WORST carb I've ever rebuilt, and being a child of the 60's, I've rebuilt many. FAIW, the SU looks like a really nice design. I think I'd try a nice pair of those. Better still, give the EFI half a chance.

The thing is, olzed, the air would be cooler in front of the radiator than behind it. Having once lived in a pretty dusty area, I would have guessed air from the engine compartment might carry a bit less dust than air from the front-side of the radiator, particularly if it had to circle back. These snorkels extend down close to the road in some more recent models of cars. There have been cases in which engines would suck up massive amounts of water when driving through puddles. The water would then hydrolock the engine. Because the engine would be spinning at a good clip, naturally something would bust -- a piston rod, the crank shaft, or whatever. At least ours draw in air from up high.

HR369, those are interesting looking accumulators -- different from what I was understanding! They appear to have a vacuum fitting on the back end. Mentally reverse-engineering the things, if I'm understanding right, the pressure of the accumulator would rapidly track changes in the manifold vacuum, essentially maintaining constant pressure across the injector. In that case (with the vacuum fitting), that WOULD work. Furthermore, this accumulator design would raise the fuel rail pressure to 36 psi immediately upon engine shut-down, rather than the typical running pressure of 29 psi. This would help prevent vaporization. Are these mounted on the fuel pump assembly, with vacuum lines running that entire distance from the intake manifold, or are they mounted in a cooler part of the engine compartment, where a shorter run of vacuum line would be required? I'm wondering whether a part like this could be mounted in the vicinity of the fuel filter. If we're right about hot injectors flashing fuel that flows into them, this accumulator idea would not be a panacea, but it might help. It's interesting the Jeep folks have the same problem. Do the Jeeps have these accumulators? There shouldn't be any issue with weakness in the check valve. These valves fail through wear. If you've replaced yours and are still having your pressure leak down, you probably have an issue elsewhere -- FPR, injector, cold start injector. FAIW, I'm running the same Volvo check valve, along with new injectors, and my system holds pressure almost indefinitely. So there's no design issue with the check valve not being strong enough. Others have suggested the more massive exhaust manifold, relative to headers, would hold and radiate more heat, and I suspect there's merit to that thought. I suspect beefier manifolds would only aggravate the problem. Perhaps someone will will pipe in and say, "I had hot restart issues until I replaced my manifold with headers." FAIW, there was an evolution of manifold design over the years. In '75/'76, the intake manifold had no webbing and would allow free airflow from the exhaust manifold, up around the intake runners. In '77/'78, there was webbing between the intake runners and heat shielding around the exhaust manifold -- both between the exhaust and intake, and surrounding the exhaust. Then of course they went with the fan in '79.

Well, when the pressure NEEDS to drop, this is achieved by the FPR spilling fuel into the return line. If there's no accumulator, relatively little fuel needs to be spilled to drop the pressure. On the other hand, if you have an accumulator full of pressurized fuel, much of the volume of that accumulator must be spilled before the pressure can drop. More spillage into the return line takes more time, hence less responsiveness. And then when pressure must again be built, that's accomplished by the FPR blocking fuel flow to the return line. However, the pump no longer simply has to repressurize the line. Instead, it has to fill up an accumulator, which again takes time and decreases responsiveness. Not mentioned in all of this, an accumulator could increase the work load of the pump considerably, as the pump would have to keep re-filling it after every dumping. As I said, I can see an accumulator being useful in a constant pressure system, but the L-Jet system is NOT constant pressure.

Are you sure that's all water? It sounds like phase separation, and the stuff on the bottom would appear to be the ethanol/water mixture. Your engine can (barely) run on it. See here: Phase Separation in Ethanol Blended Gasoline This still points to a water condensation problem, whether it's yours or the station's. I'd start buying my fuel elsewhere. You might also use a fuel stabilizer like Stabil. There might be another explanation as well, unlikely though it might be. I'm reminded of a friend whose little boy told her, "I filled your gas tank, Mommy!" And indeed he had -- with sand. This is of course related to another incident, with another friend, in which her son said, "I sanded your car for you, Mommy!" And he had done exactly that. Anyway, you should make certain you don't have a little helper who pours water into your tank.

Site, the '75 I owned in my youth didn't have the snorkel, and it ran fine. My '78 has the snorkel. I'm certain it must have some sort of purpose, but it escapes me what it might be.

HR369, if you were to install a pressure gauge anywhere in the system from the outlet of the fuel pump, to the injectors, to the inlet of the FPR, you would find that the pressure jumps up and down right along with intake manifold pressure. The FPR bottles up a 36 psi pressure differential between the fuel rail and the interior of the intake manifold, but because engine vacuum jumps up and down, so must fuel pressure. Any attempt to stabilize fuel pressure (with respect to atmospheric pressure) is going to make the system less responsive. BTW, I mucked up my description of the fuel pressure compensation in my prior post. Throttle open -> vacuum drops -> fuel pressure increases (relative to atmospheric pressure). Throttle closed -> vacuum intensifies -> fuel pressure decreases (relative to atmospheric pressure).

HR369, yes, I've noticed that after shutoff, the fuel pressure will slowly rise from its normal operating pressure to a plateau at the FPR's bleed-off pressure. One can only presume fuel is bleeding off into the return line at that point. This could be confirmed, of course, by removing the return line and watching what comes out (and when). It's worth noting that I've observed this on a warm (but not blistering hot) day in the shade with the hood standing open. This is one reason I believe the problem is heat passing directly from the cylinder head to the injectors. The accumulator sounds interesting, but I would think it might create a performance changes. When the throttle is suddenly opened up, the intake manifold pressure rises (vacuum decreases), and then the fuel pressure must be dropped by the FPR to compensate. There would be a lag created by the accumulator, as more fuel would have to be bled off for the pressure to drop. And then as the throttle is closed, fuel pressure would have to increase accordingly. It would take time to fill the accumulator back up. I wonder if the accumulator is used in a constant pressure scenario (not regulated in relation to intake vacuum).

First thing: DON'T run an engine on ancient gas! You might spray varnish all over your valve stems, which can solidify when the engine cools. And then when the valves are stuck in place, you can bend them the next time your start the engine. I did this once, and trust me that you don't want to repeat my mistake. That said... Nice looking car! Great color! Congratulations, and welcome!

Failing ignition? The fact that you can ease into a higher RPM might be simply that you have a weak enough spark that it fails to jump the gap when the engine is under load.

Very nice, Captain!

I wouldn't worry about the blip. I don't think it means anything -- likely a bit of current through a relay contact before the relay energizes. Pressure readings: Your gauge could easily be inaccurate. It should read 36 psi when cranking, but if voltage is low, it might not. When the engine is running, there's a vacuum in the intake manifold. The pressure difference across the injector -- from the fuel rail to the interior of the intake manifold, is regulated at 36 psi. When you rev the engine, air rushes into the intake manifold, and the vacuum lessens. As a result, the fuel pressure WITH RESPECT TO ATMOSPHERIC PRESSURE rises by the same amount. The result is that the pressure difference across the injector remains constant. So yes, fuel pressure should fluctuate to track the intake vacuum. That's normal and good. Pressure leak-down can be due to leaky injectors, but it's more likely due to a leaky check valve on the outlet of the fuel pump. This part is no longer available, but I believe someone on our list found a substitute for it. You can also order an aftermarket check valve that you can install just before the fuel rail. See here: One Way Check Valve for Gas or Diesel Fuel 5 16" Bio | eBay Your check valve should hold the pressure at least until your engine has cooled down. If you lose all your pressure in 30 min, that could be the cause of (or a contributing factor to) your hot restart problem. I'd say your system is leak-free enough if you maintain at least 20 psi for maybe a couple of hours. In the event your injectors do leak fuel into the intake manifold, I suppose some of the gasoline could get into your oil. However, we're talking about so little gasoline. I really don't think it would cause a problem.

Rossiz, I permanently installed a hardware-store-variety pressure gauge between my fuel filter and fuel rail. It's a made-in-china water pressure gauge for a well pump system. The gauge is 1/8" MPT and is screwed into a brass "T" fitting with three 1/8" FPT inlets. I have two barbs threaded into the other two legs. It's worked great. I think I paid about $10-15 in parts.

It sounds like you are looking at the correct solution. Your oil pump was probably installed on the wrong tooth. I worked on that part of my '75 decades ago, but if memory serves, it was a somewhat miserable job. I think it would have been much easier if I had a volunteer top-side to tell me when the shaft was oriented correctly.

To be clear, Swede, the stock configuration is with a cast iron exhaust manifold, not headers. If you have headers and hot-restart issues, then that would put a dent in the heat-soak theory. Where are you in the US? And is your hot restart problem a summertime problem, or is it year-round?

hr369, several of us have ruled out leak-down issues. My Z will hold fuel pressure just about forever, and it still has occasional hot start issues. I think our operating conclusion is that it's a design problem, hence Nissan's approaches of introducing hood vents in 1977 and an injector cooling fan with the ZX in 1979, and possibly even replacing the aluminum insulators with plastic. It might also have to do with ethanol gas, or winter gas formulations used in summer, which might vaporize at lower pressures.

Thanks for starting this, Zed! Mine is a 1978, stock EFI with new Standard FJ3 injectors with plastic insulators, stock exhaust manifold, all 1978 heat shields intact, and fuel rail covered in rubber hose. The engine is tight and runs very well with a CTS resistance mod. I USUALLY don't get hot restart issues. But SOMETIMES it does happen. Engine starts easily, but seems to be running on 2-3 cylinders. All cylinders fire up the first time I put the engine under load and stomp on the gas. Just revving the engine will work, but I have to do it for a while. FAIW, my hot restart problem was worse before I rebuilt my intake system. When I changed out my injectors, I retired the aluminum insulators and installed plastic. Perhaps that helped?

I see you're a mere 20 years old and lack the perspective that comes with age! And I would trade places with you in a heartbeat! (Great car, BTW -- all the better to own at age 20! ) Unless you hang out with old car enthusiasts, you wouldn't know how bad the tail end of an old car really smells. But I do. I remember being stuck in traffic in the passenger seat of an AMC Gremlin on the San Diego Freeway in the early 1970's -- without A/C. By the time we reached our destination, our eyes were bloodshot, and we could hardly breathe anymore. California eventually led the nation in emissions control, and now the urban air in California is almost breathable. Modern car exhaust smells as fresh as springtime in the Rockies (well, not really), thanks to very precise fuel injection systems and catalytic converters. Now, your 240Z, with old SU carbs and no catalytic converter, will always smell somewhat gassy if it's tuned right. If you were to tune (most of) the gassy smell out of it, it would sometimes be running lean, and that's not good for the engine. That's just how it is. If you would like cleaner smelling exhaust, you might consider installing a good quality of catalytic converter. You can do that for a carbureted engine, so long as you don't tune it too rich. If you want to entertain a project, you can also fuel inject the engine. The EFI of an L28 should bolt right up to your L24 engine. Superlen is currently developing an ECU for our engines that will make them run even better, with O2 sensor feedback, modern digital circuitry, and lots of great goodies. We're all very excited about it. This, with a catalytic converter on the tailpipe, should have your exhaust smelling like that of a modern car. You'll also enjoy greater responsiveness and much better fuel economy.