Zed Head

Realized that I was looking at the wrong wire in the 76 diagram. There are three connected to negative, the big cable to the starter lug, a wire to ground, and another (the one we're talking about) which connects to 5, 16, 17 and 35 and the coolant temperature sensor. A dedicated isolated ground for the EFI system, apparently. 5 is also connected to 72 of the EFI relay. In short, the star ground shown in the Engine Fuel chapter, with 5, 16, 17, 35, 49 and 72 is actually the dedicated wire to the negative post. If that wire is disconnected, parts or maybe all of the EFI system is not grounded. New learning for me. superlen must know this but I was never sure of what that wire was connected to. I sure didn't know that it was the ground for the coolant temperature sensor. It should be a focal point for anyone seeing high resistance on the coolant temp. circuit. I went out and measured resistance from that small gauge ground wire back to the battery negative post and got 63 ohms. Resistance from the negative post to the valve cover was 0.7 ohms (control measurement). I assume that I was measuring resistance back through some resistors or transistors to ground. So, connecting those wires backward at the battery may or may not be guaranteed to cause damage. It's not a direct short but it's not open either. Had to write all that down just to burn it in to my brain.

I feel compelled to emphasize for any future readers of this thread, do not switch the positive and negative small gauge wires at the battery in an attempt to fix a "no injector pulse" or "no fuel pump power" problem. Bad things might happen. This thread is a special case of lucky. There must either be a mistake in the wring diagram or the car in this case has a ground wire that is not actually grounded. I have a 76 and will check that ground wire when I get a chance to see what's what, but the solution here is not quite right. It bugs me.

Any details on the GUI? Are you a programmer also? I Googled "Hellfire" and now I'm probably on somebody's watch list....

The BCDD is an emissions device, but not the most effective. It's main purpose is to let a little extra air past the throttle blades to burn fuel on deceleration while in gear. According to the FSM (Emissions chapter) it should only be replaced as a unit. They might still be available for only $252! Datsun 280Z E.F.I.(2) -Air Flow- L28E ASSY-BCDD :: Nissan Parts, NISMO and Nissan Accessories - Courtesyparts.com

The timing mark that you see is only relative to piston #1's position when the spark occurs in the wire to cylinder #1. Doesn't really matter how the spark happened, the oil pump could be off 80 degrees. That is assuming that the mark on the damper pulley is in the right place. Have you checked piston and camshaft position when the mark is at zero? The piston should be at the very top of its stroke (top dead center/TDC) and the camshaft should have both valves closed. Dampers do go bad and the mark can move. You might have a bad damper and a misplaced timing mark. Your pulley is kind of odd looking, with the teeth on the pulley. But I have a 280Z so maybe that's normal for the 240's.

Glad you found a solution although I have to say it doesn't make sense to me. The small gauge wire from the positive post is the EFI power supply. I can see how not having that connected would allow everything to work except the EFI components. But connecting the EFI power directly to the small gauge ground spade should have caused a short. I think. Maybe that is the EFI ground only and its isolated from the others. Or maybe yours is not connected to anything and you got lucky. The diagram shows it as connected to body earth so there should have been big sparks as soon as the small gauge positive was connected to it, shorting back through the large negative cable. Anyway, good luck and carry on.

Who knows what the other three shops did but it seems like the ground connection at the battery would be okay since the electrical system is right enough to give spark. And he has a good starter now. Looks like he's down to the fairly typical problems of no injector activity and problems making the fuel pump run. The ECU grounds the injectors base on the discharging of the coil with voltage pulses transmitted through the wire from the negative post of the coil to Pin 1 of the ECU through the blue wire. The tachometer and its in-line resistor need to be in place for the ECU to do that correctly (in case you have some things torn apart). Of course, the other half of that relay is the EFI relay. Have you measured voltage at the injector connectors with the key on? You should have 12 volts on both sides. Which I see that you have in Post 11. Check the circuit from the coil negative to Pin 1 at the ECU. You should have continuity.

Yes, they both are limited at the high end. The Chilton and Haynes books are notorious for having sketchy, mainly generic, advice. The FSM is the way to go. But, in looking at the 1972 FSM I can see where your problem lies, they don't say much, and the idle settings are pretty low, even for a good running engine. Looks difficult. I'll step out of the carb conversations. Looks like a messy scene. Edit - just looked at the 1973 procedure and it makes even less sense to me. If you do things in order, timing is set with load on the engine for an automatic, shift lever at "D", and the vacuum advance actuator hose connected, then the hose is disconnected for further tune-up operations. So, my comments above about what to do with the vacuum hose were totally wrong for the 240Z's and don't match anything I've ever seen on the US market cars I've worked on. Weird stuff. Good luck

Saw this today. Fun to just view the pictures, especially if you like the color blue. Notice the new vents behind the painted over 240Z symbol and the ZX fuel system cooling fan, cooling the carbs. No offense intended if it's a forum member. The car just has some unusual features. Rare Gem 1973 Nissian 240z ROAD READY

In other words, the zero at 550 RPM is actually zero at 1100 engine RPM. That's why the FSM maintenance procedures and the sticker under the hood always call out an RPM at which to set timing. Another thing that is typical of factory settings is that the vacuum advance actuator is connected to "ported" vacuum. Ported vacuum is not active when the throttle is closed, so there is no need to disconnect the hose. So the procedure does not call for disconnecting the hose. Some people though, in their modification efforts, connect the vacuum advance directly to intake vacuum. The early carb'ed engines may also run full time vacuum from the factory though, I'm not familiar with their details. In that case you would want to disconnect the hose, since engine speed and intake vacuum will cause variation. You kind of have to get in to the details of your own set-up, and whether it's factory stock or has been played with.

You're welcome. I'm glad that one of my goofy garage tricks worked for someone else. I have more.

I think that the question of the distributor being off one tooth has been ignored because the engine ran before. It's kind of irrelevant, and a red herring, which will distract you from what's really wrong. The oil pump drive can be off one tooth, which then puts the distributor off because the distributor is driven by the oil pump. If you never too the oil pump out and the engine ran before, then the oil pump should not be the source of your problem. Transistor ignition systems can fail partially, to where they'll give spark, but not a strong spark. You may be getting spark outside the cylinder but not inside under pressure and fuel/air mixture. The suggestions about re-installing the points are good ones. Go back to what you know worked, take out the unknowns. In other words, try to get the engine back to exactly like it was when it ran, then start the improvement cycle over again.

Do you have vacuum advance connected? If someone connected the hose to full-time vacuum, you might have been reading timing incorrectly. The vacuum advance canister should not have vacuum when setting static timing. People mess with this quite often, although many people with carbs don't even use it at all.

I see a few possible clues. Things initially went bad when you took the carbs apart. Then you did a bunch of things, possibly fixing the original problem, but also maybe creating a new one or two. One possibility is that you installed the new wires in reverse rotational order. The engine will run this way, I've done it, on fewer cylinders. The fact that you have spark on all wires but the engine won't run seems to fit. Also, once the engine starts but has some dead cylinders, the other plugs can foul. I would pull all of the plugs, clean them up and reset all of the wires. 153624, counterclockwise. Make sure the rotor is pointing at the #1 terminal of the cap when the timing mark is in the vicinity of #1's timing setting.

I think you might be better off if you just spent a little time studying the system. It's actually super simple. Just think of two pistons that are connected by the hydraulic tube, that move the same amount. Then adjust the metal pieces on each end (the slave cylinder rod and the clutch pedal linkage) so that there is very little play in either. Make sure the slave cylinder piston is starting from just off the bottom of its stroke (described by EuroDat above). Make sure the clevis pin and the hole in the clutch pedal aren't worn out (they do wear out, causing lots of slop). That's pretty much it, no FSM needed.

Rockauto shows .030" over as available. RockAuto Parts Catalog In general, I've heard that if you go outside recommended that you should have the remaining cylinder wall thickness measured. Some blocks can take it, some can't. But 0.120" seems way over recommended, I don't think that's possible.

There are only two basic things you need to work with on the clutch hydraulic system - starting point and travel. The travel is determined by how the master cylinder's movement is transferred to the slave cylinder. The starting point is determine by the mechanical components. I don't know the spec. on travel but the posts above suggest it's about 35 mm or 1 3/8". If you're only seeing 1/2" of travel, it's either because the rod from the pedal to the master cylinder is moving without pushing the master cylinder piston, or the master cylinder piston is moving without pushing fluid. The slave cylinder is self-adjusting due to the internal spring, so it's not really an issue unless it's leaking. I left some detail out but that would be my basic starting point. To reiterate - if the slave cylinder is not leaking, it's not your problem. It only responds to the fluid being pushed in to it. If your not getting full travel, it's because the mechanical linkage is not adjusted correctly or the master cylinder is leaking internally. Blue must have been having a bad day. He seems yo be ignoring the fact that the specs. that the Asian companies use are set by the their "Western" company contractual counterparts. In other words, if your "Made in China" part has problems it's because your American company is making profit at your expense. There are many many high quality products made in Asia. Nest time you're looking at your fantastic picture quality big screen TV, amazed at today's' modern technology, look at where it was made. Probably China.

You should be posting in the Classifieds section. There's a link at the top of the page.

You might consider that taking the engine apart is for your learning experience but buying a used, good condition engine (they are out there) to put back in is the economical choice. If the head gasket is new that means the IPO has been in there, which is not a good thing. You've had a poor lubricant running through the engine so there's probably extra wear on various bearing surfaces. You have a variety of broken parts. It's not you vs. the engine anymore, it's you vs. the PO's errors.

So is the popping and backfiring still there or does it run poorly in a different way? What's the current state of engine operation? You might have problems masking problems, or a problem that comes and goes which is what your first post suggested. If the engine runs well sometimes then you should probably hold off on big things like manifold gaskets. It's unlikely that they would vary between bad and good.

On #2, the stalling, I would say that your AFM fuel pump contact needs a little adjustment, or that you have a vacuum leak. If the contacts are off a little bit, a low idle will cut power to the fuel pump when air flow through the AFM lets the vane close too much. Bit in your case you say that you have power to the pump when the key is turned on, which is not the way the factory built them. If you have fuel, you should be able to drop your idle speed down below 1000 RPM easily. The jumpy tach and the cut out could be tied to the ignition system. What is this "upgrade"? There are many varieties.

There might be a misunderstanding here on the details. The contact switch in the AFM closes (makes contact) when the AFM vane (flap) is opened. This allows power to the relay which then powers the pump, assuming that the initial power sources are correct. If you take the black cover off of the side of the AFM you can see the mechanism. I've had the AFM contacts get contaminated (on a "new" MSA AFM) to where they look like they're touching but they're not really making electrical contact. I had to give them a buffing with a match box strike pad to get them back in order. You can check that the contacts are closing by testing for continuity at the AFM with it removed or at the EFI relay plug (it takes some study to figure out which wires go to the AFM contacts). I would check those AFM contacts before going too much further.

It's looking more and more like you either bought your car from someone who thought they knew what they were doing and was way over-confident or you got scammed. Since you've found the source of the water/oil leaks maybe you don't need to remove the head. Can you tell if it's ever been removed before (new gaskets, etc.)? If not, you might be able to get back in to running shape with just the timing chain cover work.

When you came back with AFM testing I assumed that you had fixed the fuel pressure drop problem. I'm guessing now that you did not. The EFI must have proper fuel pressure to work correctly. There's no way around it. 26 psi is probably the lowest pressure number you should ever see on these engines. Don't get distracted by the new pump or the recently cleaned tank. Something is still wrong with your fuel system.

The popping is a typical sign of lean mixture and the fact that it's worse as it gets cold fits. The fuel pump contacts are only for the relay and will not cause problems since yours runs all the time. 60 ohms is about right for a relay, but in your case the relay is not being used so it doesn't really matter. 60 ohms is also about right for the AAR citcuit. That is the resistance of the heater wire inthe AAR. looks good. What you need to measure is Pin 8 to Pin 6 (180 ohms) and Pin 9 to Pin 8 (100 ohms). Measure at the ECU connector if you can. IF you're using the 1980 EFI Handbook, they would be tests #1-3A 1975-78, and test #1 3C 1975-78 Those are the circuits that control the fuel mixture. I have a theory that as long as the ratio of those two is 1.8 the AFM will work correctly, but if you're way off, typically the engine will run lean, causing popping and backfiring.