Zed Head

The N42 block came in the 1978 cars,but the factory head was an N47, same as the N42 but with exhaust liners. The pistons should be dished, but those in your pictures and video are definitely flat-tops. So you don't have a stock 1978 setup. If the head has not been modified you'll have around 9.8 compression ratio. Depending on where your timing was set and some other considerations, you might be close to the detonation threshold. Maybe that timing chain noise was engine knocking? Who knows, different people get different results. Some people have no problems with higher CR, some people have to back off the timing. Flat-tops and an N42 head is not an uncommon combination. Anyway, your engine is not stock for 1978. Somebody has been in there messing around before you got it. Good luck with it.

Leaving the exhaust manifold hooked up - that's another way to do it... It might be just the camera angle but those look like flat top pistons and the exhaust manifold looks like it has the later ZX style diamond shape. Do the exhaust ports in the head have liners? Does the head say P79 or P90 on the passenger side, above the 1 and 2 spark plug holes? Does the block have F54 molded in to it down by the driver's side motor mount? You might have a ZX motor in your 1978 Z. Might be important for parts.

Sounds a lot like the fuel pump cutoff switch, which your 75 should have. With a big vacuum leak, less air goes by the AFM vane, it shuts, opens the contact switch, and kills power to the fuel pump. On Starting the switch is bypassed, so you get another 3 seconds worth of fuel pressure. If you need to keep the engine running so that you can find the vacuum leak, open up the idle screw to get more air past the vane. It will have a high idle though. Or take the cover off of the AFM and tweak the thick wire that opens the switch to keep the switch closed. Have you checked the hoses to the AFM, the breather hose from the top of the valve cover, the oil filler cap and the dip stick tube? All possible leak sources. When I first got my car I did the recommended FSM test of pinching the AFM hose with the engine cold and running and split the hose lengthwise, because it was so old. Couldn't see it but I could hear it.

Is it off yet? My suggestion for removing the head with manifolds attached was short on details. Don't forget to build a wedge for the timing chain, unless you'll be taking the front cover off again.

That's a great writeup, but if you have a hoist to lift the assembly it's also possible to remove the head with the intake and exhaust manifolds attached, along with the fuel lines and injectors. Disconnect the AFM and the injection wiring harness and various vacuum lines, and the exhaust pipe at the flange, then remove all of the head bolts, including the two that bolt to the front cover. Lift the head and manifolds as a unit. It will also allow you to use the manifold as a handle to break the head and gasket loose from the block if they need a little help. Just another option to consider. It's a lot easier to get to the intake and exhaust manifold nuts with everything out of the car. If you don't have a hoist and you're planning to just lift the head off by hand, then weight reduction becomes a consideration.

I don't think that you'll be able to adjust that away. The rocker on lobe #9 sounded really loose also, which is cylinder 5 and also had low pressure in your test. Looks like bent valves. I vote for removing the head. Just one vote, but let's see what the prevailing view turns out to be. Hope that there's no serious piston or bore damage.

Don't forget that idle air/fuel ratio is meant to be controlled by the idle air screw on the AFM. Before you get too carried away with the spring (again). Idle performance is its own little world. There are really just three fuel control areas to worry about - idle, part throttle and open throttle, and only two are really tunable, idle (air screw) and partial (AFM spring). Open throttle is "full enrichment" and will be fuel pressure and injector flow-rate dependent, so can't really be tuned in. There are many other causes for a rich mixture and/or dirty plugs. TPS adjustment, water temp circuit resistance, leaking CSV, leaking injectors, worn rings (oil fouling) are possibilities.

Just registered for me what you meant by arcing from center to negative post. Brain not working right earlier. Still bad, but beerman and SteveJ have the solutions.

Hey, I mis-wrote above. The coil sparks when the ground to the negative post is broken, not made. So the spark jumping to the negative post shouldn't happen unless you have a short in that wire or it's jumping to ground farther down the line. Maybe you have a pinched wire in the distributor.

Not good. Your E12-80 module won't like those voltage spikes since it's on the end of the negative post circuit. You're blasting a lot more voltage through there than it was designed for. How close is the coil negative post to the distributor cap and/or its center wire? That might be the source of the problem. Sounds like it's too close. The spark you're seeing happens when the module grounds the coil negative. So it makes sense that the coil negative post would be a good path to ground. Easier to go there than jumping two gaps. Could also be that your center wire isn't seated completely. That would be three gaps.

How do you know the leak is at the interface between the throttle body and manifold? Have you checked the BCDD? It has a gasketed mounting surface also.

Where exactly is the contact? Is it tire on springs or wheel on tower? I don't see how you could hit the tower without the tire hitting the spring first. Maybe your initial test fit was without tires, or tires with a different profile. As far as the spacers go, I think that if you have sufficient stud length extending through to get good clamping force they should be okay. You might have to install longer studs to be safe. Your wheelbase might be wider or narrower depending on the offset of the wheels subtracted from the offset induced by the spacers. Back to zkars #8 post - maybe the hubs are different in form/appearance, but not function. Same offset and bearing race dimensions, but no effect on usage. By the way, your photo bucket account requires a password to view.

Just realized that a bent valve could also have lots of lash clearance if it's stuck open. olzed's right, spend some time on the easy stuff first. Also, you could always disable three cylinders and just run on the remaining three for a while. olzed has some tips on how to do it.

That's a good point, a head swap might work also. Assuming/hoping, no head bolts break, and that there's no piston or cylinder wall damage. But overall, an engine swap might still be the quickest, most effective way to get on the road. Just because the engines are relatively cheap and easy to remove and re-install. Lots of options, for lots of skill levels. First thing to do is remove the valve cover, and examine the moving parts. You can check lash without loosening any adjustment nuts. A bent valve will probably have zero clearance. Actually, the first thing to do is to download the FSM and read the Engine Tuneup and the Engine Mechanical sections. The first will describe lash measuring and the second will describe what's involved in removing the head. Post some pictures, everyone likes to see damaged parts that aren't their own.

The valve lash adjustment procedure is described in detail in the FSM, Engine Tuneup section. It's a standard maintenance item. But, since you probably did not adjust the lash before you changed the timing chain, I would say that you have some bent valves, based on the 0 and the 58. You will probably notice something different about the way the tops of the valves look on cylinder 2, and maybe 3, when you take the valve cover off. If you don't know how to adjust valve lash, it seems that you got way ahead of yourself when you decided to change the timing chain. If you want to drive the car any time soon, you might be better off to pick up a used L28 and swap it in while you figure out what to do with your damaged engine.

I would determine what the true temperature is before replacing parts. Measure heat if you're concerned about too much of it. Or, if it's the leaks that concern you, focus on fixing leaks. The overflow tube and the thermostat housing are two separate issues. But it sounds like what you're really assuming is that you have a head gasket leaking pressure in to the cooling system. There are products available that will tell if you have combustion products in the coolant. I don't know the names but I've seen them referenced. That might be the first thing to do to determine if you have a head gasket problem, along with checking the oil for coolant (typically shown by brown milky goo on the filler cap or dipstick).

How is your understanding clearer? I mis-wrote earlier. I actually am using a relay from a 1978 parts car that I used to have in my 76, and have a 79 relay for a spare. The part numbers may be different but the functions are the same. Since you're deep in to the wiring diagrams and have the relay out, have you tried just jumping the relevant pins in the connector? That would clearly tell you if the problem is in some kind of short in the relay or if the problem is elsewhere. You're focused on getting an exact replacement part, but you haven't confirmed the source of the problem. Relays are very simple devices.

I was just showing some old discussions for the sake of historical perspective. I think that Blue may be right, this guy might be a genius. He was doing some fantastic stuff back before the Google and the WORLD WIDE web were available. We have it easy. The L-Jet system is primitive, by definition, and there are many different ways to get it to do what you want it to do. I have no idea if the ECU components have aged, causing a drift to lean mixtures, or if the lower energy content of 10% ethanol blends behaves like a lean mixture, or if the lean behavior is inherent to the tune the engineers gave it in the late 70s (the test reports from the car mags reported a lean surge behavior, brand new, using late 70s quality gas). It does seem that the water temp resistance is the popular modification, considering the number of resistors that pop up here and there when current (no pun intended, but still recognized) owners crack open their wiring. It's all good! The more I learn the more I appreciate what the Megasquirt guys are doing. Tuning via computer using wide-band O2 measurement would be so much easier.

On the subject of AFM tuning: I found this web page a little while ago while looking for injector information. It's from the days of Usenet, the very earliest days of world-wide web growth. Somebody collected a bunch of interesting posts and put them in a modern day web page format. This page offers one modification method for someone with a lot of free time. Go to the Index link at the top of the page and browse and you'll see that people were asking the same questions about Z cars 20 years ago. http://yarchive.net/car/z_airflow_sensors.html

It shouldn't matter. I am using my 76 4 speed lever on my 1980 5 speed. The 71B transmission cases, which yours and my (mine?) 4 speeds came with, and which was used in both 4 and 5 speeds up to 1983, all have the shifter attachment in the same location.

It's available at Courtesy Parts. www.courtesyparts.com

The ZX body and suspension is quite a bit different from the Z. Bushing comments about a Z probably aren't especially relevant to the ZX. It's a totally different car.

I've read the 5th gear shift fork is weak on the 5 speeds since it was designed in as an add-on to the 4 speed. You might have a broken fork keeping 5th from engaging completely. It's shared with reverse so reverse might be affected also. That would actually be a pretty easy fix, since 5th gear is in the tail shaft housing. If you have the time to keep the car down, maybe pull the transmission and take the housing off to see. I attached a picture from the 1978 FSM. The ball bearings shown are in the adapter plate which is between the main gear case and the tail shaft housing. You can see that the 5th (OD) and reverse shift fork is essentially half of a full fork.

I've seen someone, maybe FastWoman or SBlake, suggest 5 - 51/2 turns out from all the way in as the factory starting point. I set my 78 AFM there and it was fine. I tried running it in a little to work on that flat spot I described but it just made the exhaust smell gassy so I ran it back out. I usually tune mine by exhaust smell vs. idle quality, unless I have to get emissions tested, then I run it out until I pass the test. Don't forget that the engine is on the idle enrichment circuit when the TPS is at idle. Kind of throws a wrench in the tuning the spring by the fingering the vane method.

I must have looked at the wiring diagram to figure out the operation. I know that I looked at the diagrams to figure out that the 1979 relay would work. I have a 1979 relay in my car now, a 1976 280Z. The part number difference is only for a totally separate blade/pin on the body, for extra grounding, everything else is identical. Yours grounds through the mounting screws. SteveJ may be right on the wiring diagram but I do know that had both solenoids clicking on the bench before I installed it, using a spare 12V battery. You can figure out which wires are the solenoid activators because they will have about 60 ohms (if I recall correctly) resistance through the windings. Good luck with it.