Captain Obvious

I'm talking about the 280Z intake. Something that uses the same bolt pattern as 75-78. What I would really like to find is something that bolts on and has provisions for an idle air valve of some sort. I'm musing getting rid of my AAR and instead replacing it with something built right into the throttle body. Nice video Blue. Looks almost like a pupil. Wonder what the performance advantage is. Less obstruction when fully open? More linear flow vs position?

What alternative throttle body options are available? Weber (and it's clone). 240SX Q45 Anything else? Anything that bolts up and has the same internal throat bore? What about from other manufactures? Doesn't have to be Nissan...

When it comes to needles and nozzles, tiny changes can have surprisingly large impacts. Just one thousandth can have a noticeable effect.

Kurbycar, Thanks for the input. I didn't get the chance to do any experimentation yet. Soon I hope. See here's one of the problems. I would love to use a higher power higher quality aftermarket head unit, but I've looked at a bunch of aftermarket stuff and I don't think what I want exists... (anymore). Everything aftermarket is loaded with too much crap with tiny buttons on multi-colored distracting dynamic displays. Put the stuff I use the most on the left and the stuff I use the least on the right. Don't put all sorts of crap around the volume knob that I'll hit by accident in the dark. Keep it simple.

Cool. Glad you found the problem. That's why I specifically sald "and lay it against the engine." I don't want no willy nilly hunt. I want it to go directly back to engine ground just like the spark plugs do. You're right... Disabling the low side of the coil is actually a safer way to disable the spark. The reason I suggested the coil wire instead of the low voltage side is that you can do it in an instant without tools. It's faster, easier, and just as safe and effective, if you do it right. I should have been more specific and said "After you pull the coil wire out of the distributor, you'll notice that there is a metal end on it where it connects into the distributor cap. Lay the coil wire against the engine in such a way that the metal end makes electrical contact to a good ground connection to something like the intake manifold or valve cover." Better?

The reason people have suggested an ignition timing issue or plug wires on the wrong plugs is because if you get a spark too early as the piston is coming up, the explosion inside the cylinder will push back down on the piston and fight the starter. If this happens, the explosion will stop the starter spinning very abruptly like you described. Pull the coil wire out of the center of the distributor cap and lay it against the engine. Then crank the engine over while that coil wire is removed and if the problem goes away, then you know it's some sort of ignition timing problem. And I don't think your starter is the problem, but the above wouldn't tell you much anyway. Under a no load condition, I don't think you'd learn much from measuring the voltage drop across the starter. It's more of a current thing than a voltage thing.

And Blue... Mi casa es su casa! I'll show you my newest secret projects in the lab. :tapemouth

Thanks again guys. I'm going to retry my pre-packaged speakers in the Z and make sure I was hearing what I thought I was hearing. I've also got two or three aftermarket head units sitting on the shelf that I could throw in temporarily just to try to see if they sound any better. I'm sure the aftermarkets I have include better output stages than the Kia. Wouldn't solve the problem, but might help me identify if the problem is at the source or the destination. Ironically I've been on the inside of more car stereos than I can count... I was the repair tech at an audio video store for a couple years to get through college. I can make them work, but apparently can't make them sound good!

Shouldn't always be your first inclination, but there are times when it's appropriate, right? You do know that driving around with that can of freeze spray in the glove box will probably be your insurance that it won't happen again, don't you? :laugh:

Mike, Thanks for the thoughts. I did not install sealing around the edges of the board in which the speakers are installed, but it's a pretty tight fit even without seals. I understand the theory, but I believe that level of improvement is in the minutia. I'm no expert on the topic (obviously), but I think I'm looking for big steps first. Short story on the speaker polarity is that I know it's correct. Longer story is that months ago when I did this install, I even went so far as to doubt the accuracy of the markings stamped onto the back of the speakers. So I took turns with each speaker hooked up to a DC source and verified the direction of the cone travel. I can guarantee that I've got the speaker polarities correct and they are all pushing in phase. I've got a pair of pre-boxed speakers (ones with their own enclosure) installed in a different car. In that other car, they sound pretty good. Memory says I tried those boxed speakers in the Z and they didn't sound as good in the Z as they did in the other car, but maybe I should try that again...

I know it's kinda shotgun approach, but I'd pick up a can of that spray cooler stuff and take it with you next time you get to the car. If the problem recurs, I'd pop the distributor cap and give everything inside a quick shot of the cooler and then snap the cap back on and see what happens.

That should make it easier to find, right? Mixture screws don't do that. Stop-n-go driving isn't a particularly high fuel consumption situation. You've got way more fuel flowing through the carb (per unit time) on the highway than you do during stop-n-go. And the temperature things is weird for fuel supply. I'm having a hard time coming up with any sort of fuel supply issue that's temperature related. And certainly nothing that "latches" into a problem state as you've described. Besides, it's not mid-summer anymore. If it's got a temperature related issue at this time of year, what was it like this past summer? I'm thinking electrical... What's in the distributor? Is that the Pertronix?

Thanks much for the help guys! djwarner, The head unit came from a Kia Spectra. Didn't make note of the year, but they used this radio (and like two others that are pretty much identical to it) in almost all the later model single-DIN Hyundai's and Kia's before they started going double-DIN. There are like three single-DIN models that all have the same faceplate functions, but the buttons are moved around to different locations. It's my assumption that the majority (if not all) of the electronics behind the faceplates are pretty much identical. I do not know for sure if there was a subwoofer used in the original installations, but I doubt it. I can tell you however that there are no subwoofer specific connections on the back of the head unit. I can also tell you that if they did use a sub in the original application, it used high level inputs because there are no low level outputs from the head unit. Walter, That's also a very good question, and I do not know the answer. I bought this model because it had the mechanical and human interface features I wanted, but I have no idea how it sounded. For all I know, it sounds just as good (bad) in my car as it did in the OEM installation. Kinda stupid, I know... So if it's just a crappy radio, can I throw additional equipment at it to make it better, or am I back at square one looking for a different head unit?

I'm having a hard time forming a mental picture of what the symptoms are... You're saying that it runs fine when you first start it and it continues to run fine until you do some stop-n-go type of driving? And then after the stop-n-go, you can get onto the highway and the problem goes away all by itself after a couple highway miles?

The speakers are 6x9 Sony Xplods that came with the car from the PO: They are mounted right behind the seats into the 280's false pressboard hatch area floor so there's plenty of volume on the back side of the speakers.. Location is such that the magnets hang right over the cargo hatch recesses. The only amp I have is the one located in the head unit, and to be honest, I suspect that's my problem. My suspicion is that the factory head unit just doesn't have the balls to drive the low frequencies to the speakers and that's why I get no bottom end. However, before I simply start throwing money and equipment at the problem, I was hoping there was some way to confirm what's going on. I know "doesn't sound good" is very subjective, but are there tests I can run? Questions that can be answered? Better descriptions of what I hear that can be provided? You know... The kind of stuff that the audio-geeks live for!

I recently put a newish radio in my Z. I've got a long list of "What I was looking for in a radio", and the best thing I found for the features I was looking for was out of a Kia (also used in Hyundai): The mechanical install turned out great, and I really like the way it looks and feels. Problem is... It doesn't sound good. The system works as intended, but I want more bass, especially at low volume. It's like the bass is barely there at mid-volumes, and completely disappears at low volume. I don't know if the problem is the head unit, the speakers or something else. Have we got any audiophiles in the braintrust that can bring me up to speed with theory stuff?

Haha. Memory? Naaa... I looked at the wiring diagram. I didn't spend a lot of time on it, but I'm going with that read unless someone convinces me otherwise.

Still a typo. 75-77 used the AFM switch. 78 used alternator output AND oil pressure switch. Then in 79, the ECU took over.

I believe they switched from the finned aluminum cover to the black painted steel case on the 260 to 280 changeover. The 260 used the finned aluminum and the 280 used the black painted modules. So, you were thinking that your original module was getting way to hot... Does the new replacement get hot too, or has swapping the module taken care of that issue? I popped the cover off the 280 style a while back. Exactly what you would expect... Lots of mid-seventies discrete electronics. With the easily obtainable alternatives (like ZX or GM HEI) I wasn't interested enough to do any reverse engineering. Interested enough just to peek around, but didn't trace anything.

That's why I took that pic with the box and P/N visible. I've found it a great help to do stuff like that. It just removes all ambiguity about what the number was and what was included with the kit. I bought mine from Rock Auto, and yes, they are listed incorrectly. I should have mentioned that... Actually, I was keeping that as my own little secret so the next time I needed more, they wouldn't be all bought up by other Z owners. :laugh:

High-tech back in 1450 as originally invented by Leon Battista Alberti! There isn't any technical info in those articles, just history and a pic or two. The pic I linked to above is Robert Hooke's anemometer from the mid-1600's. And yes, it's the same Hooke as "Hookes Law" (the spring guy). About the cross sectional area, it does change as the vane lifts up. I have absolutely no idea how linear the pot output is however. One of the sources I found indicated that it was intentionally non-linear and was in fact a logarithmic output. If it were me, I would put it in series with a known transfer function mass flow meter and pump some air through it at varying rates and characterize it. I wouldn't try to predict the output... I would cheat and test it.

Actually it traces directly back to what is called a "Pressure Plate Anemometer". See: pdf doc about instrumentation Anemometers More about instrumentation

I'm no expert on the topic, but I believe the flowmeter style used in the L-jet is more akin to an anemometer in that it measures more "flow velocity" than "flow volume". Of course, if you know the cross sectional area and the velocity, you can calculate volumetric flow per unit time. I'm assuming this is the same thing you found out with your research and why you said "For a compressible fluid, it's all about the speed." Is that the case?

Be warned that the AAR adjustment is finicky... A lot of adjustment made through a very small amount of movement of the adjuster nut. And it's spring loaded inside to boot. I suggest you mark it well with a fine point marker for your initial position before you loosen anything so you know where you started and can always go back to that spot in the future if necessary. Good luck, we're all counting on you.

Zed Head, To be honest, I'm not totally convinced on the "correct" direction of those bushings either. On my 280, I originally installed them as shown in the pic above, but then after a few days I spun the rears around because of what I found on a "probably" unmolested 260. This 260 wasn't purchased new, but had been in the family early enough that I doubt the front end needed that kind of work before purchase, and I'm sure that it wasn't messed with once in the family. So unless it needed bushings very early on and was done before entering our stable, it came from the factory with the thin part of the rubber bushings towards the frame. It was strong enough data for me that I spun my rear rubber bushings around. But I could still be convinced either way with even stronger data. I've got pics of the 260 bushings around here somewhere and if I can put my hands on them, I'll post something.