Captain Obvious

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.

And by the way, the other thing you do with the Steinhart-Hart coefficients is use them to build your look-up table. There aren't nearly enough data points in the FSM and if you try to linearly interpolate between only what's published, your error will be huge at the midpoint between your table points. Back in the Mesozoic Era when I used to do this... First thing you need to do is determine the amount of acceptable error. Then you calculate enough data points along the curve such that the linear interpolation between your table points never varies more than your max error budget from ideal. Works out such that the table points will be farther apart in areas where the curve is naturally more linear, but in the areas where the curve is nasty, you'll need more points. Did I say that right?

Haha! Honestly, I'm not sure which I'd rather tune... Off the top of my head though, I'm going with the triples.

Lenny, are you kidding me??? All that floating point and you're gonna use a look-up table for the conversion? You don't have to be embarrassed... I'm embarrassed for you. I'm just kidding of course. But if it were me, I wouldn't even ever convert the resistance to a temperature. The ECU doesn't really even ever need to know the "real" temperature in degree units. The only reason you need that is so you can display it on your interface. All the ECU really needs to know is how much fuel to add to base at that resistance (voltage actually) sensor input. Lookup table... Volts in, and increment to base pulse width out. Who cares what that is in "degrees". And BTW, there was some problem with the numbers in the FSM. I did a post about it a while ago. Let me see if I can dig that up. On edit - Found it: http://www.classiczcars.com/forums/fuel-injection-s30/48782-water-temp-sensor-air-temp-sensor-resistance-charts-typos-manuals.html

My read is that everything is working as best it can and you're simply at the mercy of mid-seventies control technology. Once the engine is fully warm, it will idle smooth at 800-900 with no AAR help, but it sounds like the AAR is closing off before the engine has warmed up to the point where it will sustain that idle. Unless you turn up a hard issue with one of the FI components, your (only?) choice would be to adjust the AAR so that it's open more and takes longer to close. Of course, that will mean that your initial cold idle will be higher, and you might not like that, but that's what I meant about being at the mercy of the old tech. The AAR's closing speed is based on things that are out of the control of the ECU, and there's no ECU control of the idle speed. It's the best they had back then.

And the potential confusion about the proper install direction of the rubber bushings continues... If you look closely at these pics, you'll notice that they couldn't make up their mind and installed one bushing each way. One had the thick rubber section towards the frame hole and the other has the thick rubber section towards the large washer: [ATTACH=CONFIG]66175[/ATTACH][ATTACH=CONFIG]66177[/ATTACH]

Lenny, A while ago I derived the Steinhart-Hart coefficients for the air and water temperature sensors. Don't know if you're beyond this point already or you were even planning to use this method to determine temperatures, but here's what I got: C = 1.89571E-07 B = 0.000257545 A = 0.001305386 These numbers are based on info from the FSM and I believe they are slightly suspect. If you find from experiment that they are off a little, let me know and I've got a different set of cooefs that were derived from info directly from Bosch instead of from Datsun.

Chas, That setup was put together from two kits and I did it that way based on info gleaned from other's previous experience about breaking T/C rods. My PO had put poly at all four bushing locations (so I already had the poly). I replaced the rear poly bushings with rubber ones from that AC Delco kit in the pic. I bought two of those kits because I needed washers and sleeves for both sides, but only used half the bushings. I highly recommend that AC Delco kit by the way. Quality was excellent. I just wish I had taken a new pic after I spun those rubber bushings around. I hate posting that old pic knowing that it risks others making that same mistake simply out of example. It's on the car now and I didn't take a pic after I fixed them...