'76 280Z Question on dist/manifold vacuum, dist timing, fuel pressure, brake booster

[FastWoman]

Jenny, you won't need much wire. Just try soldering a joint. I'm sure you'll say, "Oh, gee, wow, that's easy! I don't know what I was ever fretting about."

If I were you, I wouldn't try changing the resistances in the AFM. The CTS circuit resistance will compensate for any out-of-range resistances in the AFM, as long as you get smooth, graded responses from the potentiometer. I get that you don't want to hook up power to the thing, but there's another way. Get an old-style meter (with a needle), and simply measure the resistance between terminals 6 and 7. Don't worry about what the resistances are. Just move the flap smoothly back and forth throughout its range, and make certain the multimeter needle moves smoothly and doesn't jump and skip. That's all. Nothing fancy. If it passes that test, just make certain the spring tension is stock, and put it back on.

Regarding your spherical notch: I have one too. It's just a depression made throughout the years by the pressure of the set screw.

Anyway, get everything back together, find a potentiometer like I linked to (above), solder up some wires that will get you a safe distance away from the fan belts, plug the thing into the CTS connector, and see what CTS resistance your engine "wants" when it's warmed up.

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PS I just upgraded my machine! No, not a laptop. Laptops aren't very useful for photoediting.

Edited February 23, 2011 by FastWoman

[Jennys280Z]

Jenny, you won't need much wire. Just try soldering a joint. I'm sure you'll say, "Oh, gee, wow, that's easy! I don't know what I was ever fretting about."

If I were you, I wouldn't try changing the resistances in the AFM. The CTS circuit resistance will compensate for any out-of-range resistances in the AFM, as long as you get smooth, graded responses from the potentiometer. I get that you don't want to hook up power to the thing, but there's another way. Get an old-style meter (with a needle), and simply measure the resistance between terminals 6 and 7. Don't worry about what the resistances are. Just move the flap smoothly back and forth throughout its range, and make certain the multimeter needle moves smoothly and doesn't jump and skip. That's all. Nothing fancy. If it passes that test, just make certain the spring tension is stock, and put it back on.

Regarding your spherical notch: I have one too. It's just a depression made throughout the years by the pressure of the set screw.

Anyway, get everything back together, find a potentiometer like I linked to (above), solder up some wires that will get you a safe distance away from the fan belts, plug the thing into the CTS connector, and see what CTS resistance your engine "wants" when it's warmed up.

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PS I just upgraded my machine! No, not a laptop. Laptops aren't very useful for photoediting.

I'm going to retire this PC over to one of my parents...I should probably give it another dose of RAM first.

Regarding your spherical notch: I have one too. It's just a depression made throughout the years by the pressure of the set screw.

The locking screw? I doubt that. The screw is spherical underneath?

Remember, I tested the spring resistance of both AFMs per Atlantic. Both were a tad too loose at the midpoint and prescribed water volume, that is, I was slightly past the midpoint with each unit where I should have been right at the middle. It is so slight though that this could be attributed to user error. To have the most consistent results, it'd be nice to have the same tester with multiple units using the exact same criteria, even taking photos for comparison. It's easy to be accurate with small units of measure like pennies or mL of water, however it's on faith how we're reading the angle of the wheel with our eyeballs. No matter how careful and precise we are, there WILL be experimental error, or let's call it variance, across our individual data sets. There's a million reasons why, including what kind of chairs were sitting in when we do the tests. But to be short, it's not just the differences in the numbers in the data, it's the differences across the data sets.

Yes the needle would be far better than the digital but I carefully observed smooth (and identical across AFMS) ohmage increases motion of the flap. Here is a case where you are trusting my eyeballs, but even if you don't, I'm still confident with what I saw and tested myself. Incidentally, the readout from 6-9 on the Python was 352 like I expected it would be (126+226).

Yes I can add a resistor to the water temp sensor circuit....it seems easiest just to pull off the bullet connector, gently solder a resistor onto that and test accordingly. When I get good results on the road, tape it up and be done with it....but I'm not at the point of concluding I need any resistors anywhere at all. My car needs to enjoy a new CTS first...the one I have on the car now is pretty gross looking.

Edited February 23, 2011 by Jennys280Z

[FastWoman]

Jenny, the screw tightens down on a tiny plate that has a dimple in it to grip the clock spring wheel. I think it's that dimple that makes the semispherical dent, at least when it's been tightened down in the same place for decades.

My AFM was also a bit loose per the Atlantic specs, so I tightened it a bit. It's possible the Atlantic spring tension specs are off. They are based on measurements on two used AFMs that were believed to be unmolested. Both AFMs agreed with each other, but it's still a small sample.

You have two good choices for the resistor. One is to put a fixed resistor in the wiring harness where you suggested. The other is to put your variable resistor inside the cabin of the car. However, I wouldn't put a variable resistor under the hood, unless it's designed to be exposed to those harsh conditions. It's very easy to put the variable resistor in series with the #13 wire to your ECU connector. You'll have to unwrap a bit of the harness and then wrap it back up (with electrical tape). It's no big deal. If you do it that way, you can readjust the thing later as needed.

[Jennys280Z]

Update: A new coolant temp sensor and I feel like I'm 99% again. Every part of a major tune up was done to my car save a valve adjustment that I just had 16,000 miles ago. I'll do that in another 10,000-14,000 miles and it looks imminent my Z will now be a part-time driver.

I was on the road today at about 45 mph in 4th gear and I let off the gas to slow down for the light ahead and I "felt" something with the motor "work itself out" and after that it felt like a brand new car.

The drive was amazing today. Smooth, smooth smooth! How much HP does this engine have? 148 HP? I've got to be getting every last one of those! Though my Z is lightened up about 200 pounds. I'm probably 200 pounds lighter than some of the boys on this site (I'm tiny) so on balance my car is weighted about like a 240Z with a heavy driver.

Incidentally, my AFM was adjusted back to the 'sphere' at the 12'oclock position on the wheel at the same time the new sensor went on. Based on how well my car is running, I see no reason not to use this AFM with the 126 and 226 ohm metrics. Confirming what you've been saying all along FastWoman, that the ohm shift doesn't even matter!

You too Cozy wherever you are. btw the work you do on your Z is mindblowing. OMG

And you too Zed Head your advice has been so good at times I felt like doing backflips.

My intuition tells me I might be running a pinch too rich still. Every now and then I smelled gas, and when I was going down a steep hill, off the throttle and in 3rd, I could hear a few gentle pops out the tailpipe. But as far as pickup it's running so right I'm just going to leave it like this. Thank you all! xxx

You guys have made this the best website on the planet for old Z cars. When I can afford it in the near future I'm going to help it for helping me. But the three of you deserve personal accolades. FastWoman, Cozye, and Zed Head.

[FastWoman]

Coolness!

It might have been something electrical that "worked itself out" when coming into the light. I think day-to-day driving is what keeps these old machines going. Little bumps and vibrations keep the electrical contacts moving, and that wears through any corrosion that might accumulate.

It's fine to be SLIGHTLY rich. You just dont' want to be slightly lean. Put in some clean plugs, and read them after a couple hundred miles, just to confirm your mix.

I'm guessing your gentle pops out the tailpipe occur when you take your foot off the accelerator and the RPM drops just below 2500. That's when the ECU starts feeding gas again.

Anyway, this is great news! Another EFI Z is humming along strongly now!

[Jennys280Z]

Coolness!

It might have been something electrical that "worked itself out" when coming into the light. I think day-to-day driving is what keeps these old machines going. Little bumps and vibrations keep the electrical contacts moving, and that wears through any corrosion that might accumulate.

It's fine to be SLIGHTLY rich. You just dont' want to be slightly lean. Put in some clean plugs, and read them after a couple hundred miles, just to confirm your mix.

I'm guessing your gentle pops out the tailpipe occur when you take your foot off the accelerator and the RPM drops just below 2500. That's when the ECU starts feeding gas again.

Anyway, this is great news! Another EFI Z is humming along strongly now!

Good point! I think my RPM was right around 2000-2500 when it did that.

Thanks hon! So do you think that another AFM set to specs would do any good at all? I now have to question if it's possible for my car to run better than it is. I didn't do any WOT driving...just stretching the car's legs for the first time in a while. I suppose I'll have to do that a few times and save that for my final judgment on whether it's strong or not. xx

I cleaned the engine up with Simple Green, and I started the motor wet after rinsing it off and I noticed the idle was low. I tapped the gas pedal a little bit with my fingers and my car went right up to 1300RPM for the first time in forever, indicating a functioning Auxiliary Air Valve. What I'm wondering now is, do these AAVs get "activated" by the throttle somehow? Or they "stick" to that a little throttle wakes them up perhaps?

[FastWoman]

I think the AFM you have is doing just fine. You might have a problem with your BCDD (which leans the mix on deceleration, correcting afterfire), but very few Zs have functional BCDD units. Many are simply removed, and plates are used to cover the hole in the throttle assembly. I don't think mine works at all, but it's still on there.

The AAV is a simple device, activated in no way by the throttle.. I think yours is just sticking. I'm guessing that it will get better with usage. These cars don't like sitting.

I finally had a chance to get my Z out for a fairly long drive, and it came back with a big smile, purring with contentment. Thoughts of that idiot driver that almost hit us tonight were fading away. Before long, the weather will be a bit warmer, and I'll be doing a few other little jobs on it, as well as on its younger siblings, the little red Miata and the work-horse Saturn.

[cozye]

Good news! sounds like you've made some progress. Sorry,, I'm still around. I've just been very, very busy with work and the very few moments I've had here and there I've spent working on my projects. My pc time has been limited to just a minute here and there.

[Jennys280Z]

Got a new computer put together over the weekend and forgot my password to log on here!

FastWoman: Some maniac almost hit you, oh no!! :mad:

You've got a stable full of rides on your hands now to play with. You'll get all Mazda'd and then not be here as often!

cozye:

It's good to see you're back. I'm still reading your posts on other threads so your wisdom succeeds you!

But I'm salivating over this now:

http://cgi.ebay.com/ebaymotors/DATSUN-280Z-TOTAL-Polyurethane-Bushing-Kit-14-2002-B-_W0QQcmdZViewItemQQhashZitem53d3c533c5QQitemZ360035201989QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

Do you think I could handle putting this stuff on my car? At least part of it?

All:

The good: Okay so after a few more road tests...I was puttering out the tailpipe a little more frequently, so I backed the timing off from 12 back to 10 and that stopped completely. Running smooth on the road...no smoke, no smell, no backfire.

The bad: I drew a little graph of what I think is still happening with my car. It maps mixture to engine speed. The curve shape is conjectural. Maybe I drew the shape backwards. But I think I have the bug of it right.

A little history: I started out focusing too much on the idle, realized that enriching the idle could get me from 14 to 17inHg but the car ran pig rich on the road like that. If a lean mixture is causing my idle problems, and a rich mixture while driving is causing dead cylinders via fouled plugs (a repetitive event in my car's history), then maybe the way in which my AFM is defective is altering the mixture curve.

Referring to the graph, the dark dotted curve is where I should be. The curve with the solid line is where I am now. The error in mixture at lower RPMs (idle) is more severe, whereas the error at higher RPMs is barely noticeable. But I'm questioning if it's possible to pull the ends out in both directions, "stretching" out the curve to exhibit two symptoms simultaneously and making my car a biach to diagnose. What do you guys think? Plausible?

I just realized yesterday that I still haven't tried the idle adjuster on the AFM yet. I'll do that tomorrow. I fingertipped the chuck of metal on my AFM again yesterday and the idle increased dramatically with a few millimeters of adjustment open. Idle decreased very quickly with a mm or two closed. Manifold vacuum still below 15inHg at warm idle. But on the road the car runs well again. For the first time since I've participated in these boards, I got three consistent test drive results! And the car responding very well to changes like retarding the timing.

[cozye]

The bushing install is a big job, for sure. I'm sure you could do it if you put your mind to it, but it will be a major PITA. It will involve a lot of work, a lot of PB plaster, a lot of burning out old bushings with a torch and cutting sleeves out with a hack saw. Also, I wouldn't bother with the bushings without doing the springs and strut cartridges as well, but thats just me. Unless you are just looking for a big project to learn from, I'd consider just paying someone to do it honestly. It took me about a week and a half to do it, working several hours a night.

[FastWoman]

Jenny, I've never gotten that deep into polyurethane bushings but know people who have. Their advice to others is almost universally that it's easy to go overbaord and have your ride responding with the harshness of a buck ford. If I were you, I think I'd just replace what needs replacement as it needs it, and if the fresh rubber bushings don't do the job for you, then consider poly -- unless you're trying to put together a track car that you don't intend to drive on the streets.

Your mixture: If nudging the AFM vane with your finger caused that much of a change in idle, I'd say you're idling way too lean -- the same way I was. You can try cranking in the idle mix screw (clockwise) to richen the idle mix without richening the higher-throttle mix. My screw didn't do much for me, though. Maybe yours will. I bet when you crank the thing in, your idle will hardly budge. Mine didn't. It's interesting that later versions of the AFM had two idle mix adjustment screws instead of the one. I don't know why that would be, except that it suggests they weren't happy with the way the original AFM adjusted.

Again, my fix was the resistor. I think I'm now a bit on the rich side, judging from the light deposit of exhaust soot around the exhaust tip. I suspect my plugs will read a bit rich too. So I might back off the resistor a bit. The nice thing is that I have that option now on my car.

[Jennys280Z]

Jenny, the screw tightens down on a tiny plate that has a dimple in it to grip the clock spring wheel. I think it's that dimple that makes the semispherical dent, at least when it's been tightened down in the same place for decades.

Well the car feels so good it must be close to as good as it can be. After I drive it for awhile it keeps running better and better. After long drives (10 miles or more) it always comes into the garage idling at a very steady 900-950 RPM but just warming up isn't good enough to do that. It has to be driven. Maybe this will change soon as I drive it more frequently...but anyway the drive tonight was so much fun. I can barely feel my foot on the gas and the car just moves out in every gear. Feels like a sports car again!

Oh I still have the cold idle issue, only now it's at 700 RPM and not 550 RPM. Dunno why. Maybe my air regulator cleaning made that much of a difference.

I tried to manipulate that idle mixture screw and just like yours, it didn't do anything. I had the digital tach hooked up, was listening closely. I cranked on it CW for a while and just about all that happened was I smelled gasoline after a point. And I hate how there's no frames of reference on this thing!

Oh and as for the AFM wheel, I think you're right. I got a flashlight and a magnifying glass and looked at the meter I bought very carefully and I could see some of the other teeth "dug" into a little bit too. I loosened the locking nut and I was wrong. The glue had been broken. But there is one very prominent semisphere carved into the wheel and like you said that is likely where the locking nut was for most of the AFM's life. Which means that wow, my AFM was adjusted way farther towards lean than I thought it was. (And still is). That tooth is at 11:55 right now, where on the locking nut it's what? 10:00 or 10:30?