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

[FastWoman]

Oh, and perhaps I didn't answer the question you were really asking: The ratio of these resistances is almost spot-on identical -- .5555555 vs. .5575221. That's identical in automotive terms.

As for failure modes -- perhaps the carbon traces absorb moisture and loose their compactness as they expand and contract over the decades. That would drive resistance up. But again, it's no problem if all the carbon traces are drifting towards higher resistance in the same way. The voltage ratios will remain the same. I'm sure the Bosch and Hitachi engineers designed the various components with this dynamic in mind. (I certainly would have done that myself.)

[Zed Head]

In looking at the U/Ub diagram you can say that Ub is definitely affected independently of U, by the off-spec. 126 ohm value, but can't say for sure if U is affected at all.

I was hoping to be able to calculate some real numbers but can't do it with the Pin 8-9 measurement.

Pin 8-9 measures R0 (100 or 126 ohms), so that affects Ub. But pin 8-6 includes the potentiometer and R10. If the potentiometer has higher resistance, then U and Ub might effectively cancel out, for the purpose of the AFM. But if R10 is the higher resistance and the potentiometer is unchanged, then voltage Ub is effectively lower (the sum of the resistances is higher) and the ratio is off. U/Ub would be higher than expected, which would create a lean mixture from the ECU (based on the fact that voltage is higher with the vane close - less fuel needed)). Since it is split and starts at 1:1 (the penny/quarter data) I would estimate the voltage error back to the ECU could be 12.5%. The highest voltages are sent at low rpm so low to part-throttle would be lean.

There could be a logic error in all of the writing above, but in short, you can see that it is possible that the potentiometer resistance that affects U is unchanged. Therefore the U/Ub relationship could be off, with the higher 126 and 226 resistance readings.

I almost bought one from Python Jenny. They didn't have mine in stock though so I went with MSA. Since you have three AFMs now maybe you could measure the voltage ratio of at least one, with closed vane. You should get about 50% of the input voltage across 7 and 8 with power in at 6 and 9. Any low amp battery will work, even a C or D cell. If you get 50%, then I will move on from the resistance readings, until some future date.

My car is a 1/76 build and had the A31-060-001 AFM.

It took me a while to get this all down so looks like I missed a bunch of new posts. No time to read them right now. Good luck.

Edited February 20, 2011 by Zed Head

[FastWoman]

Zed, all the resistive material laid down on the potentiometer board should be the exact same stuff. If it all changes resistive properties the same, then all the resistances would change by the same proportion (including the carbon trace that the wiper glides along). Therefore the voltages relationships should remain the same.

[Jennys280Z]

No worries, Jenny. You have every reason to be frustrated right now. These old cars can get pretty funky, and they stay funky until you find all the problems. I think the best perspective to have is to keep tinkering, be happy when it runs, be thrilled with any improvements along the way, and keep tinkering. Eventually your car will be right again.

You know....

Eric might disagree with me about this, but I suppose an argument could be made that you DON'T have to have everything perfect before making the mixture adjustments that we've been recommending. This frustrating process has been a bit like Master-san training young Grasshopper mechanic, starting with wipe on, wipe off.

Maybe the more sane approach (that will keep your spirits up) is to fix everthing you see that obviously needs fixing, leave unknown stuff for the future, install a variable resistor in your coolant temp sensor circuit to adjust your mixture, and enjoy your car. Then whenever you discover and fix a new problem that might alter your mixture, simply readjust your mixture.

Contemplate this procedure:

1) Get a 5 kOhm variable resistor from Radio Shack. Set it to roughly 2.5 kOhms Attach two wires to it, and plug those wires into the CTS connector (the harness side).

2) Start your engine. Adjust the variable resistor for the smoothest idle.

3) As your engine continues to warm up, keep adjusting the variable resistor to maintain a smooth idle.

4) When the engine is fully warmed up, do a very careful adjustment of the variable resistor to achieve the highest engine vacuum. Then shut your engine down.

5) Measure the resistance of the variable resistor, and measure the resistance of the CTS. Calculate the difference.

6) Report back, and I'll help you figure out what resistance to wire where, in order to achieve a good idle.

7) Wire in your extra resistance, and give your car a test drive. You can adjust the resistance a bit, if necessary, to fine tune it.

8) Love Cars, Love People, Love Life. Enjoy the ride.

Wow that's cool!! I think I could actually handle that! Remember I can do simpler things. x

I'm going to stick with classiczcars and MSA. xoxo

This site isn't just an automotive clinic, it's also a counseling center

[Jennys280Z]

In looking at the U/Ub diagram you can say that Ub is definitely affected independently of U, by the off-spec. 126 ohm value, but can't say for sure if U is affected at all.

I was hoping to be able to calculate some real numbers but can't do it with the Pin 8-9 measurement.

Pin 8-9 measures R0 (100 or 126 ohms), so that affects Ub. But pin 8-6 includes the potentiometer and R10. If the potentiometer has higher resistance, then U and Ub might effectively cancel out, for the purpose of the AFM. But if R10 is the higher resistance and the potentiometer is unchanged, then voltage Ub is effectively lower (the sum of the resistances is higher) and the ratio is off. U/Ub would be higher than expected, which would create a lean mixture from the ECU (based on the fact that voltage is higher with the vane close - less fuel needed)). Since it is split and starts at 1:1 (the penny/quarter data) I would estimate the voltage error back to the ECU could be 12.5%. The highest voltages are sent at low rpm so low to part-throttle would be lean.

There could be a logic error in all of the writing above, but in short, you can see that it is possible that the potentiometer resistance that affects U is unchanged. Therefore the U/Ub relationship could be off, with the higher 126 and 226 resistance readings.

I almost bought one from Python Jenny. They didn't have mine in stock though so I went with MSA. Since you have three AFMs now maybe you could measure the voltage ratio of at least one, with closed vane. You should get about 50% of the input voltage across 7 and 8 with power in at 6 and 9. Any low amp battery will work, even a C or D cell. If you get 50%, then I will move on from the resistance readings, until some future date.

My car is a 1/76 build and had the A31-060-001 AFM.

It took me a while to get this all down so looks like I missed a bunch of new posts. No time to read them right now. Good luck.

Wow that's interesting experiment guys. I'll help you guys with some data. Just let me get things right in my head.

I won't do any tests on this new one. I don't want to touch it or even look at it. I just want my money back and I'm sorry I bought it now. It's a lot of money for me. I shouldn't have bought it. It was an impulse decision just based on lowest cost and I regret it.

My daily driver is a '94 Camry and it's leaking oil from the valve cover and I am hoping the PCV valve is shot and that I wont' have to change the valve cover gasket. It's got 58,000 miles and a 3.0L. Anyhoo, two compromised cars right now is no fun! hmmmph

xx

Edited February 20, 2011 by Jennys280Z

[Jennys280Z]

Sarah remember I did do the yogurt cup test, at least in the way that I did. I forgot about that. I guess I don't have a leaky intake manifold gasket. *lack of awareness*

One thing I love about my Z is it doesn't leak a drop of anything! *looking on bright side*

[FastWoman]

Sarah remember I did do the yogurt cup test, at least in the way that I did. I forgot about that.

Oh yeah! I forgot too! OK, you're good. I think you've got the valves on your list (which is a satisfying, non-stressful thing, I promise). Put your best non-rebuilt AFM on, get your CTS screwed in, go to Radio Shack for parts, and you'll be good to go.

Here, get these. You can even mail order them:

http://www.radioshack.com/product/index.jsp?productId=2062308

http://www.radioshack.com/product/index.jsp?productId=2062758

Optionally: http://www.radioshack.com/product/index.jsp?productId=2062715

http://www.radioshack.com/product/index.jsp?productId=2049747

http://www.radioshack.com/product/index.jsp?productId=2104090&clickid=prod_cs

Watch this (or any number of other videos):

While you're at it, also order this, so that you can test the potentiometer in your AFM:

http://www.radioshack.com/product/index.jsp?productId=2999093#

The reason you need a needle is that you can see it twitch if you have a dirty electrical contact. You can't see a digital display twitch.

Let's get your car running!

[Jennys280Z]

Wow thank you! I've had a touch of experience with this stuff from school, though never in practice. I am going to practice on some of my PC parts first. I have an old PC that still works, and so will provide a good test bed for my work. I'm scared to use it because I'm scared of lead for one thing. It's just not for me. I probably won't have fun doing it. But having a 280z that runs like new is what the mission is all about.

Your philosophy of how to approach auto repairs is so nice. I might just glide into a great running car here, by fixing one problem at a time, replacing my AFM last, if at all!

OT: Do any of the boardmates here work on Toyotas or know where I can find a good online resource like this website for Toyotas?

[Jennys280Z]

Little update: Python determined instantaneously that my AFM is defective when I read them the numbers.

Which leads to a very intriguing question.

Why did they ship this out, knowing full well that a customer can determine in a matter of seconds that the part is bad, a fact which proves that they can determine in a matter of seconds that the part is bad! What is this? Are they dishonest or are they decadent?

[Jennys280Z]

The AFM looks beautiful. I was heartbroken when I discovered in two seconds flat that I would never install it on my car.

[FastWoman]

I wonder whether they somehow neglected to replace the potentiometer board. I'm sure theirs have resistances all within a tight range of each other, and the resistances you reported were quite different from their normal values.

Don't worry about the lead. Just don't eat it, OK? Obviously wash your hands after handling it. If I were you, I'd just practice soldering on bits of copper wire. That's better than sacrificing working computer parts. Remember, I suggested practicing on boards when I was suggesting a modification to your potentiometer board. There's no need for that now. You won't need much practice anyway. I bet you'll succeed brilliantly in one try. It's that easy.

[Jennys280Z]

I wonder whether they somehow neglected to replace the potentiometer board. I'm sure theirs have resistances all within a tight range of each other, and the resistances you reported were quite different from their normal values.

Don't worry about the lead. Just don't eat it, OK? Obviously wash your hands after handling it. If I were you, I'd just practice soldering on bits of copper wire. That's better than sacrificing working computer parts. Remember, I suggested practicing on boards when I was suggesting a modification to your potentiometer board. There's no need for that now. You won't need much practice anyway. I bet you'll succeed brilliantly in one try. It's that easy.

Okay I won't eat the lead. As for car repairs I already have eaten it compared to most people here

It would be nice to solder my R0 and R10 and just see what happens with that, first. I'll leave pin 7 alone because I'm not sure what to even do around that one.

I have some copper wire from when I did Cozye's TPS test. So you're saying just solder with that? I shouldn't need much. Just a small length of copper wire should be all I need right? Just a tiny penpoint might be enough to do it but I will have to use more than that as I have no experience. I think my dad has a soldering gun he'll let me use.

My newest computer here is 3.5 years old. My oldest one is probably like 15 years old . So working yes, but utilitarian, no.

And yes I need a PC upgrade. Newegg dot com and assembling them myself is fun. I bet you're on a laptop. I've thought about getting one of those for the first time coming up in another month or two.

I cleaned up the water temperature switch ground with WD40 and a nylon brush. I didn't anti-seize this one, which is a rarity for me now. I have learned so much from this website I'm going to make a donation soon!

I'm going to turn my AFM back to stock, or at least what I believe to be stock at the same time that I install my new water temp sensor. I am so hoping to have a better running car.

Has anyone else found the spherical notch on their AFMs BTW? It's easy to look, just pop that black cover off, get a flashlight and look close!

I think I fixed the oil leak in my Camry tonight! It was a stuck PCV valve! And some dipweed took off the clamp on my PCV hose! This would let unmetered air into my engine and worst of all, get dirt in my engine! WTF? And I can see where the clamp was on the hose, but there is NO clamp there. I hope and pray I traded my oil leak for a vacuum leak till I clamp and seal it tomorrow! Installed some GE Nighthawk headlights on the Camry and they're so nice compared to the factory bulbs! Wow! If anyone doesn't like driving at night, I highly recommend them.

Edited February 23, 2011 by Jennys280Z