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1977 280z prepup for smog check


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39 minutes ago, S30Driver said:

I wish my old bank account drifted richer over time ...

Don’t we all!? But again, some say money won’t bring happiness.  I just need enough so that when the deliver guy knock the door or when wife looks at the billing statements, she won’t freak out, too much.  
 

I’m very close.  Everything seem to be within specs.  The FPR is a bit out is spec as noted by ZH and in the FSM.  I’m pretty confident the vacuum is tight.  The questionable one might be the EGR pipe from the intake to the exhaust manifold.  I broke the original one and luckily to found the 78 one.  I had to put an adapter thread to connect to it.   I will check again at that area.  
 

I’m soooo close to legally driving my car.  To experience the loudness, the smog residue on my cloth 😉 and especially the adrenaline rush the wheel might fly off at 70mph on freeway. 😉 so exhilarating !

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you could hook the rheostat in P with the coolant temp sensor vs series. that would allow you to make the resistance lower (could even just disconnect the sensor completely that way, and just use the rheostat like a choke lever. the issue is I think below a certain resistance the ecu does not lean out any more. that is a guess based on the idea that it ignores the input from the sensor once its over 140f.

If you decide to hook up in parallel you would want a higher value since leaving the sensor in circuit will cause a lower resistance. something like a 10k would be so high that maxed out it would not reduce the resistance too much for normal operation. It would make the circuit some what more critical in how the range of the pot would work. 

Prob best bet would be just hook up the rheostat of about 3k-5kin place of the sensor and use it like a manual choke. that would allow you to manually mimic the operation of the sensor.

A fun example is using a pot like this and a color tune plug so you can actually see the effect. I did something like this on my spare engine that is mounted to a test stand.

Edited by Dave WM
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I think that using a parallel circuit flattens the curve, whereas a series circuit moves the whole curve up.  The ECU expects a certain curve rate.  Probably create new problems.

CO and SteveJ probably draw charts in their heads on this kind of stuff.  @Captain Obvious @SteveJ

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1 hour ago, Zed Head said:

I think that using a parallel circuit flattens the curve, whereas a series circuit moves the whole curve up.  The ECU expects a certain curve rate.  Probably create new problems.

CO and SteveJ probably draw charts in their heads on this kind of stuff.  @Captain Obvious @SteveJ

Are you referring to when CO and I were discussing the GM coolant temperature sensor vs the Nissan cylinder head temperature sensor? That was when I was prepping for the fuel injection conversion on the 260Z. 

As @Zed Head pointed out, the curves for these sensors are not linear.

CHTS resistance curve.jpg

For the CHTS, a resistor in series would keep the curve from moving the left. It would essentially stall out at the value of the resistor. A resistor in parallel would move the starting point of the curve to the right, but the effect could be diminished as the sensor resistance drops if the value of the external resistor was high (needed to keep the curve from starting too far to the right).

 

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14 minutes ago, SteveJ said:

Are you referring to when CO and I were discussing the GM coolant temperature sensor vs the Nissan cylinder head temperature sensor? That was when I was prepping for the fuel injection conversion on the 260Z. 

No, more that you guys just have a better feel and familiarity with the equations.  I had a vague feeling so plotted some numbers to be sure, but generally, practice makes better.  Thought you guys might verify or have an opinion.  Not one of my fortes.

It was a good reason to rummage around the internet though.

https://www.swtc.edu/Ag_Power/electrical/lecture/parallel_circuits.htm#:~:text=The sum of the currents,1%2FR3 %2B...

https://www.swtc.edu/Ag_Power/electrical/lecture/series_circuits.htm

https://www.swtc.edu/Ag_Power/electrical/lecture/ohms_law/ohms_law.htm

https://www.swtc.edu/Ag_Power/electrical/lecture/combo_circuits.htm

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I was reading Dave WM's Pikes Peak thread and realized that you might have an altitude switch.  Keep it in mind if you can't get the FPR change to work, or try it before hand if you don't want to swap rails.

image.png

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Here's the post that mentions it.  You might have the switch that you can jump or might just have an ECU that will drop fuel by 6% if you short the pins.  Keep it in mind.

 

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The wiring diagram says it's in the cabin.  Probably under the dash by the EFI relay.

There's been a lot of talk about it but I've never seen anyone actually use it.

image.png

image.png

Edited by Zed Head
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@Zed Head, @Dave WM et all,

 

yes, there is an altitude thingy dangling/mount under the steering wheel.  I will take a look at it later.   very interesting to learn at different altitude the car behave differently.  Where I live, the elevation is about 490 feet.

Why California models always have this "special" treatment.  Other states don't have hills/valleys?

 

regards

Edited by 240zadmire
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California was ahead of everybody else on emissions.

If the thing has a port or opening on it you should be able to just suck on it and fool the ECU in to thinking you're at high altitude.  You should hear a change in engine idle if it's running.  Easy test.

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@Zed Head thanks for the pointer.  Look like I need to make a jump from pin 9 and 12 to turn the altitude “ON”. The idle should lower a bit. Does that affect the RPM?  If you need to maintain 800RPM, don’t you need to advance it a degree to compensate? Then what are we trying to achieve ?  I’m sorry, I’m (a lot) dense.  Please explain

 

thanks

 

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trying to lean out the mix to lower CO, the alt switch may be the ticket as a work around. If its working you may notice a higher rpm due to leaner mix at idle.

Edited by Dave WM
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I'd just unplug it and jump the plug.

Like Dave said.  If it works there will be 6% less fuel so the air-fuel ratio will be leaner.  Should be enough to get you past the test.  It might even run better and you can just leave the 40 psi FPR on and drive it that way.  The ECU will just think you're in the mountains.

But, if it were me, I'd try to understand the switch better first.  Just to be sure that it doesn't have some internal resistance.  Remove the switch and find a way to actuate it if you can.

It's just an option.  My car didn't have one otherwise I'd know more about it.

image.png

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31 minutes ago, Zed Head said:

My car didn't have one otherwise I'd know more about it.

well, you'll need to buy another car with all sort of California "junk" on it, so you can help all of us out 😉

it's 5 pm  on Friday and I'm still at work. aaaahhhh

 

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one of my plans was to hook a scope to the injector and observe the duty cycle, see what sensor effect actually look like. This is one of the test I wanted after my failed attempt at getting to the top of pikes peak. Been busy with other stuff so have not gotten around to this test. I will try to see if I can find out the effect of the alt switch this weekend, I don't think my current harness is set up for it so I eill have to see if I can get work around to get wires to the correct ecu pins and try it out.

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that would be fun to play with. hook up to a continuity test, then inside a sealed camber, pull a vacuum and listen. See how deep you have to go to activate, then I presume you could compare that to a air density chart to confirm what altitude triggers it. I assume there are other variables (temp, humid). still just checking to see if it works would be fun.

Edited by Dave WM
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@Dave WM my dad was a hard working farmer, retired many years now.... And I don’t make that much money... kakakakaka.  All of these toys are out of my reach.  I don’t even know what they are let alone their usage 😉. Learn new thing every day.... this is what I’m going to do, while car is in idle, hot jump the wire.  Hope I won’t screw other stuff 

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35 minutes ago, 240zadmire said:

while car is in idle, hot jump the wire.  Hope I won’t screw other stuff 

I would wait on that.  If there's a spring and an adjustment screw it might not actually be an on-off switch.  It might be a potentiometer that varies resistance by atmospheric pressure.  If it doesn't go to zero résistance you might short something out in the ECU.

It had been in the back of my mind that it would be odd to have a switch that made a dramatic on-off change at a certain altitude.  Your observations kind of made things more clear.  It makes more sense that it would be a variable pot.

So, you might be able to put a potentiometer in its place.  If somebody wants to study the AFM pin-out and see how resistance on that circuit affects the signal to the ECU, feel free.  Pin 9 is one of the legs of the AFM potentiometer.

My brain is starting to hurt...

image.png

Edited by Zed Head
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I think that I would unplug it first and see what happens.  That would be open circuit, super-high resistance, just like an ECU without an altitude switch.  

Then connect a potentiometer, set to open circuit/high resistance and carefully dial in some parallel resistance and see if you get a change.

A new puzzle.  Yay.

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@Zed Head 

34 minutes ago, Zed Head said:

My brain is starting to hurt...

Your brain cannot go on holiday right now!

There is a screw at the end.  For sure it is for adjusting.  And there is a lock screw with a white paint marked.  I suppose that is a lock screw and was set at factory.

 

the wire schematic showed like a switch... but you already know what is it. Very interesting.  I’m glad the problem give you some challenge.  I have zero clue 😉 

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maybe its been covered already, but does the car have a cat? if not just adding one maybe a simple solution. If it has an old one, perhaps it needs to be replaced? I don't know how you would test it for effectiveness, only if its clogged or not.

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About the altitude compensator... All of the documentation I have indicates that the altitude compensator is an ON-OFF switch affair, and not an analog resistance device. I don't have one of those devices here for confirmation, but that's what the docs say. (Ref 77 FSM EF-15 and the 1980 FI bible page 85.) I wouldn't worry too much about a dramatic change in engine operation when the switch changed state. They can handle that in the electronics with smoothing and hysteresis.

As for the stuff inside the altitude switch... Don't knock that thing around too much. That "spring" inside is actually a hermetically sealed bellows chamber. It's very similar in construction and operation to the bellows in the throttle pull-pull off and the BCDD.

Here's a thread that's about the BCDD, but there are some good pics of the BCDD altitude compensating bellows that they used inside there. Looks like this:
IMG_2456.JPG

IMG_2457.JPG

Here's the thread where those pics came from:
https://www.classiczcars.com/forums/topic/58748-info-on-bcdd-boost-controlled-deceleration-device/

 

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2 hours ago, Captain Obvious said:

About the altitude compensator... All of the documentation I have indicates that the altitude compensator is an ON-OFF switch affair, and not an analog resistance device. I don't have one of those devices here for confirmation, but that's what the docs say.

So you're saying that he should trust what the FSM says and go ahead and short that switch?  Assume that a direct short is fine and won't harm anything. 

Here's the post with the image showing the switch-like behavior.

 

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