1977 280z prepup for smog check

[Zed Head]

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.

[240zadmire]

@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

 

[Dave WM]

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 October 9, 2020 by Dave WM

[Zed Head]

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.

[240zadmire]

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

 

[Dave WM]

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.

[240zadmire]

You have a lot of toys, wish I could be your neighbor kikikiki

 

need more reading to whether to screw in or out ....

[Dave WM]

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 October 10, 2020 by Dave WM

[240zadmire]

@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 

[240zadmire]

Sound like there is a high tension spring inside the switch.  Gently hitting it on your palm can be heard the tension of the spring 

[Zed Head]

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...

Edited October 10, 2020 by Zed Head

[Zed Head]

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.