1977 280z prepup for smog check

[240zadmire]

@Zed Head will go pickup the 78 fuel rail with included FPR this weekend.  Hopefully it is in good working order.

29 minutes ago, Dave WM said:

just for grins, remove the fuel return line for the metal hard line that goes to the tank, and just have it dump into a container.

this is an excellent idea.  Will looking into this. 

Thank you for sharing great info gentlemen.

 

regards

[Patcon]

Okay, I am playing around in areas above my pay grade but why not add a rheostat somewhere discretely, maybe behind the glove box to lean it out a little? We know these old parts tend to drift rich over time

[S30Driver]

1 hour ago, Patcon said:

Okay, I am playing around in areas above my pay grade but why not add a rheostat somewhere discretely, maybe behind the glove box to lean it out a little? We know these old parts tend to drift rich over time

If you are talking about the coolant temp sensor circuit to the ecu Charles, then if the circuit and sensor are working properly - adding resistance to the circuit with a rheostat will only add fuel.  The ecu will think the coolant is colder and compensate with more fuel - make it richer.  Unfortunately, you can't go the other way - leaner, unless you were to adjust the afm to a lean condition beforehand in an attempt to get the pot somewhere in the middle of its range and then you could adjust the mixture up and down accordingly.  

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

[240zadmire]

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 !

[Dave WM]

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 October 9, 2020 by Dave WM

[Zed Head]

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

[SteveJ]

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.

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).

 

[Zed Head]

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

[Zed Head]

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.

[Zed Head]

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.

 

[Zed Head]

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.

Edited October 9, 2020 by Zed Head

[240zadmire]

@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 October 9, 2020 by 240zadmire