Tuning With An Air/Fuel Gauge

[chaseincats]

11 minutes ago, Captain Obvious said:

What a coincidence... I didn't have any pics of my evap system to refer to aid the discussion, so I popped the cap off mine and took some pics too.  Haha!!

So, I bet I know what's going on with yours... I had mentioned earlier that there's not much to it. A diaphragm, a spring, and a metal ring seat for the spring. Well, you're missing the metal ring seat for the spring. I believe it's purpose is to keep the end of the spring a metal surface to press against to even out the pressure and keep the sharp pointy metal end of the spring from poking through the soft rubber diaphragm.

Well you don't have the seat, and my guess would be that your spring has poked a small hole through the diaphragm. Inspect carefully at the dent where you can see where the spring was pushing:

In any event, it's supposed to look like this:

And I also verified that my small control line does hold vacuum.

About attaching the large line directly onto the post down inside the cap where the spring lives? I think your assessment is correct. It'll be continuously purging at all times. Probably just fine at everything but idle. At idle, you might find it runs it lean again. I don't know if you have enough compliance travel in the mixture screw to compensate, but if you're just looking for an option to try until you can find a new can (or at least diaphragm and spring seat) it's worth a try.

If you find you can compensate with the idle mixture screw, you should be fine.

I went to a local junkyard today that has some of these cars and grabbed a ring and diaphragm (you are absolutely right - there was a pinhole poked through where that dimple is).  While I was there, I brought my vacuum hand pump and tested the cars on the lot.  A bunch of them (mine now too) held vacuum on the larger lower hose but none held vacuum on the upper smaller one even though the diaphragms looked good...

[Captain Obvious]

Well I'm not sure I have an explanation for which hoses hold vacuum and which ones don't, but it sounds like your EVAP should be in better shape now than it was before.

So, looking at that carbon canister cap valve thing... Notice how the spring pushes the valve into the open (purge) position. Also notice how the control vacuum line (smaller upper) pulls the valve into the open (purge) position. The question I can't easily answer is "The control line pulls the valve from above to open it. But the valve is already being pushed open by the spring from below. So what is it that ever CLOSES that valve?"

And that's where the theory of the high manifold vacuum helping to pull that valve closed comes into play.

So when do we get the next round of A/F readings now that you've fixed the cold start injector and (hopefully) the EVAP stuff?     

[chaseincats]

17 minutes ago, Captain Obvious said:

Well I'm not sure I have an explanation for which hoses hold vacuum and which ones don't, but it sounds like your EVAP should be in better shape now than it was before.

So, looking at that carbon canister cap valve thing... Notice how the spring pushes the valve into the open (purge) position. Also notice how the control vacuum line (smaller upper) pulls the valve into the open (purge) position. The question I can't easily answer is "The control line pulls the valve from above to open it. But the valve is already being pushed open by the spring from below. So what is it that ever CLOSES that valve?"

And that's where the theory of the high manifold vacuum helping to pull that valve closed comes into play.

So when do we get the next round of A/F readings now that you've fixed the cold start injector and (hopefully) the EVAP stuff?     

Haha those numbers will be coming late afternoon.  I'm going to run/tune it the evap disconnected later today - that way we take the potential vacuum leak out of the equation.  Once it's set, I'll reconnect evap and see if the numbers change with it connected probably on Thursday.  We're so close I can taste 14.7 lol

Just to confirm, ideal would be this, correct?:

• Idle: 14.2
• Cruise: 14.7
• WOT: 12.3

Edited March 10, 2021 by chaseincats

[Captain Obvious]

I'm no expert on the topic, but from what I've heard the numbers you listed as your goal would be excellent. Maybe cruise just a little bit leaner? I guess that depends on how likely the engine is to incur pre-ignition, right? If it's an engine that's designed "not to ping", then you can run leaner?

Anyway, there are guys here on the forum much better versed in that stuff than I am.

As for the plan about testing with the EVAP completely plugged off and then again with it connected... I think that's an excellent idea. That'll give you an idea of what's going on. In theory, the only change you should see is that your cruise number should get a little leaner with the carbon can connected.

[chaseincats]

Well here's something interesting - I took the cap/diaphragm out last night to glue a tiny pinhole and now the bottom hose port not longer holds vacuum but the top now does.  I think I'm going to plug the big hose directly into the canister and end this back and forth with the can.  

Edited March 10, 2021 by chaseincats

[madkaw]

On 3/9/2021 at 11:19 AM, Tweeds said:

A little off topic here - is it stock for the A/C stuff to be backlit like that? If so, mine never have been. The panel doesn't look stock to my eye - I don't recall it being so shiny, but, then again, maybe I'm not very observant. 

On topic - been following the thread and it's had a lot of interesting information, discussion, and graphs. Great stuff!

That’s a 73 heater panel that had the backlighting 

[Tweeds]

1 hour ago, madkaw said:

That’s a 73 heater panel that had the backlighting 

Ah! I've got a '71. It's a nice little touch - changing the settings in the dark is not too easy without being able to see what you're doing.

[chaseincats]

8 hours ago, Captain Obvious said:

I'm no expert on the topic, but from what I've heard the numbers you listed as your goal would be excellent. Maybe cruise just a little bit leaner? I guess that depends on how likely the engine is to incur pre-ignition, right? If it's an engine that's designed "not to ping", then you can run leaner?

Anyway, there are guys here on the forum much better versed in that stuff than I am.

As for the plan about testing with the EVAP completely plugged off and then again with it connected... I think that's an excellent idea. That'll give you an idea of what's going on. In theory, the only change you should see is that your cruise number should get a little leaner with the carbon can connected.

So I took it out, unfortunately there was traffic but after fiddling with it I definitely have control over the idle again.  I really moved quite a few teeth on the black gear (maybe 13?) and got the car to cruise at 14.7 but it did really feel anemic so I dropped it down a few teeth.  That said, there really was too much traffic to get reliable numbers so I think I'm going to put this on hold until the weekend when I can take it on the highway and get better numbers for you folks.

[Captain Obvious]

9 hours ago, chaseincats said:

now the bottom hose port not longer holds vacuum but the top now does.

That's what mine does. And looking at the valve, I think that's what is to be expected.

Good luck with the weekend tests and let us know what you find.

[chaseincats]

When adjusting the throttle position sensor (TPS) I'm seeing two schools of thought.  One says the idle enrichment arm should be connected to the middle contact until 1400rpm (atlanticZ) and a bunch of other folks saying the idle enrichment contact should disconnect once you hit the pedal which makes more sense to me.

Any ideas?

I found this thread which discusses it: https://www.classiczcars.com/forums/topic/25240-tps-adjustment/

[madkaw]

It is just a switch , not a true TPSensor. Not sure if it will make a big difference either way . I would shoot for contact movement 

[chaseincats]

8 minutes ago, madkaw said:

It is just a switch , not a true TPSensor. Not sure if it will make a big difference either way . I would shoot for contact movement 

Right, but what I mean is AtlanticZ says that throttle movement up to 1400rpm should be counted as "idle" which sounds strange.