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Tuning With An Air/Fuel Gauge


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Posted (edited)
20 minutes ago, Captain Obvious said:

Yes, I mean RTV.

I'm particular to "Permatex Ultra-Grey" because I've found it to be the firmest (highest durometer) once cured. And in this application where you're trying to seal that flimsy, probably already bent flange using a thin paper gasket, I think the high firmness is especially valuable. It's not really gasoline rated, but in this application, I would still use it. If everything is working as intended, that gasket should be a seal for air, not gas.

I don't think a dry paper gasket is going to get you where you need to be.

I wanted to avoid that stuff but if you think that's the only way then I'll go grab some.  You need to wait 24h before starting the car, right?  As a sidenote, could it be that since my gasket doesnt have the other side of the screw holes, the screws are bowing it out, creating the leak?

EDIT: Do you think its possible to fix my carbon canister's leaky vacuum valve?  Are these even serviceable?

Edited by chaseincats
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10 hours ago, chaseincats said:

I wanted to avoid that stuff but if you think that's the only way then I'll go grab some.  You need to wait 24h before starting the car, right?  As a sidenote, could it be that since my gasket doesnt have the other side of the screw holes, the screws are bowing it out, creating the leak?

EDIT: Do you think its possible to fix my carbon canister's leaky vacuum valve?  Are these even serviceable?

Well that gasket in your pic is (the technical term) "trashed". Even if you weren't going to use any RTV, there's absolutely no way you should reuse that gasket. Not only does it create an uneven mating surface under the bolts (potentially bowing the flange as you mentioned), but it's also permanently compressed.

So in your shoes, if you really don't want to use RTV, you could always try a new gasket first (without RTV) and check it with you A/F meter. If you don't get satisfactory results, you could take it apart again and goop it up.

I'd never been a fan of any sort of gasket compound either, but now I put it on just about everything. I hate seeing big gobs of sealant squeezed out of the gap and I always thought of it as a crutch for people who didn't know how to do things right. Then I started working on lawn and garden carbs where I just couldn't get stuff to seal. So I started putting a little on with a syringe. Just a tiny bit. Now I put a tiny bit on most everything.

And yes... you should give the RTV some cure time before you stress it. Heat helps, so if you put it on your motor while it's still warm from running, it should be good to go the next morning.

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Forgot about the valve on the CARB can... There's not much to it. A diaphragm, a spring, and a metal ring seat for the spring. I looked through my pics for something that might show the guts, but I got nothing. If the diaphragm doesn't have any holes in it and is installed correctly (not folded over), then I don't know what else to do there.

Does the control line (smaller line shared with the distributor advance) hold vacuum?

I do remember someone doing some testing on the valve... @Dave WM   maybe?

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1 hour ago, Captain Obvious said:

Forgot about the valve on the CARB can... There's not much to it. A diaphragm, a spring, and a metal ring seat for the spring. I looked through my pics for something that might show the guts, but I got nothing. If the diaphragm doesn't have any holes in it and is installed correctly (not folded over), then I don't know what else to do there.

Does the control line (smaller line shared with the distributor advance) hold vacuum?

I do remember someone doing some testing on the valve... @Dave WM   maybe?

It seems neither inlet holds vacuum well.  While the big hose's end won't hold vacuum at all, the smaller hose's valve can be pumped up with my hand-held vacuum gauge but the needle quickly falls after you stop pumping.

I did try running the car last night with the large hose plugged into its intake manifold port (I didn't have the smaller one plugged in for whatever reason) and sprayed the canister's valve with starter fluid to see if the engine idle changed but oddly it didn't.  How can it be leaking vacuum but not raise the engine idle when sprayed?

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9 hours ago, chaseincats said:

It seems neither inlet holds vacuum well.  While the big hose's end won't hold vacuum at all, the smaller hose's valve can be pumped up with my hand-held vacuum gauge but the needle quickly falls after you stop pumping.

I did try running the car last night with the large hose plugged into its intake manifold port (I didn't have the smaller one plugged in for whatever reason) and sprayed the canister's valve with starter fluid to see if the engine idle changed but oddly it didn't.  How can it be leaking vacuum but not raise the engine idle when sprayed?

The small canister hose should hold vacuum at all times. If it doesn't you might want to pop the cap off the carbon canister and have a look around.

The big canister hose will not hold vacuum with the engine off. And that's my little bit of confusion about the system. The FSM talks about the large line as being sealed until the control lines opens it, but in my experience, that is not the case. My theory (that I talked about a little earlier) is that the high vacuum source pulled directly from the intake manifold actually helps pull that large line into a closed position.

As for the other question about not changing the idle... It's probably because that small line (and the distributor advance) is pulled from a ported vacuum source. And at idle, there's no vacuum so nothing gets pulled into the intake tract. In other words, it's not a vacuum leak on that throttle body nipple unless the throttle blade is in a specific position. At idle, there's no vacuum, and at WOT there's no vacuum. The only time there is vacuum there is at a light cruise position.

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14 hours ago, madkaw said:

Doing my own wide-band tuning today . Two are better than one !

726FD899-AC76-4DD0-B3DC-7C6A965509C0.jpeg

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!

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Posted (edited)
10 hours ago, Captain Obvious said:

The small canister hose should hold vacuum at all times. If it doesn't you might want to pop the cap off the carbon canister and have a look around.

The big canister hose will not hold vacuum with the engine off. And that's my little bit of confusion about the system. The FSM talks about the large line as being sealed until the control lines opens it, but in my experience, that is not the case. My theory (that I talked about a little earlier) is that the high vacuum source pulled directly from the intake manifold actually helps pull that large line into a closed position.

As for the other question about not changing the idle... It's probably because that small line (and the distributor advance) is pulled from a ported vacuum source. And at idle, there's no vacuum so nothing gets pulled into the intake tract. In other words, it's not a vacuum leak on that throttle body nipple unless the throttle blade is in a specific position. At idle, there's no vacuum, and at WOT there's no vacuum. The only time there is vacuum there is at a light cruise position.

So I went downstairs and popped the cap off the canister and took a couple of pictures of what I found.  The diaphragm doesn't seem to be torn so I flipped the diaphragm over and put the cap back on (pictured is how it was originally) to see if that was the issue then tried my vacuum gauge but it sounds like vacuum is escaping around the cap.  Any ideas?

EDIT: the diaphragm was leaking around the sides and had some small tears.  Since these are nla, can I just plug the big hose directly into the top of the canister?  That would kill the on-demand part from the throttlebody but would that allow the canister to still function?

unnamed.jpg

unnamed (1).jpg

Edited by chaseincats
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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:
chase1.jpg

In any event, it's supposed to look like this:
P1180755.JPG

P1180756.JPG

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.

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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:
chase1.jpg

In any event, it's supposed to look like this:
P1180755.JPG

P1180756.JPG

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...

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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?      :geek:

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Posted (edited)
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?      :geek:

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 by chaseincats
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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.

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Posted (edited)

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 by chaseincats
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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 

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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.

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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.

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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.

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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/

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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.

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Posted (edited)
26 minutes ago, Captain Obvious said:

I just published my book report in that other TPS thread.   LOL

Awesome, I'll respond in there, thanks!

Brief update - I didn't drive the car at all this past weekend as I left my gauge powered up when I scampered up the stairs to write the previous numbers post which subsequently drained my battery when I went to start it a few days later lol.

I got the car going in the driveway today and noticed that with the car set as lean as it is, my idle speed dropped to around 450, so I brought that back up to 800 and the idle is sitting at around 14.7.  The idle air bypass screw is indeed turned all the way in and the only way to lean out the idle further is to retard the black gear.  I think at this point, that is just how it will have to sit.

When playing with the throttle, I noticed in cruise mode it will sit in the mid 15s and pushing the linkage to when the WOT pin connects on the TPS, brings the gauge to the mid 12s which all look really good (although when the car is under load I'm expecting the numbers to change a bit).

That lead me to the TPS configuration question because it seems that the cruise mode leanness only lasts a short amount of pedal travel - maybe only an inch or so.  I can check tomorrow at what rpm the WOT pin connects in the TPS if that information would be of some help?  I attached a picture of my TPS but its in a different orientation because of the weber throttlebody.  The bottom pin in the WOT pin - should I bend it down somewhat?

IMG_7551.JPG

Edited by chaseincats
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I suspect the reason for the change in your numbers are simply from different engine temperatures. If you tuned it all nice and warm and then shut it off and now you notice that the numbers are way different on a cold start, I bet that's what's going on.

I talked about it a little in the TPS thread, but to bring some of that here as well... I don't think you can apply any meaningful info to the WOT setting of the switch unless the engine is under load.

I haven't connected an A/F gauge to my car, but my seat of the pants "feelings" about the Bosch L-Jet system after messing with it some:

1) The slope of the enrichment from cold to warm is too steep. In other words, it's too rich when cold. You could set it "correct" when cold, but then it'll be lean when warm.
2) The impact of the air temp sensor in the AFM is too high. Sort of the same thing as above. When the incoming air is cold, it runs rich.
3) I think the WOT contacts close too early and the car runs too rich when they do.

The bottom line is it's an analog system designed in the early seventies when gas was cheap and performance was higher priority. No computer, no feedback, and no tuning features.

I think the numbers you were getting earlier in this thread are fantastic and I think you might be trying just a little too hard with the RCH adjustments of the throttle switch?   LOL Set the TPS using the 1400 RPM method, and get idle and cruise working again. Then lets see what the WOT numbers look like. Maybe we can entertain some modifications to the TPS to close the WOT contacts deeper into the pedal?

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