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Tuning With An Air/Fuel Gauge


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Posted (edited)
1 hour ago, Captain Obvious said:

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?

Gotcha - I originally set mine using the 1400rpm method and haven't fiddled with it yet - but now I know not to!  Ya I was thinking about just bending the lil WOT contact arm a bit but I should have new numbers for you Thursday or Friday night before I fiddle wit it.

My reasoning for wanting to bend the WOT enrichment pin would be that it seems to think freeway driving (3500 rpm) counts as WOT which seems a bit silly to me, no?

The adventure continues haha.

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The TPS has a switch at both ends but only one toggle to rotate....so if  you adjust for the the idle enrichment to drop out earlier, you also cause the WOT enrichment to come in earlier, they both are affected..... you really need an independent adjustment for each of the two switches. It can be fabricated.

Edited by 240260280
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8 minutes ago, 240260280 said:

The TPS has a switch at both ends but only one toggle to rotate....so if  you adjust for the the idle enrichment to drop out earlier, you also cause the WOT enrichment to come in earlier, they both are affected..... you really need an independent adjustment for each of the two switches. It can be fabricated.

I bet that's why my guy bent the vanes with his fingers. :beer:

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3 minutes ago, siteunseen said:

I bet that's why my guy bent the vanes with his fingers. :beer:

Can you pop the cover off and take a picture of the arm spacing?  That would be awesome

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Posted (edited)
2 minutes ago, siteunseen said:

Screenshot_20210317-104929_Gallery.jpg

Wow ya that is a huge difference compared to the pic I put up last night.  I'll get some numbers/rpms for you near the end of the week and then I'll do some bending.  Any idea what RPM you have to hit before it connects to the WOT tab?  I set mine using a multimeter on the bottom two pins and twisted the sensor so that when it got above 1400 the contacts would lose continuity.

Edited by chaseincats
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Just now, siteunseen said:

We have some bad weather coming in the next few days but maybe this weekend I could hook up my timing light that shows RPMs and tell you something then.

Sounds great, thanks!

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10 minutes ago, siteunseen said:

Looking at my picture I can see the middle vane is twisted a little. Wonder if that's what he did for some reason?

That's odd but I don't see how it would change anything.  I thought he bent the main support pin of WOT back.

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I think the gaps can be changed a bit but you really have to alter when the cam (molded in the nylon) pushes on the center vane.

 

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47 minutes ago, 240260280 said:

I think the gaps can be changed a bit but you really have to alter when the cam (molded in the nylon) pushes on the center vane.

 

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Why not just bend it back delaying when the center pin touches it?

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Ok gang, I have some pretty big findings.  Our issue is very much the TPS.

I was driving and getting in the high 13s after leaning it way out.  Frustrated, I pulled over and unplugged the TPS and immediately cruise changed from the 13s to the 17s.  The next plan (probably tomorrow) will be to configure the car to get low 15s (good target?) on cruise with the TPS unplugged, then fiddle with the TPS pins until I am able to get the proper cruise with it plugged in.

The problem very much is a lack of space between the cruise and WOT pin as I was barely able to hold it in the 14s with some really finite pedal work when it was plugged in.

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Great input. Your findings with the WOT contacts are exactly what I meant with my #3 theory:

3) I think the WOT contacts close too early and the car runs too rich when they do.

It's clear from studying the system that the WOT contacts close long before you are actually at WOT. And that's why I was theorizing they closed too soon. But when gas is cheap, emissions standards are loose, and you want to sell sporty cars, you would err on the side of burning some extra fuel instead of the opposite. So going up a hill on the highway closes the WOT contacts. So what? It's just a little more gas.

Butterfly valves (like the throttle plate) are way way non-linear, so even though the plate isn't completely horizontal when the WOT contacts close, I was thinking that maybe you were pretty much there as far as max flow goes. But your A/F readings show that may not be the case.

So what are the alternatives? First alternative I got is the simple one... "Do you really need it at all?" By that, I mean... Can you tune the rest of the system such that the idle looks good, cruise looks good, and WOT is rich enough even without ever closing the WOT contacts?

If not, then the next alternative is what you already mentioned... Bend the WOT contacts as much as you can to delay the closing of the contacts. But as Blue mentioned, you can only do so much with that. Once the cam ramp is over, it's over. And bending beyond that will make it so the switch never closes at all.

If there's still not enough adjustment there, you may want to play around with different cams. That part should be a breeze for someone with a 3-D printer to whip out. Small and not particularly accurate. You could make a custom cam with more rotation between idle and WOT.

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@Dr. 240Z & I were cruising on the highway at 60mph just on the idle circuit of his triple webers (no main jets installed). 

I think you may find the Bosch idle enrichment on the TVS is engaged at cruise as the throttle is opened very little at cruise.

You may wish to attack your optimization this way:

 

1. Configure:  Close AFM idle screw, disable TPS 

2. Set Cruise A/F: Adjust AFM spring to get your cruise at desired A/F ratio

2. Set Idle Enrichment Window: Enable TPS and adjust it so that it is not enriching at cruise. Disable WOT enrichment with tape on its contact as it will now come in earlier.

3. Set Idle A/F:   Use AFM idle air screw to get desired idle A/F ratio

 

You now have optimized 90% of your driving.  Next focus on the WOT (this is "under the rug" where you have swept any challenges from the above first two optimizations).  Perhaps modifying the TPS so that WOT enrichment comes in later is all that will need to be done. Good luck on this final adjustment.

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9 hours ago, chaseincats said:

I definitely think I'll need to keep the TPS switch plugged in in some form as the car drives like a wet shoe without it lol

Well, another idea... I have not looked into any of the details about the actual circuit that performs the WOT or idle enrichment. The rest of the ECU is a black box of analog voodoo magic, and there's no reason to believe the enrichment circuits are anything other than more of the same. And because of that, there exists the possibility the amount of enrichment may actually be able to be adjusted by controlling the amount of resistance between the contacts.

In other words... The system normally works using two different resistance values - zero and infinite. Zero when the switch contacts are closed, and infinite at all other times. But what happens if you use a different value for when the switch is closed. Say 1K Ohms and infinite instead of zero and infinite?

If you put a resistor in series with the WOT contacts maybe it will still actuate the WOT enrichment, but not by as much as when it sees 0 Ohms?

You could try that at idle to see what happens. Compare what the A/F numbers do with 1) the WOT switch open, 2) switch closed, and 3) switch closed with some resistance in series. Just a thought if you wanted to give it a try.

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You would have a blast with a programmable ECU compared to this old Bosch !

When you get the numbers where you want and have recorded your AFR’s - make a valve timing change and see what that does to power and AFR’s . 
 

I’d also say you would be safe to go as lean as 13.2 at WOT if that gives you more adjustment somewhere else . 

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58 minutes ago, Captain Obvious said:

Well, another idea... I have not looked into any of the details about the actual circuit that performs the WOT or idle enrichment. The rest of the ECU is a black box of analog voodoo magic, and there's no reason to believe the enrichment circuits are anything other than more of the same. And because of that, there exists the possibility the amount of enrichment may actually be able to be adjusted by controlling the amount of resistance between the contacts.

In other words... The system normally works using two different resistance values - zero and infinite. Zero when the switch contacts are closed, and infinite at all other times. But what happens if you use a different value for when the switch is closed. Say 1K Ohms and infinite instead of zero and infinite?

If you put a resistor in series with the WOT contacts maybe it will still actuate the WOT enrichment, but not by as much as when it sees 0 Ohms?

You could try that at idle to see what happens. Compare what the A/F numbers do with 1) the WOT switch open, 2) switch closed, and 3) switch closed with some resistance in series. Just a thought if you wanted to give it a try.

@240260280 Good plan, very methodical - I'll do that probably tomorrow evening.  Regarding the tape, I'm guessing you mean just electrical tape wrapped around the WOT contact, right?

@Captain Obvious Interesting idea, I might take that up down the road after everything is setup properly

@madkaw Good to know on the max leanness number for WOT thx

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Ok gang we are at the finish line here - I followed @240260280 's method.  We're sitting at a 15.5 highway cruise with the TPS unplugged, so I cranked the bolt down, put some paint on the current gear tooth for future reference, and shut the cover.  I then plugged the TPS in and set the idle to 14.2 while running at 800rpm.

Now to bend the WOT arm which I will do when it's light out haha.

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Numbers look good. Let's just hope that when the WOT contacts are back in the picture, it doesn't mess things up.

Hopefully you'll be able to bend the WOT out of the way far enough so it doesn't interfere with your cruise numbers.

I was thinking about it just a little more, and another relatively simple idea would be to mount a new WOT switch somewhere else on the system if you needed to. That way you could adjust where the WOT actuated independent of the idle switch. (or vice versa... install a separate idle switch, etc.)

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I still have fond memories of the start of this project cruising in CO's cool purple Z with the AF sensor stuck in the back on the streets of Toronto base lining the L Jetronic. I wish we lived closer together.  Two mad scientists... and more than enough lathes!

 

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

Numbers look good. Let's just hope that when the WOT contacts are back in the picture, it doesn't mess things up.

Hopefully you'll be able to bend the WOT out of the way far enough so it doesn't interfere with your cruise numbers.

I was thinking about it just a little more, and another relatively simple idea would be to mount a new WOT switch somewhere else on the system if you needed to. That way you could adjust where the WOT actuated independent of the idle switch. (or vice versa... install a separate idle switch, etc.)

Interesting idea - we may go that route depending on how the bending goes.  One final question, am I bending the thin copper arm (noted as "1" in the below picture) or the thicker grey metal arm (noted as "2" in the below picture)?

UPDATE: I bent #2 and using a multimeter to test the wot pin I'm now getting WOT continuity at 3/4 pedal pressure instead of 1/4 lol.  I tried to bend it back to get WOT at 2/3 but it doesn't really want to go back in place.  Either way, I'm happy with this and will report back on the driving dynamics/numbers tomorrow night.

IMG_7551.JPG

Edited by chaseincats
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