I posted something about this last week.

I had an o2 sensor and bung welded into my collector this afternoon.

Using a voltmeter and some information posted on the other thread, I was able to get a fairly good read on my mixture. I thought something was wrong but it turns out I was running a bit lean (between 15.5/1 and 16.0/1 at idle)

After doing some adjustments I wanted to be able to get a good read at idle and cruise. Here's where I am now:

approx. 14.7/1 @ 1000 rpms
approx 14.2/1 @ 3000 rpms

Does this sound OK? Do I want to go a bit leaner or a bit richer? Any other ways I want to think about this test procedure?

Thanks!!

Hmmm, Lars told me that I should be closer to 13:1. Said that even 13.2 - 13.6 is a touch on the lean side. But that was at WOT througout the curve. Not sure what it should be at idle.

So I should think about going even richer?

14.7:1 is the perfect stoichiometric ratio. That's a bunch of chemistry mumbo-jumbo (I'm a EE/Comp E) that means that the "best" burnable ratio of gasoline to air is 14.7 parts air and 1 part gasoline. So, you're looking good on a "clean combustion" side.

My understanding of talking to Lars and others is that max power is actually made at a slightly richer setting of approximately 13.5:1.

With 14.7, you'll make good gas mileage, and that's what the EFI computer's goal is in a new car...it adjusts the duty cycle (on/off time) of the fuel injectors based on the "goal" of 14.7:1 in any situation.


Hope this helps. :smash:

I'm sure there's a number of factors to consider. But at cruise, many say the mix can be / should be between 15 and 16 to 1. Matter of fact, the Edelbrock carb manual still says that.

I didn't test the A/F voltage at cruise, only at idle where it appeared to be a bit lean (or so I thought). Now I have conflicting info on which way I should go... :crazy:

Are you using a wide band sensor? If not, you can't use it for tuning a carb engine.

A standard sensor is only fairly linear just around 14.7. I practice, it can only show if you are running lean or rich.
It's more like on/off and you cant get any meaningful reading with a digital DVM.

I made a custom vaccum/dual O2 meter. It's fun to watch, but as said, it's basically on or off.
Did this since I will install TPI later. With a closed loop system the display will show how the computer is adjusting the ratio.

There are plenty of info on this if you subscribe to the diy-efi.org list. You also find an easy to make O2 meter circuit at the diy-efi.org site.

Ingar buddy
sorry to hear you fell for that ivory tower engineer b.s. http://community.webtv.net/MATTGRU/AFtesting

Which engineer are you refering too?
I would love to be able to tune my engine with what I have.

But there must be a reason for people paying $1000 for a WB-sensor and make a special display for it? (If you are a member of that mailing list you understand what I mean...).
Thanks for the link, I study that.

Bragging rights is my guess. Both myself and a friend with a 302 Mustang do just fine tuning with our $15 over the counter "narrow-band" O2 sensors. :smash:

It's interesting because it seems to me that the display works pretty well. I bought a $30 Bosch O2 sensor, and once it warms up it gives pretty good readings. Certainly it's consistent, and it I could tell I was running lean and adjusting the mixture screws gave pretty good immediate feedback.

I have no doubt that running a really expensive setup would give me better resolution, but I'm not tuning the car for the track. :)

Still, assuming this is better than just guessing, it would be helpful to know what A/F I'm shooting for!

:cheers: :smash:

Hey guys,

I wanna play too... :D What kind of O_2 sensor should I get, and what A/F meter would you recommend? (Keep in mind I'm on a tight budget... :))

Thanks,
-Pedro

[Edit] seems that Albert already answered one of my questions... :D[/Edit]


[Modified by Pedro'74, 1:51 PM 3/31/2002]

I just asked for an off-the-shelf 2-wire O2 sensor. I'll post the part number later today. Cost me $32 for the sensor and $30 for the bung and weld.

BTW - Happy Easter! :seeya

Thanks, Albert! Happy Easter! :)

-Pedro

What do you want? Power or economy?

Power: 13.5
Economy: 14.7

You can also tune the idle circuit for 14.7 and then the power/accel circuits for 13.5, possibly still getting your cruise circuit at 14.7...

I got 10 of them for a buck a piece. Not only that you can get the heated sensor type...ensure that you pick up the plug in connector for each one. I got my 10 (all off Fords) in case one of them was bad.
Here's a website that sells an analog gauge (or a whole kit). The website also has the wiring instructions.
http://www.cbperformance.com/catalog.asp?ProductID=598

Power is good :)

I'll try richening it up a bit and see how that works!

Thanks guys!

FYI - the part number for the o2 sensor wad 12028

Ok, I understand there are different opinions on this. What I wrote was just an impression after following the discussion at diy-efi.

At least my instrument is basically on or off. (I use two 4-wire heated sensors, one at each header collector)

It's very simple to make your own LED gauge, an LM3914, 10 led's and two resistors are all you need.

I found this image that shows the voltage output as a function of the air/fuel mix. As can be seen it's pretty steep in the middle region...



[Modified by Ingar, Norway, 4:16 PM 3/31/2002]

OK I see your point.

To be honest, the readings I was getting had much better resolution in the middle area, as your chart shows.

I wouldn't say the switch is ON/OFF, but you certainly get more specific readings in the middle. I was getting strange readings at first and I thought this wasn't going to work. Then I realized that I was running REALLY lean, and as I slowly adjusted the mixture screws the readings got better and more consistent.

That said, probably for the bulk of the people on the forum, just getting good readings in the middle would be a great start, esp. for about $50. You can at least be accurate about how far off you are. For REAL performance tuning you'll want to be on a dyno anyway. For garage tuning, I think this has been great.

The high 12/low 13 readings are desirable at wot but not for cruise. At other than wot, you're only wasting fuel, increasing carbon build up, and washing down cylinder walls. That's why carbs have different circuits for different conditions.