MicroSquirt.com read only forum (Jan.15,2018)

When setting up req. fuel there seems to be a wide gap at stoich. For instance, at fast idle 1000rpm, with req fuel set at 12.0 the EGO indicates 0.76. Reducing the req fuel gradually it start to drop until it goes down to 0.65 at 11.6. From there on the EGO will swing back and forth until I take the req fuel down as far as 9.6 when the EGO will settle around 0.35. The idle quality degrades about halfway throughout this transition. Lowering the req fuel further drops the EGO to stick on 0. At what point do I assume that I have reached stoich?

Having read lots of other stuff here I undertsand that the EGO readings can swing back and forth at near stoich but my confusion is how this can be tuned effectively. How can I get the mixture right if I don't know the crossover point? How can programmes like MSTweak find the right points if the EGO is all over the place?

I can't make any sense of this. Am I missing something obvious? Am I being a bit dense?

Bob, you have to try and think of the narrow band sensors as essentially a binary device with two states - either richer than stoich (> .5v) or leaner than stoich (< .5v). It cannot, with any degree of accuracy or repeatability, tell you how much richer or leaner. They are great for finding and maintaining a stoich at cruise condition, that is their OEM function. Most vehicles will not idle well, if at all, at stoich.

-Mike

Bob,
The swing is what MSTweak uses. When it starts swinging, your close to stoich.

Thanks for the help guys but my original question was at what point do I assume that I have reached stoich?

As I said, I have a very wide band between when the mixture settles rich and when it settles weak and in between it swings back and forth. At what point in the middle do I assume stoich?

Do I go rich and inch it down until it swings or go weak and inch it up until it swings? Somewhere in the middle? Another way?

Interesting that MSTweak uses this swinging band but where does it decide the best point to adjust to?

Can you see what I mean or am I asking stoopid stuff? Is there a definitive guide somewhere I can learn about this in more depth other than the help in Megatune and MSTweak?

Sorry for lots of questions but I've only just started tuning and am having difficulties making sense of it all. At the moment my car idles OK but drives like sh*t!

bobtoke,

Instead of using the 'raw' sensor voltage, use the EGO correction as your guide. It is 'damped' to give a better indication of the average sensor reading under any given conditions.

So you've reached stoich when the sensor switch voltage is right for your sensor, and the EGO correction is 100%.

Lance.

Hi bobtooke,
My comments are embedded
Sunday, January 30, 2005, 6:51:47 PM, you wrote:

b> At what point in the middle do I assume stoich?

As I recall, the original question was when you were at fast idle.
Mike pointed out that you shouldn't even try to get to stoich at RPMs
that low. Tune it where your engine is happy. Stoich is highly
overrated as a point to tune your engine to.

b> Do I go rich and inch it down until it swings or go weak and inch
b> it up until it swings? Somewhere in the middle? Another way?

If you are talking about tuning at any RPM with a NBO2 sensor (such as
cruise where it makes a little more sense) then there are 2 answers.
1)Use MSTweak3000 because it is written to note the pulsewidth when
the flip occurs and back calculate to the necessary VE for the bin the
engine is operating in. 2)If you are tuning manually, don't even try
to do this, as a human you are simply not good enough.

b> Interesting that MSTweak uses this swinging band but where does
b> it decide the best point to adjust to?

I jumped the gun because I was reading as I replied, answer above...

b> Can you see what I mean or am I asking stoopid stuff?

Not stupid, just uninformed. But we will fix that.

b> At the moment my car idles OK but drives like sh*t!

That is why you don't want to tune to stoich. Tune it by ear to where
your engine feels happy and then you can say it runs great.

--
Later, http://thegebharts.com
Colin. mailto:colin@thegebharts.com

My wicked email client is http://www.ritlabs.com/the_bat/index.html
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knowledge. -unattributed



(posted by email)

Thanks all,

Lance, I had read read that in the FAQ/pdf manuals but its good to be told its the way to do it.

Colin, good info and advice.

I'll get her on the road and play around with the VE to get it near enough then start logging.

Will let y'all know how I get on.

Bob