Just curious, but why would you want to?

 

If you're just cruising around, the stock A/F ratio setting offers a nice medium between performance and economy. It's the WOT A/F ratio that you want to pay attention to.

 

Bingo! LOL

I guess there might be a reason to change it on a really odd or big buildup but I can't think of any. Thats why I was curious.

 

14.8 is not a power orientated a/f mixture. It is an emmissions orientated a/f ratio.

Changing this value rather than the MAF table to obtain a richer a/f ratio would be a much "cleaner" edit to the PCM, and would have more predictable outcomes if it does indeed change the target a/f ratio of the engine.

Sooooo, has anybody done this. Does it change the target a/f ratio of the PCM???

 

Exactly. You're not trying to make power at idle or running down the highway at 70. All you're going to get out of this is shitty gas mileage in my opinion.

 

Guys,

I think that if you change this value then you are changing the value that the o2 sensors are trying to obtain, correct?

Our o2s are very accurate around 14.7:1 when you start to play with this number you are going to move them away from where they are their most accurate.

I would say leave this alone.

Scott

 

You're right Scott, and that's probably the most important reason to leave it alone.

 

I have heard that the oxygenated gas that comes from the pumps in the winter time will work better with a ratio of about 14.2 to one. The theory sounds right since there is more oxygen in the liquid fuel, but I have not had any experience trying this. Just passing on some info I have heard.

 

But the sensors ability to gauge a/f is still changed from where it is most accurate...that is where the problems come in.

Does anyone know the range the factory o2 sensors can read with accuracy? I know that my wideband will go from 10:1 to 20:1.

Scott

<small>[ August 01, 2002, 06:43 PM: Message edited by: Scott 98Z M6 ]</small>

 

Once you change the goal of the O2 sensors at idle and part throttle, you are going to have to edit every fuel managent table. Your PE vs RPM, PE vs Temp, MAF, etc. Nothing is going to be correct. <img border="0" alt="[Banging Head]" title="" src="graemlins/gr_banghead.gif" />

It is a waste of time trying to correct something that is already correct for the purpose it serves. As stated before, you should be concentrating on your WOT tuning. Get your closed loop ltrims to between 0 and -2%, then work on your WOT.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by DenzSS:
[QB]Once you change the goal of the O2 sensors at idle and part throttle, you are going to have to edit every fuel managent table. Your PE vs RPM, PE vs Temp, MAF, etc. Nothing is going to be correct. <img border="0" alt="[Banging Head]" title="" src="graemlins/gr_banghead.gif" />
QB]</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I respectfully disagree.

Table corrections are factored in as a percentage correction to obtain the desired a/f ratio. The table values do not determine the a/f ratio.

By changing the target a/f ratio (ie the desired O2 voltage reading) your Lterms will direct the engine accordingly to reach this reading.

This would be the ideal correction for people, like me, who's car is not running at the desired a/f ratio even when there is .9 volts on both O2's.

When my PCM finally (takes about 2000 miles) gets the car adjusted to .9 volts on the O2's (0 Lterms at part throttle) THE CAR IS STILL LEAN. So, in reality, my car is not running with a 14.8 a/f ratio, but more like a 15.3 (or something like that) EVEN THOUGH THE PCM THINKS IT IS 14.8.

Changing the desired a/f ratio from 14.8 to, oh lets say, 14.4 would dial in my car to the CORRECT a/f ratio of 14.8

That is why I am asking this; to adjust a car to the correct a/f ratio when it can't get there on its own.

So, can I adjust this stoich ratio to something (for example) like 14.4 or 14.0. How low can I go? How high can I go? If I adjust it, will the car spontaneously explode?

 

HOW DO THOSE BOXES WORK THAT PLUG INTO YOUR MAF. ARE THOSE ACCURATE? DO THEY HELP? ARE THEY WORTH 179 BUCKS?

 

Those O2 sensors also measure ambient air temp, and the amount of oxygen in your exhaust. I wouldn't go any lower than 14.0 and no higher than 14.8. It would seem to me that you would have to redo your maps.The oxygen sensor or the lambda sensor's signal is monitored by the control unit, which then adjusts injector pulse time to maintain the programmed 14.7:1 ratio.The sensor only creates voltage if the outside ambient air is higher in oxygen content than the exhaust. The voltage will put out little or no voltage if you're lean and higher voltage in a rich condition. If you run rich with these Bosch systems, your exhaust temp will rise and you can overheat or even melt your catalytic converters. I have found that you just don't benefit by running any richer than 14.0:1. The old carburetors were usually running rich at anywhere from 12.5:1 to 13.5:1.

 

Understood.

What are your mods? Do you have a really radical fuel system?

 

There is no reason to adjust the stoich a/f ratio. This value in the PCM is a reflection of the physical properties of the sensor itself.

If you want to change your a/f ratio at part throttle you need to switch to open loop mode and use the AFR for open loop table.

If you wish to use O2 sensor feedback you are stuck with what the sensor itself is designed for. Using other values will not give predicatable or repeatable results since you will be outside the range the o2 sensor was desinged to work in.

Chris

 

Engine ---> Fuel ---> Stoich Ratio

Stock this value is 14.736 (~14.8) if I want to change my cars desired A/F ratio, can I just change this value.

I realize that the Edit book says only change this if you change your O2 sensors....why?

Has anybody changed this value??

What results did it have??

Thanks for the input <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

I would like to know this as well. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

 

Thanks for the replies guys. I was looking for an easy solution, but it looks like that isn't it..... back to the tables, *sigh*.

The car is an ARE Stg II H/C with some other goodies. Unfortunately, it just loves to run lean.

Thanks Again for the help

<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

It may be the damn cam. It sounds to me like you may need to work on adjusting the optimum duration on the exhaust side, because that would affect your exahust side. That's what the 02 sensor is adjusting for. It may have too much duration, causing a rich condition, and the sensor are picking up on that. Then the computer is overly adjusting the your mixture to meet emisions based on the stock fuel map, causing the lean condition.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by ChrisB:
<strong>
If you wish to use O2 sensor feedback you are stuck with what the sensor itself is designed for. Using other values will not give predicatable or repeatable results since you will be outside the range the o2 sensor was desinged to work in.
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">The question is can you get to run slightly out side that value for emission testings and put it back after the test?