How does a chip maintain a different A/F than the stock stoichiometric ratio of 14.7?

[Slider]

The title basically says it all. From what I know the oxygen sensors are only good at measuring the a/f as either Lean or Rich. For a stock car the PCM tries to alternate evenly between these two so that on average the a/f is at the stoichiometric ratio of 14.7. That is if the car is rich it leans it out, and vise versa. When you have a chip programmed for your car one often needs an a/f of other than 14.7. How the heck does that work since the PCM cannot measure it?

If you alter the fuel tables so that you have the a/f set rich with a wideband O2 in the exhaust, then how do you keep the PCM from forcing it back to 14.7.

Maybe I do not fully understand the closed and open loop operation of the PCM, but I thought that it would try to force the a/f back it it is wrong. It would alter several parameters in clsoed loop so that it was 14.1. The amount the closed loop parameters were altered is then used to adjust the open loop parameters, there by messing up your tune.

Is there some settings that are changed using the chip that do not allow the PCM to adjust the values in closed loop, or it is set so the closed loop values cannot adjust the open loop parameters?

 

[DBMSTNG]

a chip overrides the PCM perameters and sets hard values instead of the variable values. so as is the case with timing, the pcm can alter timing based on air temp. a chip has a constant degree of timing that does not change for different air temps.

 

[Bullit#3441]

Ball bearings. It's all about ball bearings these days.

 

[billyfe390]

14.7 will be the a/f at idle after that .......well screw it here is the full version.

http://www.mustangworks.com/articles/electronics/InductionBlues.html
and here
http://www.mustangworks.com/articles/electronics/eecAdaptive.html

It is directed towards eecIV but eecv works pretty close to the same way.

Basically with a chip you are telling the ecm what to do at a certain rpm. The chip actually overrides the processor and all of the maps are run from the chip instead of the ecm. When you tune you set your maps for open loop and basically tell the car what a/f to run at a certain rpm. Read through some of the stuff about eeciv that mike wesley wrote in www.mustangworks.com that is probably the best explaination you will find about how the computer figures how much fuel it needs to run.

If you are running 14.7 at anything other than idle you are asking for trouble that is way way too lean and unless there is something wrong.

 

[Slider]

Ball Bearings

Thanks for the links. I will look through them, and come back with more questions

 

[Slider]

I read thos earticle, and it did not help.

Ok, I can see maybe a chip intercetping the data and changing it to fool the PCM.

Maybe I should of been more clear, but what about having your PCM relfashed or reprogrammed using something like th SCT software. Are they completely disabling the closed loop operation and you run on open loop all the time?

 

[billyfe390]

I read thos earticle, and it did not help.

Ok, I can see maybe a chip intercetping the data and changing it to fool the PCM.

Maybe I should of been more clear, but what about having your PCM relfashed or reprogrammed using something like th SCT software. Are they completely disabling the closed loop operation and you run on open loop all the time?

No all you do with a reflash is just remap the open loop tables according to what your needs are. I could be wrong but I highly doubt you mess with any of the closed loop stuff.

 

[Eminent18]

with a chip you can set certain rpms to reach a certain a/f ratio.

 

[Slider]

with a chip you can set certain rpms to reach a certain a/f ratio.

Yeah, but you cannot measure an a/f other then rich or lean about 14.7. The oxygen sensor is not that precise. Fine if it could measure the exact a/f, but it cannot. If you cannot measure the a/f other then rich or lean about 14.7 how do you get the computer to do some other a/f. The closed loop control of the computer tries to maintian this condition and there is no other a/f tht it can do because of teh O2 sensor. Aslo, from what I know the adaptive info from the closed loop control is feed to the open loop control so that if you change the open loop parameters the feedback control changes them again. This is the basic reason that things like adjustable pressure regulators do not work properly in the long run. The feedback control of the computer eventual shortens the fuel injector pulse width so that even with the higher fuel pressure you still get 14.7. This closed loop data is then used to alter the open loop data (over time) so even at WOT you have not richened the mixture.

 

[billyfe390]

You never never at WOT or anything other than idle have an A/F ratio at 14.7 period unless there is something drasticaly wrong or you have some mismatched un-calibrated aftermarket parts.

The O2 sensors are not the only sensor that the ecm uses to determine A/F. A combination of MAF voltage, TPS voltage, Intake air temp, engine temp and timing all get combined to determine the proper A/F ratio. I am sure I left some out but you get the idea.

 

[Slider]

But the O2 sensor is the only thing that is really used in closed loop to determine the main a/f. If it was not that important why would it be used at all.

Maybe you need to look over those links you posted. Here is a paragraph from the one link that really points out how the closed loop works with the O2 sensor.

From this example, you'll quickly see why an adjustable pressure regulator might not be a good investment of your money. Ford uses a fuel pressure of roughly 39 PSI to rate it's fuel injectors. The fuel regulator operates in conjunction with manifold pressure to keep the delta pressure across the fuel injectors at roughly 39 PSI at all times. In the EEC calibration, there is a number that represents the size of the injectors installed in the engine. This number represents how much fuel the injector will flow at 39 PSI. The EEC uses this number, along with airflow information to correctly calculate A/F ratio. Based on the airflow number and it's target A/F ratio, the EEC pulses the fuel injector to give just the right amount of fuel to reach it's target A/F ratio at any given Speed/Load point. Now if you were to increase the fuel pressure, the amount of fuel delivered for a given pulsewidth would go up since more fuel will be forced through the injector. As soon as the EEC goes into Closed Loop control, it will 'see' this increased fuel pressure. The reason for this is for any given pulsewidth, the A/F ratio as measured by the oxygen sensor will be richer than what the EEC wanted it to be since now there is more fuel delivered with the same pulsewidth. The EEC will calculate the difference from what it wanted and what it got and update the Adaptive table with a 'correction factor' and use this correction factor to reduce the injector pulsewidth the next time the injector fires. Eventually what happens is the EEC is able to 'dial out' the extra fuel that was added by increasing the fuel pressure. Now you can probably see why raising the fuel pressure is only a temporary 'fix' for a lean problem. Soon you will be right back where you started from. The EEC is continuously updating the Adaptive table anytime it is in Closed Loop.

Here is some info quoted about the open loop.

"What about Open Loop?" you might ask. Well, it works there too. This fact alone is know by very few people. Most people think Adaptive only works when in Closed Loop. This is wrong! Adaptive is only UPDATED during Closed Loop. It would be silly to ignore changes in the air and fuel system in Open Loop and only correct them in Closed Loop. If you have a serious fuel problem, your car might not even start if the EEC didn't have some way of correcting things all the time. The way the EEC uses Adaptive in Open Loop is similar to Closed Loop except it doesn't update the table. This means it's not looking at the oxygen sensor for feedback. It is merely relying on the information stored in the table to make corrections. Since the Adaptive table only contains Speed / Load points normally seen during Closed Loop, where does the correction factor come from if I'm at WOT? Good question. The answer is; it uses the last value it was using while in Closed Loop.

 

[jstreet0204]

Yeah, but you cannot measure an a/f other then rich or lean about 14.7. The oxygen sensor is not that precise. Fine if it could measure the exact a/f, but it cannot. If you cannot measure the a/f other then rich or lean about 14.7 how do you get the computer to do some other a/f. The closed loop control of the computer tries to maintian this condition and there is no other a/f tht it can do because of teh O2 sensor. Aslo, from what I know the adaptive info from the closed loop control is feed to the open loop control so that if you change the open loop parameters the feedback control changes them again. This is the basic reason that things like adjustable pressure regulators do not work properly in the long run. The feedback control of the computer eventual shortens the fuel injector pulse width so that even with the higher fuel pressure you still get 14.7. This closed loop data is then used to alter the open loop data (over time) so even at WOT you have not richened the mixture.

Once the eec goes into open loop it no longer is trying to maintain a particular a/f ratio. it uses tables and functions to put X amount of fuel into the engine when Y amount of incoming air and Z amount of RPM exists. The adaptive table can only adjust X a very small amount based on the last value it had in closed loop. This is the extremely simpified version. There is probably a dozen ways to tune the a/f the easiest being the WOT fuel multiplier.

 

[billyfe390]

Yes it is the only thing used for the INITIAL ratio I never said it wasnt. What I was saying is it is not the only reading that the computer uses to determine what the end A/F at a given rpm is. It is just the first reading it sees then it uses other multipliers and tables to adjust to what it thinks is best for the motor.

 

[allutz]

Ball bearings. It's all about ball bearings these days.

great movie !!!!! gotta clean up this muck.....

 

[allutz]

the o2 sensors do one thing and one thing only.......they measure oxygen in the exhaust stream.....thats it!! from there the pcm figures what is needed and when given the other variables its reading with other sensors(laymans terms)

 

[Slider]

So, basically what you are saying is that when you have your PCM reflashed/programmed they minimize the effect of the O2 sensor by emphasizing the other variables (or de-emphasizing the O2 if you want to look at it that way) that also help the PCM determine a/f. So that way the O2 sensor is still in the loop, but its impact is not as important. I would assume that you also minimize the impact of the closed loop parameters on the open loop ones.

Does that sound more like it? Not trying to be a pain. I am just trying to get a good grasp on this stuff.

 

[billyfe390]

So, basically what you are saying is that when you have your PCM reflashed/programmed they minimize the effect of the O2 sensor by emphasizing the other variables (or de-emphasizing the O2 if you want to look at it that way) that also help the PCM determine a/f. So that way the O2 sensor is still in the loop, but its impact is not as important. I would assume that you also minimize the impact of the closed loop parameters on the open loop ones.

Does that sound more like it? Not trying to be a pain. I am just trying to get a good grasp on this stuff.

Yes and No

There are 4 spark tables and several fuel tables that all get altered during tuning. I am not a tuner but I did spend a week with my tuner working out the diablo software that he just bought. I do know all of the small adjustments are based off of a whole slew of other sensor readings so everything needs to be working within specs in order to calibrate the Maf and get what you want.

Your best bet for your answer go to a tuner and either watch him tune something or have him show you the tables because it is far too complicated to explain in here.

 

[Slider]

Yes and No

There are 4 spark tables and several fuel tables that all get altered during tuning. I am not a tuner but I did spend a week with my tuner working out the diablo software that he just bought. I do know all of the small adjustments are based off of a whole slew of other sensor readings so everything needs to be working within specs in order to calibrate the Maf and get what you want.

Your best bet for your answer go to a tuner and either watch him tune something or have him show you the tables because it is far too complicated to explain in here.

Thanks for your input. It has been very helpful

I will have to just keep looking for info and bugging people until I feel like I undnerstand it.

 

[KenB]

Thanks for your input. It has been very helpful

I will have to just keep looking for info and bugging people until I feel like I undnerstand it.

Didn't I already explain this to you? If you didn't get it, tell me why and I'll try and do a better job. It's really not that complicated.

Ken

 

[KenB]

So, basically what you are saying is that when you have your PCM reflashed/programmed they minimize the effect of the O2 sensor by emphasizing the other variables (or de-emphasizing the O2 if you want to look at it that way) that also help the PCM determine a/f. So that way the O2 sensor is still in the loop, but its impact is not as important. I would assume that you also minimize the impact of the closed loop parameters on the open loop ones.

Does that sound more like it? Not trying to be a pain. I am just trying to get a good grasp on this stuff.

I'll try and explain it a little better

There are two 'modes' you can be in, open loop and closed loop.

Closed Loop
The EEC uses the front O2 sensors as feedback to maintain 14.64:1 Air Fuel Ratio. This is generally at idle/part throttle situations.

Open Loop
The EEC doesn't use the O2's in this mode. It uses the MAF. The EEC knows the displacement of the engine (how much air it's capable of sucking in) and via the MAF, it knows how much air it actually is sucking in. This ratio is called load. At WOT load reaches close to 100%. If the EEC knows how much air the engine is getting and it knows what size injectors are in the car, it can command a specific A/F ratio by adding/subtracting fuel based on the amount of air.

This is how the car works stock, no tuning.

With a tune, none of this changes. Depending on year, a stock 99+ stang commands 12:1 A/F. So all you need to do is change that value to whatever you wish. It's very simple.


Now some of the problems you run into is when people change MAFs. The MAF is a meter that measures the Mass of the air and sends this as voltage to the EEC. The EEC has a Mass Air Transfer function. Based on the voltage the EEC sees, it knows how much air it is getting. With a stock MAF, this function is very accurate. Once you change the MAF, this function is wrong. That's where a really good tuner shines through. If you adjust the MAF transfer function to work correctly after a MAF change, you can still command a specific A/F ratio and it will work.

If you change MAFs and don't adjust the transfer function, then things will be off and will have to start fudging the fuel tables and things start to go down hill. This is one of the things that seperate a good tuner from a bad tuner.

Obviously there are alot more factors and it's gets more complicated, but hopefully this explains it better.

Ken