...who has the best way to describe the differences. I'm trying to explain it to someone...and they still don't get it. Does anyone have a list of sensors that are ignored in open loop?

 

On the 86, the system only uses the TPS and the Coolant Temperature sensors in Open Loop. From their input, the ECM uses pre-programmed maps burned into the Programmable Read-Only Memory (PROM) to set timing and fuel. The PROM or "chip" is plugged into the car's computer, or ECM. Changing these maps can be done by re-programming the PROM using special equipment.

Our system has several different, what are referred to as Modes. Open Loop and Closed Loop are just two of the several different Modes the system can be in. Depending on which Mode the system is in, the ECM goes to certain maps or tables to grab the data it needs to adjust the fuel and timing the engine sees.

Once the other sensors meet certain parameters, (like temperature, time, cycling, etc.) which are also burned in the PROM, the system switches to Close Loop. During Closed Loop the sensors provide input to the ECM. For example, in Closed Loop, the 02 sensor provides feedback to the ECM as to the oxygen content in the exhaust gasses. Based on that input the fuel flow and timing are altered. The ECM alters the signals sent to the injectors to increase or decrease their "On" time, which is measured in milliseconds. More or less timing is also used based on sensor input. During Closed Loop,the input from other sensors, like the Mass Air Flow Sensor (MAF) is also used by the ECM to determine the correct timing and air fuel (A/F) ratio.

In Closed Loop, the system continually tries to maintain an A/F ratio of 14.7:1 which is 14.7 parts of air for every one part of fuel. However, our systems are not capable of maintaining a steady 14.7:1 A/F ratio, so the system constantly cycles between rich and lean using what you might call the "averaging method" to keep the A/F as close to 14.7:1 as it can. Sometimes the A/F ratio will be leaner than that, other times richer.

So, the ECM is constantly monitoring and altering the fuel and timing based on what the sensors tell it.

As the engine's operating conditions change, (coolant temperature rises, engine RPMs increase/decrease, throttle position changes, etc.) the ECM continually adjusts the timing and fuel, always striving for that magical 14.7:1. Some of these changes (referred to as Block Learn Memory or BLM) can be relatively major. Others (referred to as Intergrator values) are more like fine-tuning. 14.7:1, BTW, was determined to be the best compromise between low emissions and fuel economy. It's not the best ratio for maximum power, just the best for part throttle performance, all things considered.

There'll be others who will nit-pick this explanantion (we never seem to run out of nit-pickers - I believe it's an ego thing going on), but, anyway, that's generally how it works.

Jake

 

Very well written explaination.

 

Good explaination. Now you did remember to wear your flame proof undergarments?

 

LOL

I generally try to ignore the comments of those who have a history of nit-picking. Something in their personality forces 'em to do it.

After being on the Forum for several years, I pretty much know what to expect from those few; they never change.

Confrontation, I figure, isn't worth the effort.

Jake

 

You got that right!

 

great explanation...thank you.