QWKSNKE
08-04-2005, 04:39 PM
Quoted from Bob (boss96) who quoted Clint on the Tweecer forums.
Many thanks to 86GT for posting this info! It's a little long...I was having problems with my idle quality, until I read all of the post on the EEC Tuner and Tweecer forums. I would like to give credit where credit is due, but I read so many different posts that the list would go on forever. So basically, I would like to give credit to all members of the forums that have posted any thing about idle quality. What I have done here is consolidate the efforts of many individuals and threw in my two cents along the way. This procedure is written around an A9L processor.
· Adjust the idle screw on the Throttle Body (TB) all the way out allowing the throttle plate to fully close. Now turn the idle screw in just until it touches the mechanical linkage. Finally, turn the idle screw in one full turn. This will place the TB plate at the correct location.
· Adjust the Throttle Position Sensor (TPS) to .98Vdc using CalCon. You may have to ream out the mounting slots on the TPS in order to achieve .98Vdc. There has been a lot of discussion about what the correct TPS setting should be, but I have found that .98Vdc works fine for me. Note: the voltage reading at the sensor may be different from CalCon’s reading due to line resistance. If the TPS wiring is in good shape, then the voltage difference should be minimal. If there is a significant difference find the bad connector or wiring and fix it before continuing.
· Unplug the Idle Speed Controller (ISC) so that you can datalog the base idle. Now start the car and datalog the idle RPM and Mass Air Flow (MAF) voltage at normal operating temperatures. After achieving the datalog, calculate an average MAF voltage vrs RPM. For example:
MAF RPM
.8 675
Plug the ISC back in.
· Now its time to start entering parameters into CalEdit, but first let me describe how the functions and scalars work that pertain to the ISC. The scalar “Throttle Body Air†is used to tell the EEC how much air in pounds per minute enters the engine through the TB at an idle. The factory uses a 60mm TB and a 55mm MAF with a base idle of 550. The stock combination will produce a MAF voltage of .615 Vdc at 550 RPM. Using the formula (MAF * 2.2046226 / 60 = TB Air Flow) you will see how the factory came up with the numbers they did. For example ( [.615Vdc = 14.969kg/hr] *2.2046226 / 60 = .55005 pounds/minute) will result in the factory setting of .55005. With that in mind, I’m using a 70mm BBK TB and a 73mm C&L meter with a 93 Cobra intake, which produces a MAF voltage of .8 at 650 RPM. Using the formula above and the MAF curve I calculated the new TB airflow. Keep in mind the MAF curve needs to be tuned properly, or this calculation will be wrong. My new TB airflow is ([.8Vdc = 25.357kg/hr] * 2.2046226 /60 = .93). Also keep in mind that every time you adjust the idle that the TB airflow needs to be recalculated.
· Now the function “ISC Neutral Idle Air Flow†can be adjust to accommodate the new TB airflow. The factory uses .75 air for 672 RPM, thus by subtracting the TB Air Flow you get .2 air at 672 RPM. Here is where I believe people get confused. I have read in many of the forums that the ISC should be about 20 % duty cycle at an idle, but I believe this to be miss leading. If the stock application has .2 air at an idle, as proven above, then by looking at the function “ISC Transfer†you will see that .2 air dictates that .34 or 34% duty cycle is applied. Maybe I’m wrong, but if you now adjust the idle up a little by using the TB set screw then the ISC duty cycle will go down in order to maintain the desired RPM. This is how I believe the 20% duty cycle is possible. The factory Idle is set to 672 with a base of 550, which is a difference of 122 RPM. This difference is what allows the ISC duty cycle to be at 34%. So if you take the desired RPM and lower it, you should see that the duty cycle should also decrease and vise versa. For my set up I entered values into the function “ISC Neutral Idle Air Flow†that corresponded to my new MAF curve.
· The purpose of the function “ISC Dashpot Pre Position†is to tell the EEC where to maintain the idle during release of the throttle. In my case the desired RPM is 750, which tells me that the preposition of the ISC is .36 air or .42 duty cycle. In my case this held my RPM’s at 1000. The time that the RPM’s are held is dependent on a couple of thing, one the Vehicle Speed Sensor (VSS) and some constant, which I cannot find. As long as the vehicle is moving above (7 MPH I think) the Dashpot Preposition is active. Once the vehicle drops below 7MPH then the RPM’s will drop to the desired RPM. If the car is at a stop and the engine is reved then I believe some time constant is used for the Dashpot Pre Position. On my set up, the RPM’s will drop to 1000 and hold there for about 2 seconds. I can’t seem to find this setting anywhere.
· The purpose of the function “ISC Decay Rate†is to tell the EEC how fast to drop the RPM’s to the Dashpot Pre Position. I believe the units are in seconds. This means that the stock application will drop the RPM’s over 750ms or ¾ of a second. For my set up, I did not have to touch this function.
I found another discovery that may help people. I had a stable idle with the procedure above, but my timing was swinging all over the place. It was swinging from 15 to 31 degrees. After looking at the "Idle Spark vs. RPM" function, this is what it is suppose to do if the RPM error exceeds 175. This meant that the "ISC Neutral Idle Air Flow" was not set correctly. I verified this by zeroing out the "ISC Neutral Idle Air Flow" function and watching the idle. It was about 200 RPM's below desired. This explained the timing adder. WOW, I'm finally starting to get a hold on this idle thing.
I also had a Ford mechanic (mustang guru like us) look at it, and he told me that Ford had issued a Tech Bulletin that stated the idle should be set by monitoring the timing if any after market air componets have been installed. They are suppose to adjust the Idle set screw in (higher RPM) until they achieve a time of around 12 degrees, but they are not to exceed 750 on the idle. He said this was to get rid of the RPM error. He also stated that the EEC was designed to control the idle with the ISC and that the timing is supposed to be used as a secondary idle control. Ford states this is a common problem with larger TB and air meters.
With that in mind, I created an excel sheet that calculates a new TB airflow scalar and the "ISC Neutral Idle Air Flow" function. These calculations are based off of a good known MAF transfer function and a datalog with the ISC disconnected. The datalog must contain an RPM range up to 2000. If anyone is interested, I will send it to you via E-mail.
I now have a rock solid idle. WOW
Many thanks to 86GT for posting this info! It's a little long...I was having problems with my idle quality, until I read all of the post on the EEC Tuner and Tweecer forums. I would like to give credit where credit is due, but I read so many different posts that the list would go on forever. So basically, I would like to give credit to all members of the forums that have posted any thing about idle quality. What I have done here is consolidate the efforts of many individuals and threw in my two cents along the way. This procedure is written around an A9L processor.
· Adjust the idle screw on the Throttle Body (TB) all the way out allowing the throttle plate to fully close. Now turn the idle screw in just until it touches the mechanical linkage. Finally, turn the idle screw in one full turn. This will place the TB plate at the correct location.
· Adjust the Throttle Position Sensor (TPS) to .98Vdc using CalCon. You may have to ream out the mounting slots on the TPS in order to achieve .98Vdc. There has been a lot of discussion about what the correct TPS setting should be, but I have found that .98Vdc works fine for me. Note: the voltage reading at the sensor may be different from CalCon’s reading due to line resistance. If the TPS wiring is in good shape, then the voltage difference should be minimal. If there is a significant difference find the bad connector or wiring and fix it before continuing.
· Unplug the Idle Speed Controller (ISC) so that you can datalog the base idle. Now start the car and datalog the idle RPM and Mass Air Flow (MAF) voltage at normal operating temperatures. After achieving the datalog, calculate an average MAF voltage vrs RPM. For example:
MAF RPM
.8 675
Plug the ISC back in.
· Now its time to start entering parameters into CalEdit, but first let me describe how the functions and scalars work that pertain to the ISC. The scalar “Throttle Body Air†is used to tell the EEC how much air in pounds per minute enters the engine through the TB at an idle. The factory uses a 60mm TB and a 55mm MAF with a base idle of 550. The stock combination will produce a MAF voltage of .615 Vdc at 550 RPM. Using the formula (MAF * 2.2046226 / 60 = TB Air Flow) you will see how the factory came up with the numbers they did. For example ( [.615Vdc = 14.969kg/hr] *2.2046226 / 60 = .55005 pounds/minute) will result in the factory setting of .55005. With that in mind, I’m using a 70mm BBK TB and a 73mm C&L meter with a 93 Cobra intake, which produces a MAF voltage of .8 at 650 RPM. Using the formula above and the MAF curve I calculated the new TB airflow. Keep in mind the MAF curve needs to be tuned properly, or this calculation will be wrong. My new TB airflow is ([.8Vdc = 25.357kg/hr] * 2.2046226 /60 = .93). Also keep in mind that every time you adjust the idle that the TB airflow needs to be recalculated.
· Now the function “ISC Neutral Idle Air Flow†can be adjust to accommodate the new TB airflow. The factory uses .75 air for 672 RPM, thus by subtracting the TB Air Flow you get .2 air at 672 RPM. Here is where I believe people get confused. I have read in many of the forums that the ISC should be about 20 % duty cycle at an idle, but I believe this to be miss leading. If the stock application has .2 air at an idle, as proven above, then by looking at the function “ISC Transfer†you will see that .2 air dictates that .34 or 34% duty cycle is applied. Maybe I’m wrong, but if you now adjust the idle up a little by using the TB set screw then the ISC duty cycle will go down in order to maintain the desired RPM. This is how I believe the 20% duty cycle is possible. The factory Idle is set to 672 with a base of 550, which is a difference of 122 RPM. This difference is what allows the ISC duty cycle to be at 34%. So if you take the desired RPM and lower it, you should see that the duty cycle should also decrease and vise versa. For my set up I entered values into the function “ISC Neutral Idle Air Flow†that corresponded to my new MAF curve.
· The purpose of the function “ISC Dashpot Pre Position†is to tell the EEC where to maintain the idle during release of the throttle. In my case the desired RPM is 750, which tells me that the preposition of the ISC is .36 air or .42 duty cycle. In my case this held my RPM’s at 1000. The time that the RPM’s are held is dependent on a couple of thing, one the Vehicle Speed Sensor (VSS) and some constant, which I cannot find. As long as the vehicle is moving above (7 MPH I think) the Dashpot Preposition is active. Once the vehicle drops below 7MPH then the RPM’s will drop to the desired RPM. If the car is at a stop and the engine is reved then I believe some time constant is used for the Dashpot Pre Position. On my set up, the RPM’s will drop to 1000 and hold there for about 2 seconds. I can’t seem to find this setting anywhere.
· The purpose of the function “ISC Decay Rate†is to tell the EEC how fast to drop the RPM’s to the Dashpot Pre Position. I believe the units are in seconds. This means that the stock application will drop the RPM’s over 750ms or ¾ of a second. For my set up, I did not have to touch this function.
I found another discovery that may help people. I had a stable idle with the procedure above, but my timing was swinging all over the place. It was swinging from 15 to 31 degrees. After looking at the "Idle Spark vs. RPM" function, this is what it is suppose to do if the RPM error exceeds 175. This meant that the "ISC Neutral Idle Air Flow" was not set correctly. I verified this by zeroing out the "ISC Neutral Idle Air Flow" function and watching the idle. It was about 200 RPM's below desired. This explained the timing adder. WOW, I'm finally starting to get a hold on this idle thing.
I also had a Ford mechanic (mustang guru like us) look at it, and he told me that Ford had issued a Tech Bulletin that stated the idle should be set by monitoring the timing if any after market air componets have been installed. They are suppose to adjust the Idle set screw in (higher RPM) until they achieve a time of around 12 degrees, but they are not to exceed 750 on the idle. He said this was to get rid of the RPM error. He also stated that the EEC was designed to control the idle with the ISC and that the timing is supposed to be used as a secondary idle control. Ford states this is a common problem with larger TB and air meters.
With that in mind, I created an excel sheet that calculates a new TB airflow scalar and the "ISC Neutral Idle Air Flow" function. These calculations are based off of a good known MAF transfer function and a datalog with the ISC disconnected. The datalog must contain an RPM range up to 2000. If anyone is interested, I will send it to you via E-mail.
I now have a rock solid idle. WOW