Rbob, a question for you
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Rbob, a question for you
While searching for some more info about tables affecting O/L fueling, I ran across the following you posted saometime back.
Please tell me if I am figuring this correctly. From what I have read, the ECM will not control the idle speed (in C/L) unless the steps between each IAC vs temp value is 24 (with the IAC kickdown set at 25). In other words, if I want my ECM to start controling the idle at 56c, I need the IAC counts (IAC vs Coolant) to be no less than 24 for each setting from 56c to hot?
TIA!
Well, I finally figured it out! It started with a new 195f thermostat that ended up being bad. Engine wouldn't get over 158f (70c) in coolant temp. So I have 20 minutes worth of low temp data.
The kicker was that the idle would not drop below ~1100 rpm. This was even with the idle vs coolant at 838 rpm. Hmmm, I've seen this before and now it's about time I looked into it.
The bottom line is that the kick down steps (@ $5D8) must be one step greater then the IAC position vs coolant table (@ $5F5) steps for the ECM to fully control the idle speed. To better understand, here is a cut of the IAC position vs coolant table (edit: from the hac, not the one I used):
Code:
*==============================================
* IAC MOTOR POSIT vs COOLANT
* (IN STEPS) ASDZ, 5.7L V8 TYPE $42 ECM
*
*
* TBL = STEPS
*==============================================
ORG $05F5 ;
; STEPS ; Deg c Deg f
;---------------------------------
LD5F5 FCB 24 ; HOT HOT
LD5F6 FCB 24 ; 136.0 277
LD5F7 FCB 24 ; 107.0 225
LD5F8 FCB 24 ; 91.0 196
LD5F9 FCB 24 ; 80.0 176
LD5FA FCB 24 ; 71.0 160
LD5FB FCB 24 ; 63.0 145
LD5FC FCB 24 ; 56.0 133
LD5FD FCB 40 ; 49.3 121
LD5FE FCB 50 ; 43.3 110
LD5FF FCB 65 ; 37.0 99
LD600 FCB 80 ; 30.5 87
LD601 FCB 90 ; 23.5 74
LD602 FCB 100 ; 15.5 60
LD603 FCB 110 ; 6.0 43
LD604 FCB 120 ; -8.5 17
LD605 FCB 145 ; COLD COLD
*==============================================
Note the steps of 24 between HOT and 56c/133f. These values are one less than the kick down steps @ $5d8. It is set to 25.
What this means is that the ECM will take full control of the idle only when the coolant reaches 56c/133f. Then and only then will the ECM attempt to control the high idle rpm. (Now, kick down also has to have occurred. This is at $5d7, in seconds after eng start. Usually not a great period of time). This is when the ECM finally uses the IAC desired idle vs. coolant table at $60E.
Once the coolant is above the temp at $5F3 there is a high limit. The idle speed will be reduced if too high. This upper limit is at $5E1, in rpm / 12.5. Below that temp there is no upper rpm limit.
Until the coolant reaches the value that the IAC position vs coolant steps are less than the kick down steps, the ECM will only reduce the idle speed when it's above the upper limit.
So if you have changed the kick down steps or the IAC position vs. coolant table, make sure the table shown above has the proper steps: one less than the kick down steps, at the coolant values desired. If not the idle will tend to 'hang' high. Also note the upper idle limit at $5E1 that is used until the cutover to full idle speed control.
The kicker was that the idle would not drop below ~1100 rpm. This was even with the idle vs coolant at 838 rpm. Hmmm, I've seen this before and now it's about time I looked into it.
The bottom line is that the kick down steps (@ $5D8) must be one step greater then the IAC position vs coolant table (@ $5F5) steps for the ECM to fully control the idle speed. To better understand, here is a cut of the IAC position vs coolant table (edit: from the hac, not the one I used):
Code:
*==============================================
* IAC MOTOR POSIT vs COOLANT
* (IN STEPS) ASDZ, 5.7L V8 TYPE $42 ECM
*
*
* TBL = STEPS
*==============================================
ORG $05F5 ;
; STEPS ; Deg c Deg f
;---------------------------------
LD5F5 FCB 24 ; HOT HOT
LD5F6 FCB 24 ; 136.0 277
LD5F7 FCB 24 ; 107.0 225
LD5F8 FCB 24 ; 91.0 196
LD5F9 FCB 24 ; 80.0 176
LD5FA FCB 24 ; 71.0 160
LD5FB FCB 24 ; 63.0 145
LD5FC FCB 24 ; 56.0 133
LD5FD FCB 40 ; 49.3 121
LD5FE FCB 50 ; 43.3 110
LD5FF FCB 65 ; 37.0 99
LD600 FCB 80 ; 30.5 87
LD601 FCB 90 ; 23.5 74
LD602 FCB 100 ; 15.5 60
LD603 FCB 110 ; 6.0 43
LD604 FCB 120 ; -8.5 17
LD605 FCB 145 ; COLD COLD
*==============================================
Note the steps of 24 between HOT and 56c/133f. These values are one less than the kick down steps @ $5d8. It is set to 25.
What this means is that the ECM will take full control of the idle only when the coolant reaches 56c/133f. Then and only then will the ECM attempt to control the high idle rpm. (Now, kick down also has to have occurred. This is at $5d7, in seconds after eng start. Usually not a great period of time). This is when the ECM finally uses the IAC desired idle vs. coolant table at $60E.
Once the coolant is above the temp at $5F3 there is a high limit. The idle speed will be reduced if too high. This upper limit is at $5E1, in rpm / 12.5. Below that temp there is no upper rpm limit.
Until the coolant reaches the value that the IAC position vs coolant steps are less than the kick down steps, the ECM will only reduce the idle speed when it's above the upper limit.
So if you have changed the kick down steps or the IAC position vs. coolant table, make sure the table shown above has the proper steps: one less than the kick down steps, at the coolant values desired. If not the idle will tend to 'hang' high. Also note the upper idle limit at $5E1 that is used until the cutover to full idle speed control.
Please tell me if I am figuring this correctly. From what I have read, the ECM will not control the idle speed (in C/L) unless the steps between each IAC vs temp value is 24 (with the IAC kickdown set at 25). In other words, if I want my ECM to start controling the idle at 56c, I need the IAC counts (IAC vs Coolant) to be no less than 24 for each setting from 56c to hot?
TIA!
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From: Chasing Electrons
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There is a distinct and unconnected difference between closed loop fueling and closed loop idle control. They do not affect each other. Idle can go closed loop while fueling is open loop and vice-versa, etc.
In order to go closed loop idle the park/neutral input to the ECM must be in the 'Drive' position. While in park/neut there is no closed loop idle control.
BTW: we are talking about stock '7747 and '8746 code.
In order to go closed loop, besides the 'in drive' parameter, the kick down steps needs to be greater then the IAC vs. Coolant steps.
If the kickdown is 25 steps, and the coolant steps at 56C is 24, then at 56 C the ECM will go closed loop idle control. Same if the coolant steps at 56 deg are 10, the ECM will go closed loop shortly before reaching 56 C (interpolation between table entries puts the coolant steps at less then 25 before 56 C is reached).
OTOH: if the kick down steps are 15, and the lowest steps vs. coolant is 24, then closed loop idle will never happen.
Taking this statment of mine: The bottom line is that the kick down steps (@ $5D8) must be one step greater then the IAC position vs coolant table (@ $5F5) steps for the ECM to fully control the idle speed.
It should really read: "The bottom line is that the kick down steps (@ $5D8) must be at least one step greater then the IAC position vs coolant table (@ $5F5) steps for the ECM to fully control the idle speed." Tough to convey the exact meaning when I get excited over a major find
RBob.
In order to go closed loop idle the park/neutral input to the ECM must be in the 'Drive' position. While in park/neut there is no closed loop idle control.
BTW: we are talking about stock '7747 and '8746 code.
In order to go closed loop, besides the 'in drive' parameter, the kick down steps needs to be greater then the IAC vs. Coolant steps.
If the kickdown is 25 steps, and the coolant steps at 56C is 24, then at 56 C the ECM will go closed loop idle control. Same if the coolant steps at 56 deg are 10, the ECM will go closed loop shortly before reaching 56 C (interpolation between table entries puts the coolant steps at less then 25 before 56 C is reached).
OTOH: if the kick down steps are 15, and the lowest steps vs. coolant is 24, then closed loop idle will never happen.
Taking this statment of mine: The bottom line is that the kick down steps (@ $5D8) must be one step greater then the IAC position vs coolant table (@ $5F5) steps for the ECM to fully control the idle speed.
It should really read: "The bottom line is that the kick down steps (@ $5D8) must be at least one step greater then the IAC position vs coolant table (@ $5F5) steps for the ECM to fully control the idle speed." Tough to convey the exact meaning when I get excited over a major find
RBob.
Last edited by RBob; Apr 30, 2006 at 06:03 PM.
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I think I may have found out why my idle is so high. My laptop is charging right now, but, IIRC some of the steps are greater than the kickdown. I'll definatly look into that tomorrow.
One other thing. I'm still having a real rich startup issue, but I think I have figured that one out (tomorrow's cold start will tell). I raised mt O/L AFR to above 14.7 to one and when I started it this afternoon, it wasn't running so rich.
I raised my O/L AFR vs temp table to 13.00 across the board, and in the Cold AFR vs Kpa table I raised the values a bit, then in the Time Out vs Cool->(Choke sub'd from AFR) table I lowered the coldest values a bit. So after adding the values from O/L AFR vs temp table to the Cold AFR vs Kpa table (at 30 Kpa idle Kpa), and then subtracting the value from the Time Out vs Cool->(Choke sub'd from AFR) table, I'm ending up with a AFR value of about 15:1. I'm not sure why this is working, but it seemed to this afternoon.
We'll see what happens in the morning. 
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