'747 idle control

[steve ravet]

Thanks for the explanation Bob!  In your case, if the engine got to 158
and idle control starts at 133, then why didn't it control your idle? 
Is kickdown the same as "idle flare", where the engine revs up then
slows down right after you start it?

Also, (re-reading your idle strategy article), you descibe a process
where after startup, the IAC is moved to a particular position based on
coolant temp.  Once it gets there idle control takes over.  Is the table
below the one that defines this initial position of the IAC?

It sounds like now the process is idle flare, then IAC moves to it's
initial position based on the table below.  There is no idle control
until the coolant rises above the temp specified by $53f, at which point
the only control is an upper limit specified by $5e1.

Full idle control isn't achieved until the "kickdown" value is larger
then the position value specified in the table below, based on coolant
temp.

Do you have any insight into why this algorithm is used?  If this table
and the kickdown value are only used at startup why do they figure into
when full idle control is enabled?

thanks,
--steve

rr wrote:
> 
> 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 posiiton
> vs coolant table:
> 
> *==============================================
> * 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.
> 
> BobR.
> 
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-- 
Steve Ravet
steve.ravet at arm.com
ARM,Inc.
www.arm.com
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