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Re: quattro-digest V3 #813
>I also "fixed" the ECU to smooth out the warm-up open-loop
>mixture shenanigans . . . )
I would be interested in hearing how .....please.
In the MAC-02, the static/openloop mixture (FreqValve duty cycle) is con-
trolled via the table(s):
; Block temperature => Index-8 map, used to determine cold engine open
; loop warmup mixture (Pg 24 -- warmup frequency valve duty cycle ).
; Values are A/D converted:
; 0xE0 = TBD
; 0xC4 = -20C / -4F (by the book; empirically ~ +10F)
; 0xA7 = -10C / 14F (by the book; empirically ~ +25/30F)
; 0x89 = 0C / 32F
; 0x7A = 10C / 50F
; 0x6C = 20C / 68F
; 0x5C ~ 25C / 77F
; 0x53 ~ 32C / 90F
; 0x40 ~ 38C / 100F
; 0x1D ~ 60C / 140F
F190: C4=196 A8=168 89=137 7A=122 6C=108 67=103 5A=090 55=085
; Table of cold engine open-loop FreqValve duty cycle values, indexed by
; BlockTempMap8 index, with last entry also doubling as a general-purpose
; "open-loop" default.
; Values (8-bit) percentage (duty cycle):
; 0x41 = 65%
; 0x3C = 60%
; 0x37 = 55%
; 0x32 = 50%
; 0x2A = 42%
F198: 50=080 41=065 3C=060 37=055 32=050 25=037 25=037 32=050
Right around 70-80F block temp, the map dips way *WAY* down to 37% duty
cycle (way lean), before jumping back up to 50% (nominal), just before
going closed-loop (at around 95F block temp, O2 sensor willing).
My observations are two-fold: one -- exactly at the 37% dip the engine
starts running like cold lumpy s**t (easy to watch with your trusty
duty-cycle meter (CP7678???) hooked up), and smooths out again as the
mixture goes back up to 50%; two -- when the system goes closed-loop
the ECU seems to like to run a little rich (typically around 52-55% duty
cycle, in my observations) for awhile till it finishes warming up.
Running a Schrick cam exacerbates the problem; the Schrick definitely
likes a richer cold mixture!
Thus, I made two changes to the map -- I stretched the temp range a little
to run out to 120F or so before permitting closed-loop, and I didn't drop
the duty cycle below 50%.
(Also note that the trailing 50% entry is also the "test point" value for
closed idle and WOT switches simultaneously, so you want it to be 50 al-
Note: the above is the "F" ROM decoding; the "B" (earlier) ROM is similar