Nissan ECU Tuning

BlackZ · Joined: 05 Dec 2007 Posts: 1

Hi

I have found a number of posts talking about the temperature that the stock Z fan comes on at and I know the addresses to change (7443 & 7442) but cannot figure out the scaling for the numbers.

For example the stock map has a value of 0x8C and the fan comes on at exactly 105C (tested)

I have looked at another map that has the fan come on at 85C and the value is 0x78 I cannot seem to find a formula for calculating the temperature

Does anyone know the formula.. I want a turn on of about 95C.

Eric · Joined: 17 Nov 2003 Posts: 258 Location: Holland

> Does anyone know the formula.

it's not so much of a formula, but more a (complicated) lookup routine.

anyway, i'll try to explain it in short:

Main variables:
0x7443 (stock value : 8C) is fan activation temperature offset with aircon off
0x7442 (stock value : 8C) is fan activation temperature offset with aircon on
3 byte table at 0x77ED (stock values : 00 00 00), defines the fan activation in relation to vhclspeed with aircon off
3 byte table at 0x77F0 (stock values : D4 D4 00), defines the fan activation in relation to vhclspeed with aircon on

Operation:
from the 3 byte tables, the 1st byte is selected when vhclspeed is between 0 and 20kmh, the 2nd byte when speed is between 20 and 40km, the 3rd byte when speed exceeds 40kmh

the selected byte of these tables is then split into 4 sets of 2 bits:
eg. stock value of 0xD4 (= 11 01 01 00)

the 1st set (00) is selected when temperature is below value of 7443 or 7442 minus 50 (< 90C)
the 2nd set (01) is selected when temperature equals/exceeds value of 7443 or 7442 minus 50 (>= 90C)
the 3rd set (01) is selected when temperature equals/exceeds value of 7443 or 7442 minus 45 (>= 95C)
the 4th set (11) is selected when temperature equals/exceeds value of 7443 or 7442 minus 40 (>= 100C)

meaning of the 2 bit sets:
11: fan on full blow , 01: fan on half blow (TT only), 00: fan off

the routine has 2 major overrides: if temperature equals/exceeds 105C (value of 7443 or 7442 minus 35) or if the ecu is in failsafe mode for whatever reason (eg. temp sensor disconnected) , then the fan is always turned on at full blow no matter what the vhclspeed is.

> I want a turn on of about 95C.

easiest/nicest way is to modify the small 3 byte table at 0x77ED.
change the values of this table to D0 D0 00

this will turn on the fan at half blow at 95C
once temp gets 100C or higher the fan will turn on at full blow

if you want to have the fan on full blow at 95C (eg. because your car is a NA), the table should contain : F0 F0 00

Hope this helps..

-Eric
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DTA-motorsport