Hello
The trick of a resistor in the IAT (Intake Air temperature connector)
does not work with SP95 because when indicating to the ECU that the air is colder than the reality, the ECU makes the fuel mixture a little bit more rich .... but the O2 sensor (or lambda sensor) sees that slightlly enriched mixture and opens a little less the injectors. So the overall result is NIL
But with E85, without any other modification, the mixture is naturally poor by some 30%-40% ...
so when indicating to the ECU that the air temperature is 40, 50 or 60 degrees below the reality it is possible to enrich the mixture by some 15, 20 or 25% .. as good as adding 1, 1.5 or 2 bars on the fuel pressure regulator
Why does that trick work ?
because when reading (sorry only in French)
http://www.thermexcel.com/french/tables/massair.htm you can see that air density is higher when cold. Sibling values are given in
http://en.wikipedia.org/wiki/Density_of_air roughly
1,34g per liter at -10°C
1,29 at 0°
1,24 at 10°
1,20 at 20°
1,15 at 30°
so it should be around
1,44g per liter at -30° C
1,39 g per liter at -20°C
For 100 liters of air entering thru
a vane meter sensor, when reading -30°C on the IAT sender, ECU will then call for 1.44 *100/14.7 = 9,79g of fuel
If the external temperature is in fact +10°C, that is to say with 1.24g/air liter … it should only call for 1.24*100/14.7 = 8,43g of fuel … so with the additional resistor fitted in the IAT sender connector .. the overall enrichment is roughly around +16%
If the external temperature is in fact +20°C/+30°C ... then the overall enrichment is around 20/25% respectively
Not a too bad result with a such an easy to do modification ... unplug the IAT sensor and fit a resistor in its connector : done ... provided the outside temperature is always above +10°C
As with E85, the mixture is poor by some 30-40%, the O2 sensor will in fact appreciate this enrichment and not play against
Such a modification does not work in cars having a hotwire mass air flow sensor because their ECU do not take into account the air temperature ...
It works very well in case of Air Vane Meter sensor ( see
http://en.wikipedia.org/wiki/Mass_flow_sensor ) because air density is used to compute the air mass entering the engine
It works also a little bit in MAP sensor (
http://en.wikipedia.org/wiki/MAP_sensor ) where temperature is used to correct MAP
When so doing, the resistor should be selected with caution because many ECUs, when reading an air temperature of say -40°C will consider the sender is not running properly and have its indication replaced by a fixed value (e.g. the water temperature at cold start)
Of course it is easier to play that trick in the South of Spain that in North of Europe ... sorry for the Swedes .. and it works better and better with hot air taken from the engine bay and not from the outside ... playing again the same game as "tuning" people with a washable air intake located in the engine bay
Any comment ?
Bye
Best