I'll have to check mine and see what it reports but I recall on my old '07 Focus even during the frigid winter months Torque would report it going closed loop pretty quickly around 15-20 seconds in from initial start. Seemed based on that that it only cared about the O2 sensors getting up to usable temp.
Hopefully I'll be able to take mine out this weekend and verify after all our snow starts melting. Sadly haven't driven mine all week due to shitty snow management by our city. Our cul-de-sac has been untouched since our major snowfall and freezing rain last Friday. Tried going out Monday and got stuck 2 feet from the edge of my driveway. Have had to commute with my brother only because he has an AWD SUV with brand new tires and even then it is sketchy getting into our neighborhood.
Here's what I believe happens. The O2 sensor heaters ramp up quickly to a temperature above the closed loop heater control temperature. The O2 sensors temperature is then allowed to fall to the closed loop heater control temperature (based on measured impedance) and the O2 sensor temperature (impedance) is now controled around that temperature. The heater is now in closed loop operation and the PCM will enter closed loop fuel operations if other entry conditions are met. The closed loop heater control happens fairly quickly which is likely the 15 seconds or so.
But the fuel trim and other monitors do not start operation until closed loop O2 heater operation, specific coolant temperature and certain other paramenters are met. "If the heated oxygen sensors (HO2S) are warmed up and the PCM determines the engine can operate near stoichiometric air to fuel ratio (14.7:1 for gasoline), the PCM goes into closed loop fuel control mode." -service manual.
From the Ford OBD System Operation Summary for Plug In and Hybrid Electric Vehicles document:
"During closed loop operation, short term fuel trim values are calculated by the PCM using oxygen
sensor inputs in order to maintain a stoichiometric air/fuel ratio. The PCM is constantly making adjustments to the
short term fuel trim, which causes the oxygen sensor voltage to switch from rich to lean around the stoichiometric
point. As long as the short term fuel trim is able to cause the oxygen sensor voltage to switch, a stoichiometric
air/fuel ratio is maintained.
When initially entering closed loop fuel, SHRTFT starts 1.0 and begins adding or subtracting fuel in order to
make the oxygen sensor switch from its current state. If the oxygen sensor signal sent to the PCM is greater than
0.45 volts, the PCM considers the mixture rich and SHRTFT shortens the injector pulse width. When the cylinder
fires using the new injector pulse width, the exhaust contains more oxygen. Now when the exhaust passes the
oxygen sensor, it causes the voltage to switch below 0.45 volts, the PCM considers the mixture lean, and
SHRTFT lengthens the injector pulse width. This cycle continues as long as the fuel system is in closed loop
But, the fuel monitor (and other monitor like the Air/Fuel ratio monitor) has the entry conditions below. When the engine is "too" cold, the PCM will run the air / fuel mixture rich. So, the monitors won't run under 155F as the engine may not be running near the stoichiometric A/F ratio and "incorrectly" trigger a fault condition.
Engine Coolant Temp ...155F .....230F
Intake Air Temp ............-40F ......150F
Engine Load .................30%
Purge Duty Cycle.......... 0% ........0%
Fuel Level...................... 15%"
IMO, the computed fuel used would be more difficult to quantify when ECT is less than 155F. Since the OP indicates city driving with stops there's a good chance ICE coolant temperture is under 155 F a lot of the time in very cold weather.
OP, you need grille covers to help raise coolant temperatures.
Edited by Plus 3 Golfer, 21 January 2018 - 09:27 AM.