Jeep Strokers

Being new to tuning the OBD I system I decided to put together as much information as I can on how it works. Starting with the various engine operating modes, what triggers the transition between modes and what sensors are operating in each mode. I have put the following together as a summary of informaton collected from this site and a few others. I am posting it FIRST OF ALL TO CHECK AND SEE IF IT IS CORRECT. Please correct what you KNOW to be wrong.

After I get this nailed down then I will move on to the various "tricks" that can be used to adjust OBDI systems in each mode.


Open Loop
O2: NO
MAP: Yes
TPS: Yes
IAT: Yes.
Coolant Temp: Yes
Crank Pos. Sensor: Yes for FI & Ign timing
Cam Pos. Sensor: Yes for FI & Ign timing

Closed Loop
O2: Yes
MAP: No
TPS: No
IAT: (Yes?)
Coolant Temp: No
Crank Pos. Sensor: Yes for FI & Ign timing
Cam Pos. Sensor: Yes for FI & Ign timing

2. Mode Two: engine start-up (crank)--open loop.
Pre programmed injector pulse width
TPS-Not sure if this used on start up.
IAT-Not sure if this used on start up
Coolant temp: Senses cold engine & forces open loop.
(does a hot engine start in open loop?)

3. Mode Three: engine warm-up--open loop.
Pre programmed injector pulse width adjusted by active sensors.
TPS-add fuel as throttle opens
IAT-add fuel for air colder than baseline, remove fuel for air warmer than baseline
Coolant temp: remove fuel as engine warms up

4. Mode Four: engine idle (at normal operating temperature)--closed loop.
Transition to closed loop controlled by water temp sensor ~180 deg min.
02: add fuel for low voltage, remove fuel for high voltage (digital steps rich/lean) to maintain 14.7:1 average.
Number of rich & lean readings are averaged over a short and long term period and compared. Adjustments made to fuel in an attempt to match long & short term averages.
IAT: Not sure if IAT is used in closed loop mode.

5. Mode Five: cruise (at normal operating temperature)--closed loop.
Transition to closed loop controlled by water temp sensor ~180 deg min.
02: add fuel for low voltage, remove fuel for high voltage (digital steps rich/lean).
Number of rich & lean readings are averaged over a short and long term period and compared. Adjustments made to fuel in an attempt to match long & short term averages.
IAT: Not sure if IAT is used in closed loop mode.
TPS: Not sure if TPS is used in closed loop but I suspect that it is. 35mph cruise and 75mph cruise need different amounts of fuel. TPS below 70%.

6. Mode Six: deceleration--open loop.
Transition into Mode 6 open loop controlled by?
No informaton on what sensors area active.

7. Mode Seven: WOT--open loop.
Transition into Mode 7 open loop controlled by TPS showing >~70% throttle open
Pre programmed injector pulse width adjusted by active sensors
TPS: 70 to 100%. More fuel with more throttle.
MAP: Lower MAP more fuel
IAT: Provide more fuel with air colder baseline, less fuel with air hotter than baseline

CPS, Cam position sensor, MAP, TPS, IAT, and CTS inputs are used all the time but the CTS assumes a lower place in the hierarchy once the engine has warmed up and the O2 sensor inputs are used to set the A/F mixture in closed loop mode.
The MAP sensor is the principle load sensor and its signal is required so that the PCM can adjust the injector pulse width as manifold absolute pressure changes.
The TPS is also an important load sensor and its signal is required so that the PCM can adjust the injector pulse width as throttle position changes. Under acceleration the ECU stays in closed loop until the TPS is past 70%.