graph LR
Engine{RPM} --> |= 0|EngineStopped(engine_running = false)
Engine{RPM} --> |> 0|EngineRunning(engine_running = true)

Temp{CTS} --> | < 80 |EngineWarming(warming = true)
Temp{CTS} --> | > 80 |EngineWarm(at_operating_temp = true)

graph LR  
Start{engine_running = true} --> Ready(Sample for 20s)
Ready --> QueryThrottle{Throttle < 4 degrees}  
QueryThrottle --> |Throttle Idle|EngineIdle(Engine Idle)
QueryThrottle -- Throttle Active --> QueryCruising{CTS > 80C}  
QueryCruising -- Engine Warm --> QueryCruiseIdle{RPM STD 5%}  
QueryCruiseIdle --> |Yes|IsCruising(Cruising) 
EngineIdle --> QueryTemp{CTS > 80C}  
QueryTemp -- Engine Cold --> QueryIdleCold{900 > RPM < 1200}  
QueryTemp -- Engine Warming --> QueryWarming{RPM = +Trend}  
QueryIdleCold --> |No|CTSFault(CTS or Thermostat Fault?)
EngineIdle --> QueryIdleOffset{Idle Offset < 100}  
QueryIdleOffset --> |No|IdleOffsetFault(Idle Error)
QueryTemp -- Engine Warm --> QueryIdleHot{10 > Idle Hot < 50}  
QueryIdleHot --> |No|IdleHotFault(Stepper Motor Fault?)

MemsFCR / ECU Communication Sequence

sequenceDiagram
autonumber
Note over MemsFCR, ECU: Initialisation
MemsFCR ->>+ ECU: Connect
ECU ->>- MemsFCR: Connected
MemsFCR ->>+ ECU: 0xCA
Note right of ECU: Initialise Command A 
ECU ->>- MemsFCR: 0xCA
MemsFCR ->>+ ECU: 0x75
Note right of ECU: Initialise Command B
ECU ->>- MemsFCR: 0x75 
MemsFCR ->>+ ECU: 0xF4
Note right of ECU: Heartbeat
ECU ->>- MemsFCR: 0xF4 
MemsFCR ->>+ ECU: 0xD0
Note right of ECU: ECU ID
ECU ->>- MemsFCR: 0x0D 0x99 0x99 0x99 0x99 
Note over MemsFCR, ECU: Request Dataframe Loop
loop Every second
activate MemsFCR
MemsFCR ->>+ ECU: 0x7D
Note right of ECU: Dataframe 0x7D
ECU ->>- MemsFCR: 0x7D XX XX XX.. XX
MemsFCR ->>+ ECU: 0x80
Note right of ECU: Dataframe 0x80
ECU ->>- MemsFCR: 0x80 XX XX XX.. XX
deactivate MemsFCR
end

MemsFCR Diagnostics Analysis Tree

graph TB  
Start{Is RPM > 0} --> |Engine is running| Ready(Sample for 20s)
Ready -- Every Second --> Ready  
Ready --> QueryMAP{30 > MAP < 60}
QueryMAP --> |MAP Invalid|MAPF(MAP Fault)
Ready --> QueryCPS{CPS = 0}  
QueryCPS --> |Crankshaft Position Invalid|CPSF(CPS Fault)  
Ready --> QueryCOIL{Coil Time < 4ms}  
QueryCOIL --> |Coil Time Too Long|COILF(Coil Fault)  
Ready --> QueryThrottle{Throttle < 4 degrees}  
QueryThrottle --> |Throttle Idle|EngineIdle(Engine Idle)
QueryThrottle -- Throttle Active --> QueryCruising{CTS > 80C}  
QueryCruising -- Engine Warm --> QueryCruiseIdle{RPM STD 5%}  
QueryCruiseIdle --> |Yes|IsCruising(Cruising) 
EngineIdle --> QueryTemp{CTS > 80C}  
QueryTemp -- Engine Cold --> QueryIdleCold{900 > RPM < 1200}  
QueryTemp -- Engine Warming --> QueryWarming{RPM = +Trend}  
QueryIdleCold --> |No|CTSFault(CTS or Thermostat Fault?)
EngineIdle --> QueryIdleOffset{Idle Offset < 100}  
QueryIdleOffset --> |No|IdleOffsetFault(Idle Error)
QueryTemp -- Engine Warm --> QueryIdleHot{10 > Idle Hot < 50}  
QueryIdleHot --> |No|IdleHotFault(Stepper Motor Fault?)

Idle Speed Diagnostic Tree

graph LR  
Start{Is RPM > 0} --> |Engine is running| Ready(Sample for 20s)
Ready --> QueryThrottle{Throttle < 4 degrees}  
QueryThrottle --> |Throttle Idle|EngineIdle(Engine Idle)
QueryThrottle -- Throttle Active --> QueryCruising{CTS > 80C}  
QueryCruising -- Engine Warm --> QueryCruiseIdle{RPM STD 5%}  
QueryCruiseIdle --> |Yes|IsCruising(Cruising) 
EngineIdle --> QueryTemp{CTS > 80C}  
QueryTemp -- Engine Cold --> QueryIdleCold{900 > RPM < 1200}  
QueryTemp -- Engine Warming --> QueryWarming{RPM = +Trend}  
QueryIdleCold --> |No|CTSFault(CTS or Thermostat Fault?)
EngineIdle --> QueryIdleOffset{Idle Offset < 100}  
QueryIdleOffset --> |No|IdleOffsetFault(Idle Error)
QueryTemp -- Engine Warm --> QueryIdleHot{10 > Idle Hot < 50}  
QueryIdleHot --> |No|IdleHotFault(Stepper Motor Fault?)

MAP Diagnostic Tree

graph LR  
Start{Is RPM > 0} --> |Engine is running| Ready(Sample for 20s)
Start --> |Engine off| EngineOff(Ignition On, Engine Off)
Ready -- Every Second --> Ready  
Ready --> QueryMAP{30 > MAP < 60}
QueryMAP --> |MAP Invalid|MAPF(MAP Fault)
EngineOff --> QueryMAPOff{MAP < 90}
QueryMAPOff --> |MAP Invalid|MAPF(MAP Fault)

O2 System Diagnostic Tree

graph LR  
Start{Is RPM > 0} --> |Engine is running| Ready(Sample for 20s)
Ready --> QueryTemp{CTS > 80C} 
QueryTemp --> |Engine is warm|WarmEngine(Operating Temp)
WarmEngine --> QueryLambdaStatus{Lambda Status = 1}
QueryLambdaStatus --> |No|LambdaInvalid(Lambda Fault)
WarmEngine --> QueryLambdaOsc{Lambda Oscillating?}
QueryLambdaOsc --> |No|LambdaInvalid
WarmEngine --> QueryLambdaVoltage{10mV > Lambda Voltage < 900mV}
QueryLambdaVoltage --> |No|LambdaInvalid

MemsFCR Log File Format and Applied Calculations to Raw Data

Column	Description	Calculation Applied
#time	event timestamp hh:mm:ss.sss
80x01-02_engine-rpm	engine rpm
80x03_coolant_temp	temperature in degrees Celsius read from the Coolant Temperature Sensor (CTS). This sensor can be found under the injector unit. An essential value in the air:fuel ratio calculation	value - 55
80x04_ambient_temp	not used by the ECU, always returns 255	value - 55 = 200
80x05_intake_air_temp	temperature in degrees Celsius read from the Air Intake Temperature Sensor (ATS). This sensor can be found under the air filter. An essential value in the air:fuel ratio calculation	value - 55
80x06_fuel_temp	not used by the ECU, always returns 255	value - 55 = 200
80x07_map_kpa	manifold absolute pressure (MAP). Reads pressure from back of the injector unit via the vacuum pipes and fuel trap. An essential value in the air:fuel ratio calculation
80x08_battery_voltage	the battery voltage. A figure <12 volts will cause running issues	value / 10
80x09_throttle_pot	throttle potentiometer position. used by the ECU do determine throttle position when controlling idle speed	value * 0.02
80x0A_idle_switch	shows the state of the throttle switch, fitted on early vehicles. On systems without an actual throttle switch the value shown indicates whether the MEMS ECU has calculated that the throttle is closed by using the throttle position sensor. If the switch shows 'ON' when the throttle is closed, then the vehicle will not idle correctly and the closed throttle position may need to be reset. This procedure is performed by fully depressing and releasing the accelerator pedal 5 times within 10 or less seconds of turning on the ignition and then waiting 20 seconds.
80x0B_uk1	unknown value
80x0C_park_neutral_switch	used on vehicles with an automatic gearbox	true / false
80x0D-0E_fault_codes	ECU fault codes: Coolant temp sensor fault (Code 1) Inlet air temp sensor fault (Code 2) Fuel pump circuit fault (Code 10) Throttle pot circuit fault (Code 16)
80x0F_idle_set_point	adjusts the idle rpm by the value shown. Adjusting idle speed will modify this value
80x10_idle_hot	the number of IACV steps from fully closed (0) which the ECU has learned as the correct position to maintain the target idle speed with a fully warmed up engine. If this value is outside the range 10 - 50 steps, then this is an indication of a possible fault condition or poor adjustment.	value - 35
80x11_uk2	unknown value
80x12_iac_position	Inlet Air Control valve (IACV) position (relates to expected Stepper Motor position)
80x13-14_idle_error	idle speed offset (also known as idle speed deviation)
80x15_ignition_advance_offset	adjustment to the ignition timing
80x16_ignition_advance	ignition advance, value of 128 = 0	(value / 2) - 24
80x17-18_coil_time	coil timing in ms	value * 0.002
80x19_crankshaft_position_sensor	position of the crankshaft from the position sensor (CPS)
80x1A_uk4	unknown value
80x1B_uk5	unknown value
7dx01_ignition_switch	status of the ignition switch	true / false
7dx02_throttle_angle	shows the position of the throttle disc obtained from the MEMS ECU using the throttle potentiometer. This value should change from a low value to a high value as the throttle pedal is depressed.	value * 6 / 10
7dx03_uk6	unknown value
7dx04_air_fuel_ratio	the current air:fuel ratio	value / 10
7dx05_dtc2	diagnostic trouble code - unknown codes
7dx06_lambda_voltage	the voltage read from the lambda sensor	value * 5
7dx07_lambda_sensor_frequency	not used by the ECU, value reads 255
7dx08_lambda_sensor_dutycycle	not used by the ECU, value reads 255
7dx09_lambda_sensor_status	ECU O2 circuit status, 1 active
7dx0A_closed_loop	ECU has entered closed loop and uses the lambda sensor for determining air:fuel ratio
7dx0B_long_term_fuel_trim	long term fuel trim (LTFT) displays ECU value to adjust fuelling. value of 128 = 0	value - 128
7dx0C_short_term_fuel_trim	short term fuel trim (STFT) displays ECU value to adjust fuelling
7dx0D_carbon_canister_dutycycle	not used by ECU, value reads 0
7dx0E_dtc3	diagnostic trouble code - unknown codes
7dx0F_idle_base_pos	the base value to offset idle position from
7dx10_uk7	unknown value
7dx11_dtc4	diagnostic trouble code - unknown codes
7dx12_ignition_advance2	ignition advance	value - 48
7dx13_idle_speed_offset	idle speed offset used to adjust idle speed
7dx14_idle_error2	idle error
7dx14-15_uk10	unknown value
7dx16_dtc5	diagnostic trouble code - unknown codes
7dx17_uk11	unknown value
7dx18_uk12	unknown value
7dx19_uk13	unknown value
7dx1A_uk14	unknown value
7dx1B_uk15	unknown value
7dx1C_uk16	unknown value
7dx1D_uk17	unknown value
7dx1E_uk18	unknown value
7dx1F_uk19	unknown value
0x7d_raw	hexadecimal response from the ECU for command 0x7D
0x80_raw	hexadecimal response from the ECU for command 0x80
engine_running	engine is running	true / false
warming	engine is warming up to operating temperature	true / false
at_operating_temp	engine is at operating temperature	true / false
engine_idle	engine is idle	true / false
idle_fault	hot or cold idle speed or idle offset is outside expected parameters	true / false
idle_speed_fault	cold idle speed is outside expected parameters	true / false
idle_error_fault	idle offset is outside expected parameters	true / false
idle_hot_fault	hot idle speed is outside expected parameters	true / false
cruising	rpm is stable but not idle; engine is cruising (differentiates from idle)	true / false
closed_loop	ECU is operating in closed loop (using lambda to determine air:fuel ratio)	true / false
closed_loop_expected	expecting the ECU to be in closed loop	true / false
closed_loop_fault	closed loop fault	true / false
throttle_active	the throttle pedal is depressed	true / false
map_fault	MAP readings is outside expected parameters	true / false
vacuum_fault	MAP and Air:Fuel ratio are outside expected parameters indicating a possible vacuum pipe fault	true / false
iac_fault	IAC position invalid if the idle offset exceeds the max error, yet the IAC Position remains at 0	true / false
iac_range_fault	IAC readings outside expected parameters	true / false
iac_jack_fault	high jack count indicating possible problem with the stepper motor, throttle cable adjustment or the throttle pot	true / false
o2_system_fault	detected a potential o2 system fault	true / false
lambda_range_fault	lambda sensor readings are outside expected parameters	true / false
lambda_oscillation_fault	lambda sensor not oscillating as expected	true / false
thermostat_fault	coolant temperature changes over time indicate thermostat fault (could also be a CPS fault)	true / false
crankshaft_sensor_fault	crankshaft position sensor (CPS) reading is outside expected parameters	true / false
coil_fault	coil is outside expected parameters	true / false