INJECTOR CONTROL
The computer activates the fuel injector(s) to control fuelmetering by varying the injector driver's pulse width and frequency.The pulse width and frequency is a function of the computer sensed inputs as defined by the system application.
Two modes of active control are possible:
  •  open loop and,
  •  closed loop.
    • Using information from the oxygen sensor. The mode control is determined by the computer's ability to measure the exhaust oxygen content. If the exhaust oxygen content cannot be measured, the computer controls fuel injection in the open loop mode. In the closed loop mode when a rich air/fuel ratio is detected, the injector control duty cycle is decreased to cause a leaner air/fuel mixture, and vice versa for a lean air/fuel ratio.
    If the computer malfunctions, fuel control is performed in the open loop mode by the Backup fuel circuitry within the PCM (see Backup fuel Control).The PCP flag for paragraph 3.3.6 identifies an emissions related function and applies over the temperature range of 0 c to 40 c and a battery voltage of 11 to 16 V.
    The ability of the injector outputs to turn on and off meeting the pulse width accuracy should be verified (see computer control)

    The PCP flag also identifies a safety related feature of back-up fuel.The ability of back-up injector control should be verified (see Backup fuel Control).The two low side fuel injector drivers may be operated in the following modes (base PCM P/N 16127470).The base model operates in the ramp and hold mode.

    MODE
    		  
    Notes
    1
    Alternating TBI
    Both injectors used
    2
    Single Injector TBI
    2nd injector driver not connected
     

    Alternate base models can be derived which provide these additional fuel modes.These applications would require Hi-impedance injectors to run ramp and hold, on the removal of the 0.1 ohm current sample resistor and replacing it with a zero Ohm jumper (R194 and R199) to operate in the saturated mode.

     
    MODE
    		  
    Notes
    3
    4 Cyl PFI
    		  
    4
    6 Cyl PFI
    		  
    5
    8 Cyl PFI
    Modes 1 through 5 are for ECU controlled fuel pulses
    PFI/TBI MODE SELECTION
    To set the PFI/TBI modes just described, the MEM/CAL assembly resistors R29 and R30 must be set to proper values. These two resistors form a voltage divider network between a 5 volt line, VRFD, and ground which enables decoding the REFHI input signal according to the mode selected.

    The divided input voltage level and its relationship to the injector operating mode is shown in the table below, MEM/CAL Mode Selection.

    The mode selected also has a critical relationship to ignition spark events, EST output, as described in Ignition, Spark and Dwell Control.

     
     
    MEM/CAL 
    Mode Selection
    Application Mode Input Voltage(R29/R30 ratio) Frequency Of Injection
    1. Alternating TBI 2/3 VRFD + 10% ALT. Every REF pulse
    2. Single Injector TBI VRFD + 0% - 10% Every REF pulse
    3. 4 Cyl. PFI 2/3 VRFD +/- 10% Every 4th REF pulse
    4. 6 Cyl. PFI 1/3 VRFD + 10% Every 3rd REF pulse
    5. 8 Cyl. PFI GND -0% + 10% (5v) Every 4th rd REF pulse
     
    Note:
    Applications 3 thru 5 require alternate base models to operate in The saturated drive mode. Only peak & hold modes are permitted with this base model.
     
    Computer Control
    Injector fuel pulses, under software control, can occur synchronous or asynchronous to the DRP (distributor reference pulses). Synchronous operation occurs during vehicle steady state conditions while asynchronous operation occurs during transient conditions such as acceleration, certain start up. conditions and coast down conditions.In synchronous operation sane of the modes allow the start of injection to be delayed frat the REF pulse as-a function of software.PCP flag requires verification of pulse width accuracy over 00C to 400C, battery voltage 11 to 16 V.
    The following pulse width and pulse delay accuracies apply over the normal Computer voltage range (6.3 to 16 V) and the operating temperature range (-40 C to 850C).

     

    Injector pulse width/Delay Accuracies (Computer Controlled)
     
    Synchronous Operation
    Limits
    A
    Pulse width range
    0 to 499.98 usec
     
    Computed accuracy
    (for 1 Count = 15.26 usec)
    +2, -1 Count
     
    Computed width
    plus driver switching delays
    +58 to -15 usec
     
     
     
    B
    Pulse delay range:
    0 to 499.98 usec
     
    Computed accuracy:
    (For 1 Count = 15.26 usec)
    +2, -1 Count
     
    Computed delay
    Plus driver on delay
    +58 to -15 usec
     
    Added delay*
    (REFA to ECU)
    93 to 73 usec
     
    Asynchronous Operation
    Limits
     
    Pulse width 
    0 to 499.98 usec
     
    Computed accuracy
    (for 1 Count = 15.26 usec)
    +2, -1 Count
     
    Computed width
    plus driver switching delays
    +58 to -15 usec

     
    NOTE:
    A time delay from the fall of REF A input signal to the Ear results from RC filtering and circuit switching times. Time delay indicated results at REFA equal to 5V (VOH)
    Fuel Control During Crank
    Fuel injector pulses occur during engine cranking conditions under computer control or backup control. Computer control is the primary mode of operation. Backup control can take place when the battery voltage falls below 6.3 V or will occur when the computer software malfunctions.


    Backup Fuel Control
    The PCM provides backup i njector control upon detection of a digital processing failure (see computer operational tests), or when the battery voltage falls below 6.3 VDC  Injector pulses occur synchronously to the REF distributor pulses. Fuel pulse width is a function of coolant temperature, load input (MAP or TPS), ignition voltage and crank or run engine speeds. Key function/features include the following.

      1. Fuel pulse width during crank or run conditions
      2. Battery voltage/fuel pump compensation
      3. Crank/run selection
      4. Crank enleanment
      5. Add-on timer
      6. Clear flood
      7. Outputs disabled
    Outputs Inhibited During Backup Fuel
    During Backup fuel mode all outputs are disabled except as noted here. The outputs active are:
    Pulse width Calibration
    Backup calibration is contained in the MEM/CAL assembly in the form of thirty resistors in two resistor networks. To determine resistor values refer to TSO CT MANUAL $RFDCAL procedure.
    Table 17 provides a typical set of calibration resistor values and Table 18 provides pulse widths at selected conditions for these values. The pulse widths are presented as reference and verify back up performance. These values do not necessarily represent a production set of calibration values.
     
    Pulse width Accuracy
    Pulse width measurements compared to calculated pulse widths of $RFDCAL.
    4.5V to 16 V, -400c to 850C.
    Pulse width accuracy: + 15%
     
    Resistors Forming Injector Pulse width
    The basic pulse width is established by the resistors R1 through R14 within the NEM/CAL networks.
    In the crank mode, the pulse width is a function of coolant temperature. Network resistors R1 through R5 provide the proper curve shaping calibration and R6 provides the scaling calibration. In the run mode, R7 provides scaling calibration and R8 provides additional scaling calibration. Scaling between run and crank are independent and are a function of r6 and R7 respectively.
     

    Load Shaping and scaling During the run mode resistors Rl3 and R14 establish the base pulse width. Resistors R9, R10 and R11 provide shaping while R12 provides scaling functions that act to modify the base pulse width.

    Battery Voltage/Fuel Pump Compensation

    This function provides compensation for lower fuel pressure due to decreasing battery voltage driving the fuel pump. It increases the injector pulse width as the ignition voltage, law, decreases. The base pulse width is multiplied lx, l.5x or 2X depending upon the selection of resistor values R22, R23 and R24 and IGNN voltage. Ignition voltage, lGNN, is the voltage source for the series string R22, R23 and R24. As IGNN decreases the voltage nodes formed by the resistors decrease in reference to the regulated 5V line, VRFD. Multiplier 1x is enabled when the voltage nodes of both R23-R24 and R22-R23 are above 1/3 VRFD. Multiplier 1.5x is enabled when voltage node of fl3-~4 is below 1/3 VRFD and voltage node PU2-R23 is above VRFD. Multiplier 2x is enabled when both voltage nodes are below 1/3 VRFD. Fuel pump compensation is eliminated by making R24 equal to 1 meg ohm.
     
    Run/Crank Selection
    The determination of run or crank conditions is accomplished by monitoring the engine speed via the REF distributor input signal. Resistor R21 and a 0.1 ufd capacitor form a one-shot oscillator, along with a counter, provides a time base comparison to engine speed. RFDCAL computes the value of R21i for requested crank or run engine speeds. The hystersis or difference between crank to run engine speed and run to crank engine speed is a multiple of 4.
     
    Crank Enleanment
    This feature provides leaning out the fuel after five engine revolutions have occurred. For each revolution following the fifth revolution the pulse width is decremented by art; amount set by resistor R16 (R18 must be open). The pulse width can be decremented up to 31 times depending upon the coolant calibration temperature and calibration values. Above or below this temperature the minimum pulse is ratiometric to the crank calibration curve. The clamp at the voltage node formed by Rl5 and a 10 K ohm pull up controls the minimum pulse width. The voltage at this node must be.set:to100 mv or greater. To prevent crank enleanment R16 must be open and R18 must be set to 10 K ohm.

    Add-on-Timer
    The add-on timer is typically used on PFI applications to modify injector pulse widths to compensate for changing injector opening times resulting from changes in battery voltages. The add-on timer occurs before the fuel pulse is initiated. Resistors R17 and R19 in-conjunction with R20 and IGNN voltage control this feature.

    Clear FloodThe clear flood function inhibits fuel pulses when the throttle position opening exceeds 60% during the crank mode. The switch point is set to 60% of VRFD with a tolerance of +/-10%.

     
    Table 17 
    $RFDCAL Backup Fuel That Calibration
    (Typical values in Ohm)
    Ref Des Value   Ref Des Value   Ref Des Value
    R1 147.0K   R11 22.1K   R21 383.0K
    R2 11.3K   R12 237.0K   R22 25.5K
    R3 34.0K   R13 511.0K   R23 681
    R4 14.3K   R14 73.2K   R24 5.49K
    R5 2.1 MEG   R15 Short   R25 16.5K
    R6 23.2K   R16 Open   R26 24.9K
    R7 10.0K   R17 154.0K   R27 Short
    R8 75.0K   R18 10.0K   R28 OPEN
    R9 80.6K   R19 3.09K   R29 20K
    R10 536.0K   R20 15.8K   R30 10K
    Table 18 
    $RFDCAL Test Pulse Widths, 250c
    Battery voltage = 12 volts, 4K pull up. $RFDCAL values.
    Coolant = Deg c
    MAP = Kpa
    Pulse width in msec.
    Coolant Temp Crank
    MAP=100    		 Run
    MAP=50    		 MAP
    Press.    		 Run
    Cool+20    		 Run
    Cool+90
    -20 74.5 10.3 100 11.3 7.9
    -10 48.1 8.9 90 10.1 7.1
    0 8.9 7.6 80 9.0 6.3
    10 23.9 6.4 70 7.8 5.5
    20 18.7 5.6 60 6.7 4.7
    30 15.6 5.0 50 5.6 4.0
    40 13.7 4.6 40 4.5 3.2
    50 11.5 4.3      
    60 11.8 4.1      
    70 11.3 4.0      
    80 11.1 4.0      

    TBI INJECTOR DRIVER CHARACTERISTICS

    TBI Applications
    In TBI applications, the drivers operate in the peak and hold (1 A) mode provided the battery voltage is sufficient to reach the peak (4 A) condition. The injector loads, A and B, are connected from switched battery to injector driver outputs INJA/ and TNJB/ respectively. NEM/CAL mode select (R29/R30) must be hardware programmed for TBI applications as described in, Table 18. Also, software must command the PMID via an internal signal (M/CLR), to control injector current in the peak and hold node. N/CLR must be a logic zero for this application. As noted, specific applications may delete one driver if required.

    TBI Output Current Profiles
    Injector current profiles are shown in Figures 2 and 3. The current rise time will vary as a function of injector solenoid inductance and resistance, the battery voltage and to a lesser degree the driver saturation voltage which varies with temperature.  The driver operates in the saturated mode until the 4 A peak is sensed and then regulates to 1 A during the hold mode as shown in Figure 3. Decreasing the injector resistance will permit the peak current to be realized at a lesser voltage than shown in Figure 3, which illustrates the current wave shape for an injector resistance equal to 1.0 ohm. It must be-noted, Figures 2 and 3 reference 6.5 V as the voltage threshold below which the peak current may not- be realized. This assumes no external voltage drops occur relating to the injector wire harness and the PCM ground harness. In practice, and testing, this minimum value is not universal, and should be evaluated using the "TB! Output Voltage" section, which identifies driver performance.

    TBI Output Voltages
    The output voltage from the injector driver(S), signals INJA/ and INJB/, during the saturated portion of the peak and hold mode is expressed below as VOUT/ Were:RPCM = (RDSON + RCKT.BD +RCONT.CONT + RSAMPLE) RH = Resistance of external injector harness and PCM Ground harness.

    RINJ = Resistance of injector load
    The PCM's saturated mode on resistance (RPCM) during activation time is tabulated below.
    Table 19
    Maximum Peak and Hold Saturation Resistance * (Ohms)
    For VBAT = 4 5 to 16V
    IINJ eq or lt 5Amp (reference value)
    Temperature
    -40c
    25c
    85c
    RPCM(MAX) Ohm
    0.45
    0.50
    0.65

    The minimum battery voltage required to achieve the 4Amp peak condition can be calculated in general from the following:VBAT (min = 4 Amp (RH + RINJ + RPCM)Note:The 4 Amp condition is the typical value, not worst case.

    Injector Clamping
    The injector driver clamp limits the voltage-across the driver to protect it and to ensure a fast injector turn off. he clamp circuit utilizes the driver as a power zener in this mode. Clamp voltages tabulated below are for battery voltages of 6.3 to 24.5V. A minimum clamp voltage of 49V can result when the~ battery voltage is less than 6.3 V.Injector Clamp Voltage = 86 +/- 14V (6.3V lt. VBAT 24.5 V)

    Current Performance Accuracy
     
    Limits
    0c to 40c
    Limits 
    -40c to 0c
    +40c to 85c
    I peak, Amps
    3.6 - 4.4 A
    3.2 - 4.8 A
    I hold, Amps
    0.9 - 1.1 A
    0.8 - 1.2 A
    Current Leakage at 16 VDC is less than 500 uamp.
    Notes:

    Current Performance Accuracy
     

     

     
    Limits
    0c to 40c
    Limits 
    -40c to 0c
    +40c to 85c
    I peak, Amps
    2.0 - 4.4 A
    2.0 - 4.8 A
    I hold, Amps
    0.9 - 1.1 A
    0.8 - 1.2 A
    Current Leakage at 16 VDC is less than 500 uamp.
     
    Notes: