Starion Fuel System Primer

Starions use throttle body injection with two injectors, either alternate firing 500cc (50lb+/-) injectors in < 86.5, and primary 600cc + secondary 1000cc in 86.5 and up. The system uses inputs from air mass meter, air temp sensor, throttle position, manifold absolute pressure (MAP), engine rpm from coil -, water temp, vehicle speed sensor, and O2 sensor (in closed loop mode) to regulate injector pulse time and secondary injector startup to adjust fuel quantity.

The air flow meter is a Karmann vortex sensor. The greater the air mass flowing thru the meter, the larger the number fo vortices formed in the flow, and the vortices are counted by an ultrasonic beam crossing the air flow path. Only a portion of the airflow is metered, with the balance bypassing the meter, and actual airmass interpolated from measured sample. The AFM is located in the lid of the air filter can, as is the air temperature sensor, a thermistor type sensor. The combo of air flow and air temp measured yields air mass flowing.

The water temp sensor tells the ecu if the mixture needs to be enriched for proper cold engine mixtures, like a carb choke works. It's another thermistor, two wire sensor on the water neck.

The throttle position sensor tells the ecu the driver's power demand at this instant, and over time, to tell the ecu if driver wants to accelerate (accel needs richer mixtures) or back off (mixture leaned or injectors killed for economy/emissions), or cruise at steady state (ecu goes into closed loop, where O2 sensor signals tell ecu to enrichen or lean the mixture to keep mixtures around 14.7:1 stoichiometric least emissions mixture. The ecu uses air mass as a basic paramater, adds cold enrichment, accel enrichment, and deducts decel lean out, and uses the final sum as injector pulse time from a master lookup table in ROM in the ecu (ROM is the "chip" that carries the permanent operating programs and lookup tables for the ecu). The injectors get 12v+ power all the time, current flow limited by resistors in between power source and injector, and the injector ground is switched by the ecu to make the injector circuit for the lookup pulse time. since the pressure is kept constant at the injector by the fuel pressure regulator, and fuel pressure as regulated is further adjusted by boost pressure (so fuel always has the same pressure drop across the injector valve opening), you only have to regulate pulse time to regulate fuel quantity VERY closely.

One further alteration of fuel pressure is performed by the MAP sensor signal. This is a 2 bar MAP sensor, convering a range of -15psi vacuum to +15psi of boost, and incorporates in pre 86.5 versions a 14psi boost pressure switch. The 14psi switch kills engine spark when triggered as a failsafe for overboosted engines. If the ecu does not see a spark event, it won't pulse the injectors and kills the fuel pump. The ecu uses MAP signals for enrichment when under turbo boost. Engines make best power around 12.0:1 - 13.0:1 mixtures. Low vacuum or high (really any) boost or a fast opening throttle (TPS over time signal) means power is required, and the ecu increases pulse time some more for more fuel to the motor.

The TB has a combo ISC and idle position switch. The isc controls idle throttle opening with a stepper motor to control idle rpm, and uses the idle position switch to tell the ecu driver is off the gas completely, and the ecu consults the vehicle speed sensor to be sure the vehicle isn't stopped, and if not, kills fuel entirely for economy and emissions, and if stopped, uses the ISC to control engine speed.

Turbo boost is limited by a mechanical system. A sealed can with single diaphragm (87 and earlier) or double two stage diaphragm (88-89) and a rod connected to the diaphragm control the opening of the waste gate, a valve that controls the bypass of exhaust gas around the turbo power turbine, limiting boost pressure by applying boost pressure to the diaphragm in oppositon to a calibrated spring. When bosst pressure hits 7.5psi (=<87 and 88-89 first stage), or 10psi (88-89 2nd stage), the pressure overcomes the spring, moves the rod, opens the waste gate valve, and limits power to the turbo. *88-89 a/t cars had up to 10psi in all gears. m/t cars were limited to 7.5psi in lower gears to protect fragile tranny. The StarQuest used the same m/t internals, so be warned.