Electronic Fuel Injection Final Study Guide
ISC (idle speed control)
- PCM uses inputs to determine the idle speed - a dirty passage can cause low idle speeds
fuel injectors
- are an electrical mechanical device - controlled all at once, in pairs or groups, or sequentially - have a two wire connector - have battery voltage run to injector and are ground side controlled - a dirty injector can cause a misfire and acceleration stumbles
fuel system testing
- do a visual inspection first including vacuum lines, PCV system, and engine coolant level - vacuum leaks, stuck AC switch, and a defective coolant sensor can cause a high idle speed - low fuel pressure will cause a lean condition - defective coolant sensor can cause a rich condition - use a noid light to test for signal to injector
GDI (gas direct injection)
- fuel air ratios can be up to 60 to 1 - can use higher compression ratios - injector is located in the combustion chamber
SFI (sequential fuel injection)
- injector is pulsed just before the intake valve opens - one injector per cylinder located in intake manifold ports - the CMP (cam position sensor) determines #1 cylinder and synchronizes injector firing - the system uses less fuel and produces more power because the fuel is delivered with more accuracy
fuel trim
- is the adjustment of fuel for various engine conditions - can be looked at using a scan tool for diagnostics
throttle body
- is used to control air flow into the engine to control engine speed - houses the TP (throttle position) sensor, IAC (intake air control) actuator, and the throttle plates
TP (throttle position) sensor
- is used to monitor throttle position - sudden opening will cause an enrichment to prevent hesitation - when held fully open puts the system in clear flood mode
fuel pressure loss on shut down
- leaking fuel injector - leaking fuel pump check valve - leaking fuel pressure regulator, fuel will be in the vacuum line - symptom will be hard starting or long crank times
O2 (oxygen) sensor
- measures O2 in the exhaust stream - pre OBD-II use one in the exhaust stream - post OBD-II use one before the catalyst converter and one after - post OBD-II sensors have a heating element to speed the sensor to operation temperature, they use 4 wires - operation is checked with a volt meter or lab scope
MAP (manifold absolute pressure) sensor
- measures pressure in the intake manifold - voltage goes low if vacuum is high
MAF (mass air flow) sensor
- measures the volume of air by weight entering the engine - uses a heated wire that is cooled by the incoming air to measure the volume - hot film GM meters can be tested by tapping on them - meters can be tested by unplugging and driving to see if issues go away
diesel fuel systems
- use many of the same sensors to meet OBD standards - common rail systems can have very high pressures from 2000 - 25000 psi
APP (accelerator pedal sensor)
- used on vehicles that use throttle by wire
CMFI (central multiport fuel injection)
- uses a main injector that is connected with hoses to poppet nozzles located in intake ports which are opened when fuel pressure rises
open loop
- uses a predetermined map to determine pulse width of injectors - block learn and integer or long-term fuel trim and short term fuel trim use a number system of 0 to 255 add or subtract fuel to adjust the fuel air ratio - when a lean condition is detected by the O2 sensor the short term fuel trim will go up then the long term fuel trim will adjust up to bring the short term trim back to 0
PFI (port fuel injection)
- uses one injector for each cylinder
closed loop
- uses the primarally the O2 sensor along with other sensors to adjust the pulse width of injectors
clear flood mode
- when the fuel air mixture is leaned to clear a flooded condition, accelerator is held to wide open position while cranking engine
