Car feeling weak and sluggish

Not enough fuel flow into the combustion chamber is one of the most common reason why car feel sluggish and weak. This is usually related to fuel system failure such as 

1. Clogged fuel injectors
2. Weak fuel injectors
3. Weak fuel pump
4. Clogged fuel pump filters
5. Clogged fuel filters
6. Clogged fuel line
7. Clogged charcoal canister
8. Faulty fuel pump

Another reason is not enough air flow which cause by

1. Clogged air filter

The 3rd reasons are

1. Bad / faulty spark plugs
2. Bad / faulty spark plugs wiring
3. Bad / faulty ignition coils
4. Bad / faulty spark plug cables

There are fundamental factors in combustions which is fuel, air (oxygen), fire (spark plugs). If any of these are faulty or worn out it will affect the car performance.

Fuel Consumptions in Electronic Fuel Injection (EFI) engine system Perodua Alza

Cold Engine

1. Coolant Temperature Sensor - as the coolant sensor detected low temperature it will increase RPM on idle around 1200 ~ 1500 RPM and reduce to 750 ~ 850 when the sensor detected it already reaches optimum temperature around 80 ~ 85 degree celcius for sedan car. At higher RPM it consumes more fuel as injectors and spark plug pulse command more activities by the ECU based on the coolant temperature

Acceleration

1. As car accelerates (more gas pedal is being press) the throttle body sensor send signal to the ECU based on the sensor data which detected the percentage opening of the butterfly cover of the throttle body. More opening leads to more air intake thus ECU will deliver signal to injectors to spit out more fuel fuels based on 14.7 : 1 fixed stoichiometry benchmark.
2. Besides there are air flow sensor, oxygen sensors, and camshaft sensor data also determine the fuel injections by the ECU command.

It is possible sensors data may delay its delivery to ECU and also possible the ECU is delay in processing the data and delay delivery. Potential root causes

1. Frayed wiring - torn or frayed or damaged wiring could slowdown delivery of electrical signals
2. Excessive engine bay heat - excessive heat within the engine bay increase resistant in all the cable affected within the engine bay thus slowing down electrical signals
3. Bad ground - due to rust and aging deteriorating ground cable thus increase resistant to the ground connections. This will affect all the sensors to deliver delay data.
4. Aging sensors - becoming less effective in gathering data i.e. o2 sensor, camshaft sensor, coolant sensor and deliver to ecu. As a result ECU will deliver wrong command signal to the spark plugs and fuel injectors.
5. Aging alternators - deliver less effective electric current to the battery and all the electronic systems.
6. Worn / loose serpentine belt reduce the effectiveness of alternators
7. Worn-out batteries - reduce the effectiveness to deliver enough current to electrical system of the car

The root causes of cars' poor fuel economy or high fuel consumptions

When we think of cars' fuel consumptions usually we ought to relate it to the spark plugs, fuel pump, fuel injectors, oxygen sensors, map sensors, maf sensors, catalytic converter, or engine wear and tears. These many different factors have made us forget about what driven the fuel consumptions in most engine and that is including cars, generators, motorbikes, etc and that is the gas pedal and loads in needs to overcome. 

Most of us overlook what actually driven the engine to consume more fuels because the gas pedal is press more frequently especially in city driving. And of course you have to press even more when the load of the car is heavier or weaker in order to move the car at the pace you want.