Fuel Injection Troubleshooting

Engine Cranks But Does Not Start

  • Ignition bad – check battery, distributor, plugs, coil and timing.
  • Engine defect – compression, oil pressure, valve adjustment.
  • Air intake leak – vacuum leak – check all hoses and connections.
  • Fuel blockage – dirty fuel filter, kinked fuel hose, non injection type hose being used.
  • Relay defection or wiring to injectors.
  • Fuel pump bad – check the fuel pump fuse, pump relay and pressure test pump.
  • Fuel pressure low – check pressure regulator.
  • Cold start valve not working – test for spray, check wiring and thermo time switch.
  • Thermo time switch defective – test resistance readings vs. temperature.
  • Auxiliary air valve not operating correctly – must be open with cold engine, closed with hot engine.
  • Temperature sensor defective
  • Air float meter defective – check pump contacts and test flap for free movement.
  • Loose connection in wiring harness or system ground.
  • Control unit defective.

Engine Starts Then Dies

  • Defective ignition – check plugs, distributor, coil & timing.
  • Defect in engine – compression, valves, oil pressure
  • Vacuum leak – check all hoses and fittings.
  • Fuel system blockage – dirty fuel filter, kinked fuel line, collapsed rubber fuel line.
  • Fuel pressure incorrect – fuel regulator, fuel pump.
  • Cold start valve leaking
  • Auxiliary air valve not operating.
  • Bad temperature sensor
  • Air flow meter
  • Idle speed too low.
  • CO concentration incorrect.
  • Loose connection in wiring harness or ground.
  • Control unit defective.

Hesitates or Runs Rough at Low Speed

Unfortunately like most fuel problems it is hard to pin down a problem with one solution.

  • Mass Airflow Sensor: The mass airflow sensor measures the air entering the engine and sends the data to the car’s computer. A bad mass airflow sensor will usually generate an error code and the check engine light will come on.
  • Fuel Pump: The fuel pump in most vehicles is inside the fuel tank and pumps fuel up to the engine. A weak fuel pump will send less than needed fuel to the engine. If your vehicle is working OK at higher speeds then you can probably rule out the fuel pump.
  • Throttle Position Sensor: A throttle position sensor tells the car’s computer how far the throttle is open and how hard the accelerator is being pressed. The computer is then able to adjust the fuel/air mixture going to the engine so that is stays at the correct level. If the throttle position sensor is not working properly, it may be sending incorrect information to the vehicle’s computer. The computer may then not provide the engine with the correct amount of air while accelerating, causing a hesitation sensation.
  • Dirty/Failing Fuel Injectors: Fuel injectors spray fuel in a fine mist into the cylinder where it is mixed with air and ignited by a spark plug. Fuel injectors may become dirty over time and not be able to provide as much fuel to the cylinder as is needed. Dirty fuel injectors may cause the engine to run lean which will in turn, cause hesitation when accelerating.

Gas Smell

If you get a gassy smell it may be the injectors leaking. Check your oil and smell the oil to see if gas is running into the crankcase.

Throttle Position Sensor
Fuel Injectors
Fuel Injector Repair Kits
Updated on 04/13/2022

Was this article helpful?

Related Articles

Need Support?
Can't find the answer you're looking for?
Contact Support