Podcast
Questions and Answers
A scan tool is used in diagnosis to observe ________.
A scan tool is used in diagnosis to observe ________.
- Short term fuel trim
- Idle air counts
- All of these (correct)
- Long term fuel trim
All of the following statements are correct EXCEPT ________.
All of the following statements are correct EXCEPT ________.
- Lower than specified injector resistance means the injector is shorted
- Fuel injectors on a gang fire system are wired in series (correct)
- None of these
- The resistance of a group of injectors that fire at the same time can be tested together
All of these are types of injector circuits EXCEPT ________.
All of these are types of injector circuits EXCEPT ________.
- Peak and hold
- All of these are types of injector circuits (correct)
- Pulse width modulated
- Saturated switch
An injection cleaning machine is being discussed. Technician A says that the applied pressure should be between 75-90 PSI before starting the engine. Technician B says to pressure clean the fuel system using a 2:1 mixture of solvent to gasoline. Which technician is correct?
An injection cleaning machine is being discussed. Technician A says that the applied pressure should be between 75-90 PSI before starting the engine. Technician B says to pressure clean the fuel system using a 2:1 mixture of solvent to gasoline. Which technician is correct?
During a fuel injector pressure drop test, the difference between any two fuel injectors should not exceed ________.
During a fuel injector pressure drop test, the difference between any two fuel injectors should not exceed ________.
Fuel injection service is being discussed. Technician A says that the throttle plate(s) should be cleaned. Technician B says that the fuel rail should be cleaned. Which technician is correct?
Fuel injection service is being discussed. Technician A says that the throttle plate(s) should be cleaned. Technician B says that the fuel rail should be cleaned. Which technician is correct?
Fuel injectors can be tested using ________.
Fuel injectors can be tested using ________.
How much voltage is generally available to fuel injectors (most vehicles)?
How much voltage is generally available to fuel injectors (most vehicles)?
If the throttle plate needs to be cleaned, what symptoms will be present regarding the operation of the engine?
If the throttle plate needs to be cleaned, what symptoms will be present regarding the operation of the engine?
In a typical port fuel injection system, which injectors are most subject to becoming restricted?
In a typical port fuel injection system, which injectors are most subject to becoming restricted?
Most port fuel-injected engines operate on how much fuel pressure?
Most port fuel-injected engines operate on how much fuel pressure?
On a vehicle with a mass airflow injection system, which of the following is likely to occur with a vacuum leak at idle?
On a vehicle with a mass airflow injection system, which of the following is likely to occur with a vacuum leak at idle?
On a vehicle with a speed density fuel injection system, which of the following is likely to occur with a vacuum leak?
On a vehicle with a speed density fuel injection system, which of the following is likely to occur with a vacuum leak?
Port fuel-injection systems generally use what type of injector driver?
Port fuel-injection systems generally use what type of injector driver?
Technician A always uses a special service tool to pulse fuel injectors. Technician B says that the injector for each cylinder should only be flow tested four times without starting the engine. Which technician is correct?
Technician A always uses a special service tool to pulse fuel injectors. Technician B says that the injector for each cylinder should only be flow tested four times without starting the engine. Which technician is correct?
Technician A says that all the fuel injectors on an engine should have the same electrical resistance. Technician B says that the difference between any two injectors should be less than 2 ohms. Which technician is correct?
Technician A says that all the fuel injectors on an engine should have the same electrical resistance. Technician B says that the difference between any two injectors should be less than 2 ohms. Which technician is correct?
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Study Notes
Fuel-Injection Diagnosis Overview
- A scan tool aids diagnosis by observing parameters like idle air counts, long-term fuel trim, and short-term fuel trim.
- In a gang fire system, fuel injectors are wired in parallel, not series.
Injector Circuits and Testing
- Types of injector circuits include saturated switch, pulse-width modulated, and peak and hold.
- Fuel injectors can be tested using an oscilloscope, an ohmmeter, or a stethoscope.
Maintenance and Cleaning
- An injection cleaning machine requires 75-90 PSI before engine start; proper cleaning solutions should be mixed at 2:1 solvent to gasoline.
- Both the throttle plates and fuel rails should be cleaned during fuel injection service.
Fuel Injector Performance
- During a pressure drop test, the difference in pressure between any two injectors should not exceed 1.5 PSI.
- Port fuel-injected engines typically operate at fuel pressures of 35 to 45 psi (240 to 310 kPa).
- For a vehicle with a mass airflow injection system, a vacuum leak at idle leads to a lean fuel mixture.
Effects of Vacuum Leaks
- On a speed density injection system, a vacuum leak can result in increased calculated load, increased idle speed, and increased MAP sensor voltage.
Injector Driver and Resistance
- Port fuel-injection systems generally utilize a saturated switch for injector driver.
- All fuel injectors on an engine should have the same electrical resistance, with differences between any two injectors remaining below 2 ohms.
Fuel Injector Flow Testing
- Special service tools are required to pulse fuel injectors; each injector should be flow tested multiple times without starting the engine.
Common Engine Symptoms
- Symptoms of a dirty throttle plate include rough idle, stalling, and hesitation on acceleration.
- Injectors at the end of the fuel rail or bends in the rail are more prone to restriction due to fuel flow dynamics.
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