General Troubleshooting Guidelines (Digifant II)
DIGIFANT IIFuel Systems can be repaired by following the step-by-step procedures shown.
Make Sure You Understand The Customer's Complaint
- Identify the symptoms as you follow the diagnosis procedure. Try to determine the cause of the problem.
- Repair the problem after you have identified the symptoms.
- After completing repairs, always road test the vehicle before returning it to the customer.
Preliminary Checks
A complaint may be caused by a minor detail. Before starting the fault finding procedure, make a few visual checks, such as:
- Are all electrical connections clean and tight? Spark plug wires not hanging loose, etc.
- Are all hoses OK? Check vacuum, crankcase ventilation, fuel tank ventilation, and air intake hoses for restrictions, cracks, or looseness.
- Are all the ground connections OK?
- Is there adequate fuel supply?
Pinpointing The Problem
Remember the basics:
- No matter how advanced the system, to start and run an engine you need correct spark timing, and the proper fuel-to-air ratio.
- Get as much information as possible from the customer.
- Gather as many symptoms as possible.
- Check the simple things first.
^ Look for spark.
^ Listen for the fuel pump.
^ Feel the injectors operating.
- Make logical deductions, not assumptions.
Intermittent Engine Performance Complaints
Intermittent performance complaints can be caused by any part of the electrical, ignition, or fuel systems. Therefore, obtain as much information as possible from the customer. Find out under what conditions the problem occurs, how often, and for what duration. For example: engine cold?, during warm-up?, under load?, light acceleration?, highway driving?, only in hot weather?, only at high altitude?, etc.... If possible, road test the vehicle to duplicate the condition.
When troubleshooting intermittent engine performance complaints:
- Pay very close attention to electrical connections on the fuel injection harness. Connectors which have insufficient tension, are bent, or show signs of corrosion should be replaced and not repaired.
- Corroded and/or loose ground connections should be cleaned and tightened.
- The complete fuel system should be checked, including the fuel quality.
Engine will not start, hot or cold
A. No Fuel
- Fuel System (Circuit Tests)
- Injectors (Circuit Tests)
- Air Flow Sensor
B. No spark
- Ignition System
Hard starting, hot or cold
A. Insufficient or excessive fuel
- Coolant Temperature Sensor
- Fuel System
- Residual Pressure Test
- Evaporative Emission System
B. Weak or no spark
- Ignition System
Poor idle
A. At operating temperature
- Throttle Switch
- Idle Stabilization System
- Evaporative Emission System
- Intake Air Preheating
B. Cold engine
- Coolant Temperature Sensor
- Idle Stabilization System
- Intake Air Preheating
Engine stalls at highway speeds
A.
- Fuel System (Pressure, Volume, Current Draw)
- Evaporative Emission System
- Basic Engine Adjustments
- Ground and Terminal Connections
Poor performance
A. During warm-up
- Basic Engine Adjustments
- Coolant Temperature Sensor
- Throttle Switch
- Idle Stabilization System
- Intake Air Preheating
B. At operating temperature
- Basic Engine Adjustments
- Throttle Switch
- Knock Sensor
- Oxygen Sensor System
- Ignition System
- Fuel System (Pressure, Volume, Current Draw)
- Idle Stabilization System
- Intake Air Preheating
C. At full throttle
- Full Throttle Enrichment
- Knock Sensor
- Ignition System
High fuel consumption
- Oxygen Sensor System
- Fuel System (Pressure, Volume Tests)
- Fuel Injectors (Spray Pattern, Leakage)
- Full Throttle Enrichment
- Evaporative Emission System (Leakage)
Note:
Driveability problems that occur even when all engine specifications are in order may be caused by injector tip gum-up or carbon build-up on the intake valves and injector tips. These deposits are related to the use of gasoline with insufficient cleaning additives and can be prevented by:
- Using only major brand gasoline that advertise their additive packages are effective for cleaning fuel injection systems.
- Avoiding fuels that contain alcohol.
- Regular use of supplemental additives such as Autobahn Fuel Additive, which is specially formulated to prevent carbon, gum or varnish build-up and help break down existing deposits.
Once formed, many deposits cannot be removed by normal preventative measures such as the use of fuel additives. Most injector deposits can be removed by using a special cleaning system like our C-16 Fuel Injection System Cleaner. Carbon build-up may require mechanical removal.
Check Croup 24 of your Technical Information Book for further information on injection system cleaning and de-carbonization.