Hotwire 450SE - Non start with AFM then high idle
Discussion
This might help :
''Airflow Meter
This is one of the key fuel-metering elements of the system. Note that you can drive without an airflow meter in case of emergency (i.e. airflow meter disconnected), because the system will drop into a default (limp-home) mode based on throttle opening.
Most airflow meter faults will cause the engine to run excessively rich. However if the airflow meter remains connected whilst defective then the vehicle will probably not run. In most cases the output from a defective airflow meter will be in the range 2.0-2.5 Volts, which is a viable value. This represents a moderate load and will cause heavy over-fuelling without setting a fault code.
Testing is performed in the following manner. Peel back the rubber boot on the airflow meter connector and leave it plugged in to the airflow meter. Set up the digital multimeter to read voltage. Insert the negative probe into the Red/Black wire (sensor ground), and the positive into the Blue/Green wire (Airflow signal).
Turn on the ignition, but do not start the engine. The meter should immediately indicate a reading of approximately 0.3-0.34 Volts. Most defective airflow meters will overshoot to 0.5 Volts or higher, and take at least 2 seconds to come down to the correct voltage.
Now start the engine, and the reading should rise to 1.6 Volts (3.5 Litre engine) to 1.75 Volts (5.0 Litre engine).
The next test is full load, and as with the fuel pressure test it will require use of a rolling road or a steep hill in the same manner. Under full load the voltage should rise to 4.45 Volts (3.5 Litre engine) to 4.95 Volts (5.0 Litre engine).
(This should establish is the AFM is shot) but could also indicate wiring issues (snapper or frayed wires.. try wiggling them and is if voltages change).
Coolant and Fuel Temperature Sensors
Both these items are very similar in operation, and can be tested in the same way. Firstly a simple recap on the function of each one. Both of these devices almost always fail open-circuit, and are usually intermittent in the early stages of decline. Whilst they are intermittent they usually play up when hot rather than when cold.
The Coolant Temperature sensor is used to enrich the fuel mixture when the engine is cold. These devices almost always fail open-circuit, which makes the injection system believe that the engine is at somewhere around –40 degrees Centigrade. The system will always detect this as a fault condition, and use a substitute value of 30 degrees Centigrade whilst setting a fault code in the ECU. In practice this means that the car will be difficult to start when cold (too lean), and will be too rich when warmed up. However it will usually get home!
The Fuel Temperature sensor is used to enrich the fuel mixture when the engine is very hot, in order to compensate for decreasing density of the fuel as it approaches boiling point. Failure of this sensor does not produce major symptoms other than slight difficulty with hot starting. The system will always detect this as a fault condition, and use a substitute value of 30 degrees Centigrade whilst setting a fault code in the ECU. Historically, these Fuel Temperature sensors have proved to be very reliable.
A very simple resistance test will give a good indication of the health of the sensor. Disconnect the sensor, and probe it with the multimeter set to measure resistance. The resistance should be approximately 2400-2600 Ohms at 20 degrees Centigrade, and 300-400 Ohms at 80 degrees Centigrade.
''Airflow Meter
This is one of the key fuel-metering elements of the system. Note that you can drive without an airflow meter in case of emergency (i.e. airflow meter disconnected), because the system will drop into a default (limp-home) mode based on throttle opening.
Most airflow meter faults will cause the engine to run excessively rich. However if the airflow meter remains connected whilst defective then the vehicle will probably not run. In most cases the output from a defective airflow meter will be in the range 2.0-2.5 Volts, which is a viable value. This represents a moderate load and will cause heavy over-fuelling without setting a fault code.
Testing is performed in the following manner. Peel back the rubber boot on the airflow meter connector and leave it plugged in to the airflow meter. Set up the digital multimeter to read voltage. Insert the negative probe into the Red/Black wire (sensor ground), and the positive into the Blue/Green wire (Airflow signal).
Turn on the ignition, but do not start the engine. The meter should immediately indicate a reading of approximately 0.3-0.34 Volts. Most defective airflow meters will overshoot to 0.5 Volts or higher, and take at least 2 seconds to come down to the correct voltage.
Now start the engine, and the reading should rise to 1.6 Volts (3.5 Litre engine) to 1.75 Volts (5.0 Litre engine).
The next test is full load, and as with the fuel pressure test it will require use of a rolling road or a steep hill in the same manner. Under full load the voltage should rise to 4.45 Volts (3.5 Litre engine) to 4.95 Volts (5.0 Litre engine).
(This should establish is the AFM is shot) but could also indicate wiring issues (snapper or frayed wires.. try wiggling them and is if voltages change).
Coolant and Fuel Temperature Sensors
Both these items are very similar in operation, and can be tested in the same way. Firstly a simple recap on the function of each one. Both of these devices almost always fail open-circuit, and are usually intermittent in the early stages of decline. Whilst they are intermittent they usually play up when hot rather than when cold.
The Coolant Temperature sensor is used to enrich the fuel mixture when the engine is cold. These devices almost always fail open-circuit, which makes the injection system believe that the engine is at somewhere around –40 degrees Centigrade. The system will always detect this as a fault condition, and use a substitute value of 30 degrees Centigrade whilst setting a fault code in the ECU. In practice this means that the car will be difficult to start when cold (too lean), and will be too rich when warmed up. However it will usually get home!
The Fuel Temperature sensor is used to enrich the fuel mixture when the engine is very hot, in order to compensate for decreasing density of the fuel as it approaches boiling point. Failure of this sensor does not produce major symptoms other than slight difficulty with hot starting. The system will always detect this as a fault condition, and use a substitute value of 30 degrees Centigrade whilst setting a fault code in the ECU. Historically, these Fuel Temperature sensors have proved to be very reliable.
A very simple resistance test will give a good indication of the health of the sensor. Disconnect the sensor, and probe it with the multimeter set to measure resistance. The resistance should be approximately 2400-2600 Ohms at 20 degrees Centigrade, and 300-400 Ohms at 80 degrees Centigrade.
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