Nobody wants to spend more on gas than they need to. Lots of things can cause your fuel economy to decrease and without any codes, you have to hunt around for the problem. Follow this Real Fix to see how a poor fuel economy complaint on this Chevrolet Impala was diagnosed and corrected.
Vehicle
2003 Chevrolet Impala Base 3.4L
Title
Vehicle Has Poor Fuel Economy, Replaced Fuel Pressure Regulator
Complaint
The customer states the vehicle has poor fuel economy.
Cause
Connected a scan tool to check for codes and found no codes were present. With the engine running, used the scan tool to monitor live data and observed the oxygen sensor voltage indicate a rich air fuel mixture condition. Further monitoring of the engine data showed the long term fuel trim was a negative percentage, which confirmed a rich air fuel condition. Used the scan tool to monitor the throttle position sensor, engine coolant temperature sensor and the mass airflow sensor, and observed no abnormal readings. Performed an inspection of the air filter and found it was clean. Key off, attached a fuel pressure gauge to the fuel pressure test port, started the engine, and observed the fuel pressure was above the specified range. Removed the fuel pressure regulator vacuum hose and found fuel was present in the hose. The results of these tests verified the fuel pressure regulator was faulty. Connected a scan tool to check for codes and found no codes were present. With the engine running, used the scan tool to monitor live data and observed the oxygen sensor voltage indicate a rich air fuel mixture condition. Further monitoring of the engine data showed the long term fuel trim was a negative percentage, which confirmed a rich air fuel condition. Used the scan tool to monitor the throttle position sensor, engine coolant temperature sensor and the mass airflow sensor, and observed no abnormal readings. Performed an inspection of the air filter and found it was clean. Key off, attached a fuel pressure gauge to the fuel pressure test port, started the engine, and observed the fuel pressure was above the specified range. Removed the fuel pressure regulator vacuum hose and found fuel was present in the hose. The results of these tests verified the fuel pressure regulator was faulty.
Correction
Replaced the fuel pressure regulator and verified the vehicle operated properly. The customer’s concern did not return.
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