There are lots of components that can affect the fuel system and cause it to be too lean. Follow this Real Fix to see how a code P1128 on this Hyundai Accent was diagnosed and repaired.
Vehicle
2000 Hyundai Accent GL 1.5L
Title
P1128, Replaced Evap Purge Solenoid Valve
Complaint
The customer state the check engine light is on.
Cause
Connected a scan tool and found code P1128 – Long Term Fuel Trim Multiplicative Too Lean. Used the scan tool to monitor live data and found oxygen sensor (B1-S1) voltage was below 450 mV, indicating a lean condition. Used the scan tool to monitor oxygen sensor (B1-S1) with the engine at idle, induced propane into the intake manifold and found the oxygen sensor (B1-S1) signal responded to the rich condition. Connected a fuel pressure gauge to the fuel rail, tested fuel pressure with the key on and engine off, and found the measured fuel pressure was within the specified range of approximately 49.8 PSI. Connected a smoke machine to the intake manifold and induced smoke into the air intake system to check for leaks, but found none. Used the scan tool to monitor live data, used a pair of pinch pliers to block the evaporative emission (EVAP) hose between the intake manifold and EVAP purge solenoid valve and observed the short term fuel trim (Bank 1) parameter began to decrease, indicating a leaking EVAP purge solenoid valve. Attached a vacuum pump to the EVAP purge solenoid valve and tested the valve by applying vacuum. The EVAP purge solenoid valve leaked and did not retain the applied vacuum, which verified the valve was defective.
Correction
Replaced the EVAP purge solenoid valve, cleared codes, performed a road test and verified the vehicle operated properly. The check engine light did not illuminate and no fault codes returned.