Sounds like you simply haven't driven your Ford Mustang long enough (or under to right drive cycle parameters) to complete the drive cycle. We recommend completing a few more drive cycles before your next smog test.
Description of Ford OBDII Drive Cycle
The following procedure is directly from Ford and designed to complete the OBDII monitors required to get your Ford Mustang to pass the OBDII Monitors portion of the smog check, also known of the I/M readiness test. The FORD OBDII Drive Cycle should be performed using a scan tool in order to speed up the drive cycle.
Drive Cycle Recommendations:
1.Most OBDII monitors will complete more readily using a "steady foot" driving style during cruise or acceleration modes. Operating the throttle in a "smooth" fashion will minimize the time required for monitor completion.
2. Your Mustang's fuel tank level should be between 1/2 and 3/4 fill with 3/4 fill being the most desirable.
3.The Evaporative Monitor can only operate during the first 30 minutes of engine operation. When executing the procedure for this monitor, stay in part throttle mode and drive in a smooth fashion to minimize "fuel slosh".
Drive Cycle Preparation - 1. Install scan tool. Turn key on with the engine off. Cycle key off, then on. Select appropriate Vehicle & Engine qualifier. Clear all DTC's/ Perform a PCM Reset. Begin to monitor the following PIDs: ECT, EVAPDC, FLI (if available) and TP MODE. Start vehicle WITHOUT returning to Key Off. Idle vehicle for 15 seconds, then drive at 40 MPH until ECT is at least 170°F.
Prep for Monitor Entry - 4. Is IAT within 40 to 100° F? If Not, complete the following steps but, note that step 14 will be required to "bypass" the Evap monitor.
HEGO Monitor - 5. Cruise at 40 MPH for up to 4 minutes.
EVAP Monitor - 6. Cruise at 45 to 65 MPH for 10 minutes (avoid sharp turns and hills) Note: To initiate the monitor TP MODE should =PT, EVAPDC must be >75%, and FLI must be between 15 and 85%
Catalyst Monitor - 7. Drive in stop and go traffic conditions. Include five different constant cruise speeds, ranging from 25 to 45 MPH over a 10 minute period.
EGR Monitor - 8. From a stop, accelerate to 45 MPH at 1/2 to 3/4 throttle. Repeat 3 times.
SEC AIR/CCM (Engine) - 9. Bring the vehicle to a stop. Idle with transmission in drive (neutral for M/T) for 2 minutes.
CCM (Trans) - 10. For M/T, accelerate from 0 to 50 MPH, continue to step 11. For A/T, from a stop and in overdrive, moderately accelerate to 50 MPH and cruise for at least 15 seconds. Stop vehicle and repeat without overdrive to 40 MPH cruising for at least 30 seconds. While at 40 MPH, activate overdrive and accelerate to 50 MPH and cruise for at least 15 seconds. Stop for at least 20 seconds and repeat step 10 five times.
Misfire & Fuel Monitors - 11. From a stop, accelerate to 65 MPH. Decelerate at closed throttle until 40 MPH (no brakes). Repeat this 3 times.
Readiness Check - 12. Access the ON-Board System Readiness (OBDII monitor status) function on the scan tool. Determine whether all non-continuous monitors have completed. If not, go to step 13.
Pending Code Check and Evap Monitor "Bypass" Check - 13. With the scan tool, check for pending codes. Conduct normal repair procedures for any pending code concern. Otherwise, rerun any incomplete monitor. Note: If the EVAP monitor is not complete AND IAT was out of the 40 to 100° F temperature range in step #4, or the altitude is over 8000 ft., the Evap "bypass" procedure must be followed. Proceed to step 14.
Evap Monitor "Bypass" - 14. Park vehicle for a minimum of 8 hours. Repeat steps 2 through 12. DO NOT REPEAT STEP 1.
