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Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 35843
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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1999 crown vic Failed emission test.P0303

Resolved Question:

1999 crown vic Failed emission test.P0303
Submitted: 6 years ago.
Category: Ford
Expert:  Ron replied 6 years ago.
Hello and Welcome to Justanswer,

My name is XXXXX XXXXX I am here to try and assist your with your question.

The code P0303 is set due to an engine miss on the #3 cylinder (3rd one back drivers side) and in most cases this miss is set due to a bad spark plug and or the spark plug boot. In some cases it can also be the coil. I would start with swapping #2 and #3 coils and see if the miss moves. If it does, replace the coil and boot, if it dosnt, replace the #3 spark plug.
Customer: replied 6 years ago.

thanks for the tip on misfire

what about the evap code P0455 emission contol sys leak what is the best way going about identifying where leak is located

Expert:  Ron replied 6 years ago.

The code P0455 is set by any of the following .

P0455 - EVAP Control System Leak Detected (No Purge Flow or Large Leak)The PCM monitors the complete EVAP control system for no purge flow, the presence of a large fuel vapor leak or multiple small fuel vapor leaks. The system failure occurs when no purge flow (attributed to fuel vapor blockages or restrictions), a large fuel vapor leak or multiple fuel vapor leaks are detected by the EVAP running loss monitor test with the engine running (but not at idle).
  • After-market EVAP hardware (such as fuel filler cap) non-conforming to required specifications
  • Disconnected or cracked fuel EVAP canister tube, EVAP canister purge outlet tube or EVAP return tube
  • EVAP canister purge valve stuck closed
  • Damaged EVAP canister
  • Damaged or missing fuel filler cap
  • Insufficient fuel filler cap installation
  • Loose fuel vapor hose/tube connections to EVAP system components
  • Blockages or restrictions in fuel vapor hoses/tubes (items also listed under disconnections or cracks)
  • Fuel vapor control valve tube assembly or fuel vapor vent valve assembly blocked
  • Canister vent (CV) solenoid stuck open
  • Mechanically inoperative fuel tank pressure (FTP) sensor
Check for audible vacuum noise or significant fuel odor in the engine compartment or near the EVAP canister and fuel tank.
Ron and 3 other Ford Specialists are ready to help you
Expert:  Ron replied 6 years ago.
I can send you the pinpoint test if you need it.