Ford Repair: Failed evaporative system pressure test, fuel filler cap, mercury sable

Question
QUESTION: Hi Dennis and thank you for your generosity in sharing your knowledge with the world.  I have a 1993 Mercury Sable that failed the evaporative system pressure test.  All else passed with HC at .59, CO at 3.61, and Nox at 1.24 (in case these results affect your diagnosis of the evap system pressure test failure).  I have been unable to find any online diagrams of what may have caused the failure or even an underhood parts location diagram for this car.  What would you suggest I start with?  Thank you in advance for your help.

Sheryl

ANSWER: I would start by checking for codes. Diagnosing an EVAP failure can be challenging for a pro, taking one on at home seems daunting. You did not mention which engine, but regardless, there is a vaccum hose that is a common failure on your car. It connects to a metal pipe top left of engine, in the PCV line, and goes to the EVAP solenoid down below the air cleaner housing. This hose has a tendency to collapse, or split and leak. Did the test fail the cap, or the system? Many EVAP failures a simply a leaking fuel filler cap.

Good luck

---------- FOLLOW-UP ----------

QUESTION: Dennis, Thank you for such a prompt response to my question.  Since the local auto parts store said they were unable to test the codes on the car, I proceeded with your advice to check the vaccumn hose you mentioned and, yes, it did need replacing.  Having done that and also replacing other loose hoses, I would like to reset the code reader.  Could you please give me the procedure to clear the codes and to retest the system. (I have done this before on my 1989 GMC Sierra pickup and was thrilled with the simplicity of it.)  You are wonderful for helping people like me who cannot afford shop repairs.  Thank you from my heart.

Sheryl

Answer
Typically to clear the codes a scanner is used. They can also be cleared by disconnecting the battery for five minutes, in most cases. Retesting for codes requires a scanner, or a procedure with a voltmeter that is too involved for me to relate in this forum. I don't know of any test equipment like a scanner/code reader that will run that EVAP test. Most newer vehicles may have that test available, but not in the early nineties models. You may have to run it thru the emissions test again to find out if it's fixed. The other option is to have a shop run a smoke test on the system, where inert smoke is pumped into the EVAP system at low pressure to find any leaks.