This is a sample of what all Gadgetmen, and the customers that allow this, can expect.
Dec 28, 2010 I got a call at about 8:30 from A Better Cab Service. They were in a panic, as it was the last day for them to get their Crown Vic (Called "Vickie) to pass emission. "Catalytic Converter below efficiency, bank one" is one of the many fault codes that will cause an automatic failure.
They were about to lose their license on this vehicle for at least 30 days, severly impacting their income, as they have only two vehicles in the fleet. So, they wanted my help.
I performed the modification (they made it to the illustrious "Zero List") and the owner was delighted when it "sailed through" the emissions testing process. A week later, he called me and reported Vickie had never run so strong, so clean OR so cheap, now at over 21 mpg's. This was a very respectable increase in mileage of 50%.
About two weeks later, I received another call saying the check engine light was on. Six months later (today) they FINALLY bring the car back to me.
Turns out they had some back-yard mechanic work on it, in the process undoing the vacuum system modification that is so critical to the success of this mod. The result was an enduring check engine light (since they didn't replace the catalytic converter-there was no need after The Groove) and a decrease in mileage to 16 mpg's.
Of course, I redid the vacuum system and added a little "bonus" of reducing the idle air delivery port size from a solid 3/4" to about 3/16" and they were (once again!) on the Zero List.
I'll follow this up with a mileage report when I get one.
If a customer comes back weeks after the mod with no gains, ALWAYS check your work! Remember that most mechanics are nothing more than parts replacers and couldn't care less about what's best for the vehicle!