Poor gas mileage

Q1:(2000 mercury grand marquis) fuel filter,spark plugs,upstream o2 sensors,new mass air flow sensor,air filter,at fluid and filter change,inflate tire to 38 psi,change diffrential oil.scanned pcm twice and checked for vacum leaks and catalytic converter blockage all fine… there is no brake drag symptoms or backpressure caused by bad cats, all checked fine but my problem is that my gas mileage is horrible I get 180 miles in city and 200 miles highway and 220-230 miles if on a long highway going at 60-75 miles with light foot in either situations and I am sure that the odometer is fine and accurate because most of my driving is highway and I always reset the trip meter when I fill up the tank…the fuel sending unit is okay because it takes 13-14 gallons to fill up I have scanned the vehicle a third time yesterday and made the technicians inspect the vehicle and they could not find any thing… they told me that the fuel vapor canister could be the problem but they are not sure…besides I could not find any thing on the internet that confirm this or that it has any thing to do with gas mileage and by the way my gas mileage have not changed not even 1mpg… please help me It is driving me crazy all I can think of now is the fuel vapor canister and the fuel pressure regulator and the fuel injectors though my car accelerate just fine and has no problems or misfire or any thing that indicates problems and by the way my brother has a 99 crown vic and gets 300 miles till the low fuel light comes on and I gave him my my car to test it and he said that it does accelerates fine just like his car and he felt that my car had better horse power at hard accleration but that is because my car is a dual exhaust with 215 hp and his is single exhaust with 200hp…thanks Q2:Loose steering I will be replacing the whole linkage from the steering wheel to the steering gear box based on http://www.p71interceptor.com/ and it will be 2-3 weeks till I do it… I bought this vehicle 4 months ago with 139000 miles on it and I replaced all the suspension and steering tie rod ends, ball joints, shocks,front coil spring,… The question is does the steering gear detertioate gradually I mean does it contribute to the looseness in the steering… on the the website it is obvious that the steering linkage parts are what make the steering loose but what about the steering gear I mean how to inspect it since it is expensive

SYMPTOM BASED TROUBLESHOOTING is a crapshoot! Unfortunately, for you, that’s what you have been doing. I feel sorry for your customers if you run a shop this way; or, are you just directing the “technicians” in someone else’s shop to change parts for you?

Try some troubleshooting where you test, check, and inspect parts and components for faults BEFORE you change them. WHY you do something can matter more than WHAT you do. Of course, the WHAT matters, also.

First I suggest starting to measure miles per gallon not per fill up. It is much more accurate. When you fill up divide the number of miles since the last fill up and divide by the number of gallons. It really is not that hard. Us a calculator if necessary.

Sorry if I am asking something that you may have already mentioned (I really have a tough time reading all that text that does not appear to have sentences or paragraphs), but how about some history. How many miles on the car, how long have you had it? Has the mileage recently dropped? Is the driver, an aggressive driver?

It sounds like you may have a lot of things going on, but it is hard to tell from what information we have. However as Hello suggested, I suggest more troubleshooting.

Have you confirmed the accuracy of your odometer? Have you confirmed your actual miles per gallon, and not just your miles per tank? Perhaps the problem isn’t fuel economy, but the measurement of fuel economy?

Poor milage + loose steering + suspension parts replaced = bad wheel alignment.

I’ve seen wheel alignment reduce milage by 20%.