Mechanics

UNSOLVED HORRIBLE GAS MILEAGE MYSTERY

2000 Mercury Marquis

2000 Mercury Marquis V8 Two Wheel Drive Automatic 146000 miles

(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



Optional Information:
2000 GRAND MARQUIS LS (HPP) 4.6

Already Tried:
I MENTIONED EARLIER. EXCEPT FOR FUEL PRESSURE REGULATOT, FUEL VAPOR CANISTER I SEARCHED EVERY WEB AND PAGE ON THE INTERNET FOR MORE THAN 4 MONTHS ALL THE THINGS THAT AFFECT GAS MILAGE HAVE BEEN REPLACED
WITH OE PARTS STARTING WITH : 1-FUEL FILTER 2-FUEL INJECTOR CLEANER AND ONE MONTH LATER CLEAN THEM AT A SHOP COST ME 40$. 3-NEW MASS AIR FLOW SENSOR SINCE THE OLD ONE I BROKE ONE OF ITS SCREWS THAT WAS RUSTY I DECIDED TO GET A NEW ONE. (NOTE: EVERYTIME I DISCONNECT THE NEGATIVE CABLE FOR MORE THAN HALF AN HOUR BESIDES PUMBING THE BRAKE PEDAL)
4-REPLACED BOTH THE UPSTREAM O2 SENSORS WITH OEM MOTORCRAFT DY1040.

THE CAR ACCELERATES JUST LIKE A BUTTERFLY SO I DO NOT THINK THERE IS SOMETHING WRONG WITH THE FUEL SYSTEM OR EXHAUST SYSTEM.

THE CAR IS RUSTY BUT THE ENGINE USE A LITTLE OIL EVERY 3000 MILES.I CHECH THE OIL LEVEL EVERY 2 WEEKS

I USE REGULAR GAS AND HAVE BEEN DRIVING WITH A LIGHT FOOT AS I CAN BUT WITH NO LOCK THE CAR ONLY GETS IN THE 15 MPG RANGE.3 WEEKS AGO I FILLED THE TANK WHEN I WAS TRAVELLIN AND RESET ODOMETER AND I DELIBRATLEY DID NOT EXCEED 80MPH AND THE I GOT LIKE 240 MILES ON A FULL TANK.

THE ALIGNMENT IS OKAY. THE GET UP AND GO FINE COMPARED TO MY BROTHER'S CAR.

PLEASE HELP ME AND TELL ME WHERE TO START.
I TALKED TO ONE OF THE BEST TECHNICINAS AND HE SAIS THAT ALL THEY CAN DO IS REPROGRAMM THE PCM OR UPDATE IT (SOMETHING LIKE THAT) BUT HE DID NOT ASSURE THAT IT WILL SOLVE THE PROBLEM.

I AM NOT THE ORIGINAL OWNER. BESIDES I DO NOT THINK THE FAN IS THE CULPRIT SINCE MOST OF MY DRIVING IS HIGHWAY AND MY VEHICLE NEVER EVER OVERHEATED. REGARDING THE A/C I ALWAYS USE THE MAX A/C.
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2000marquis
October 2, 2008.



First the dual exhaust 215 HP engine requires premium gas! Check that regulator, if any gas is in the vacuum line, replace it. A weak regulator may or may not cause driveablity issues until the diaphram breaks! Return line to the tank may be clogged as well!
http://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm
Go here and checkout our video.
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Merlin2021
Oct 2, 2008.


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