Question135,000, owned from new and babied! All services, 3000 mile oil changes.Consistent 30 plus mpg, rain or shine, in or out of traffic. Last April SUDDEN drop from one fill to the next to a STEADY 20mpg (I check every fill by zeroing the trip) - FOrd dealer kept car for 2 days, replaced MAF sensor and PCV hose. Still doing 20 mpg. Went back - another 2 days - found wrong engine coolant temp sending unit, replaced ECT and decarb intake valves, fuel injection peformance flush. test and clean injectors, clean throttle body, 4 cylinder mini tune, replaced platinum plugs. Car came back running like a dream. Spent $1000 so far - STILL doing steady 20 mpg!! They took it back for another 2 days - found HEGO a little slow. Took car to another Ford dealer nearer home with full history. They replaced Oxygen Sensor. engine light systems check, Tested EEC system for codes all pass codes 111 10 111. Checked EEC parameters, fuel trims - normal, external components, cooling system 197 F Good. No engine related faults. Pronounced the car in excellent condition - spent another $400. Car running like a dream - STILL doing a steady 20 mpg. I changed to Chevron - added Techron - no change. Can you help please Dennis????????
AnswerIs the engine reaching normal temperature? One of the biggest problems on these was the thermostat opening too soon. This will hardly ever set a PCM code. Where on the temp guage is the engine in normal driving? Should be near the middle of guage.
Did the shop check fuel pressure, leakdown, injector flow, vacuum leaks, fuel leaks?
Are there any new drivers of this vehicle, kids, grandkids, etc. Have your driving habits changed, or driving routes changed? Are the brakes dragging? I doubt some of these items will cause a sudden drop in mileage, but these are questions I would ask if you came to my shop. Can your calculations be off for any reason? Speedometer change recently, or something affecting the odometer readings?
I can't think of anything typical to this vehicle to cause the mileage change, but I wouldn't spend any more money until someone has a definitive answer. I believe these shops were selling you parts in an attempt to placate your desire for better mileage. An HEGO a little slow will not cause what you describe. If the engine runs right, you may have to lay off the fuel mileage for a while, and not focus on that so much as how it runs.
Yes, I know the price of fuel. I would suggest thinking about how you calculate fuel mileage, see if there are any discrepancies. Instead of using the odometer compared to fuel used, see how many miles you can get per tankful. Is there any damage to the fuel tank that would affect the guage readings? Different tires recently?
Please follow up and let me know what turns up, if anything.
