My mileage has dropped off significantly and I was going to change the O2 sensor. the haynes manual I have tells me there are 4 but when I talked to Ford they only quoted me for one. they got the information from my VIN number. was this a mistake on there part? should I be changing all 4?

 

First, I'm guessing you have a V6? In the V6 and probably the 4cyl also, there's a pre-cat o2 sensor and one after the cat converter. So if you have a v6 there are 4. If you have a 4cyl there are two.


Before you waste money on the sensors, you should make sure that they're the problem. The computer WILL throw a code if they're not working correctly. It'll also throw a code if they're working properly but the heating element stops working. Any auto parts store should be able to read the code(s) for you... that is, if you have a check engine light on. No light, no code and the o2's are good.


IMO,
Jason

 

ok thanks. so what would have caused my mileage to drop off? I am planning on changing my spark plugs, been waiting till I have enough time to change all of them.

 

What year and configuration is your Escape/Mariner/Tribute (2wd, 4wd)? Are there any drive-ability issues that you've noticed? Any odd behavior or noises?

 

07 escape 3 litre v6 xlt 4wd. everything is normal with the vehicle. it has new tires and is serviced regularly

 

OK, thanks for the info. I should have also asked you if the mileage drop is significant and whether it began suddenly or has been getting worse as time goes on. Also, what is the mileage on the vehicle? That bit of info would help a little in diagnosing your problem.

From my experience and research into these engines and transmissions, here are a few things that could be the cause of poor gas mileage (yet not necessarily set a check engine light on). Not knowing the miles on your vehicle, the below conditions are not in any certain order.

#1 Severely clogged air filter

#2 Engine Coolant Temperature (ECT) Sensor:
The ECT sensor detects the engine coolant temperature and sends this information to the PCM (computer). The PCM uses the ECT sensor to control the operation of the torque converter lock-up clutch (TCC).

Symptoms: The torque converter will never lock-up if ECT sensor reads colder than normal, resulting in reduced fuel economy. Also, the computer uses the ECT sensor values (among other things) to determine air/fuel ratios. Here's an extremely simplified version of how it could effect your mileage. When starting the vehicle when not at operating temperature, the ECT tells the computer the engine is cold. A cold engine needs more fuel and the computer compensates based on the values from the ECT, acting like a 'choke', say on a carbureted vehicle, lawnmower, etc. A failed or failing ECT would send the wrong values to the computer, making it believe the engine has not yet warmed up.

#3 Thermostat:
A thermostat that is stuck open would not allow the engine to achieve optimum operating temperature, or take an abnormal amount of time to achieve that temp. Refer to #2 as to why this would decrease fuel economy. If you've noticed that it takes an abnormally long time for your heater to work or that it never gets very warm, then this is likely your issue.

#4 Spark Plugs:
These vehicles use platinum tipped spark plugs that (according to Ford and all Fords documentation) do not need to be replaced until the vehicle reaches 100,000 miles. Its been my experience that conditions such as #1, 2 and 3 above causes the engine to run overly rich, fuel fouling the plugs. As well, if the vehicle is VERY often driven short distances, it may never warm up adequately and can also foul the plugs. It wouldn't hurt to pull one and check its condition. If the ceramic tip is black/sooty then I'd look into replacing them. Fuel fouled spark plugs often cause a slight rough idle not detectable inside the car, but SEEM to operate normally under partial or full throttle.


There's a few places to start... Also note that any or all of the above conditions cause the computer to inject more fuel than is required. Over time, if not corrected, can clog catalytic converters and foul o2 sensors.

 

I would add to the excellent description made by BluPastU that the air filter is often overlooked, along with tire pressure. It would not hurt to make it a monthly practice to check air pressure in all the tires. The O2 sensors provide a signal used to 'trim' the mixture, and the system will make a pretty good estimate without their input. I would not expect a large increase in fuel consumption if they were inoperative or 'lazy', but there would be some as the sensor sends multiple readings per second as the exhaust gas passes by.
tom

Never mind about the air filter... was already mentioned.
t

 

tire pressure is good and so is the air filter. I have 126000 KM's on it. it seems to warm up fine, doesn't warm up any quicker or slower than normal. I did have a bearing go in my front left side. it set off the ABS and 4WD warning lights when it went.
I have the plugs and am planning on doing them just haven't had the time. that was my initial thought but I just wanted to see if there could be anything else.

Thanks.

 

If you think you have covered everything that would explain significantly decreased fuel mileage, two things: Buy and install a locking gas cap and check your fuel pressure.
I have had 1/2 tank of gas disappear in about 50 miles. I would not be surprised to see that start happening again.
tom