2011 Ford Focus Temperature related fuel consumption

ROYHAMMY

MEMBER
2011 FORD FOCUS
2.0L
4 CYL
FWD
AUTOMATIC
123,000 MILES

When I purchased this car it had 2500 km and I got 41 MPG Imperial or 7 L per 100 KM. I was very happy and it stayed this way for about 2 years then I noticed the mileage drop into the 34 MPG imperial or 8.1 L per 100 KM. I also noticed that on very hot days my mileage improved and the engine idled so smooth you could not tell is was running. I had it diagnosed at my Ford dealer and nothing showed up. Talking to mechanics I changed the EGR valve, then the thermostat, then the AIT module as well as plugs and coils. None of this helped. I wrote to Ford to ask how many engine temperature sending units were on this vehicle that could cause this situation and they had no idea and would not replay to one of the letters. I ordered a new coolant temperature sensor and have it but have not installed it due to cash constraints. Just today I mentioned it to another quality shop and they were familiar with this problem on Ford and some other brands. Runs great on a hot day of 30 C and at about 27 id idles rough and drops in economy but the power stays the same.

5 Replies

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

With higher mileage comes engine wear which could cause lower MPG. As far as the coolant temp sensor, yes. If they are telling the computer the wrong ambient temp, it will over pr under compensate for the fuel mixture. For example, if it is 80 degrees F and the computer is told it is -30 degrees F, it will send too much fuel to the engine causing it to run rich, use too much fuel, and usually run rough.

What needs done is the computer needs to be connected to a scanner that provides real time information. Both the coolant temp sensor needs checked to see what temp it thinks it is outside. Also, fuel trims need checked as well as oxygen sensors.

Fuel trims are basically the amount of time the computer keeps an injector open based on need. They need checked to see if they are opening too long. Also, a bad oxygen sensor can cause the vehicle to run in what is called a closed loop. Basically, if the computer isn't getting a reading from an O2 sensor, it runs the engine rich to keep it going.

One last thing. Fuel pressure should be checked. If the regulator is bad, too much fuel pressure can build and cause a rich mixture.

Let me know if this helps.

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Wednesday, July 29th, 2015 AT 7:42 PM

ROYHAMMY

MEMBER
3 POSTS

Where or what is involved in the real time scan? Is there something that can be purchased and operated by a lap top. Are there different scanners that are better than others. The one at the ford dealer showed nothing at fault and my experience in past and with this vehicle is that it is hard to fix something that is not broken. Thanks for the answer I would assume that an O2 sensor would show on a diagnosis maybe I am wrong but they have shown up on other cars I have had tested. Cheers. RH

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Thursday, July 30th, 2015 AT 4:02 AM

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

A scanner can be purchased at most parts stores. As far as the issue, what I have seen happen is this. A sensor isn't working properly, but it still sends a signal to the computer. Although the signal is incorrect, the computer doesn't know the difference. As a result, it doesn't set a code. By using a live data scanner, you can see what the sensors are telling the computer as it is happening. That way you can tell if it is correct or not.

For example, I had a vehicle that ran really bad. No codes were set. Using a live data scanner or real time scanner, I was able to watch how different sensors were reacting. After checking a few, I realized the coolant temp sensor was telling the computer it was 40 degrees below 0 F. That resulted in the computer causing an extremely rich fuel mixture and the poor driveability issues. I replaced the sensor and the problem was gone. Keep in mind, there was never a code set.

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Thursday, July 30th, 2015 AT 8:01 PM

ROYHAMMY

MEMBER
3 POSTS

Thanks I have an OBI reader and I was looking at a more professional unit I think if was SCT brand, Is there a brand you suggest? I assume you just plug it in and observe as you drive? Thanks for the help these new cars are great when working properly. Then again they have the flip side.

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Friday, July 31st, 2015 AT 3:40 AM

JACOBANDNICKOLAS

MECHANIC
109,755 POSTS

I really like the Actron CP9190. I use one every day and it has held up really well. It was under 400 when I got it. I can't imagine they have gone up in price. Anyway, check it out and see if it has everything you want.