Sudden MPG decrease

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RamFan

RamFan

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I've recently been hit with rather low MPG on my Charger. I know that many things can cause a decrease in MPG but I'm going to ask the question anyway. What are some possible causes of a sudden decrease in efficiency? I've already checked the PCV, thought that since the Charger burns roughly 1qt/1k miles it might have fouled the plugs early so I'm going to change the plugs next week (going to do a compression test as well).

1/23/13 - 12.9mpg
3/2/13 - 14.4
3/29/13 - 15.1

Before this I was normally getting 16.5-18.5 in town. I literally went from getting my usual mileage to the 12.9 figure and ensuing values out of no where. The car drives the same, no power loss, nothing funny going on mechanically. I'm kind of lost.
 
Originally Posted By: Donald
Change in temp, need to re-inflate tires?

E10 might now be E10 and was E8 before.

How are you measuring the MPG?


Tire pressure is good, just checked yesterday actually.

I use Fuelly. The interesting thing though is that my highway MPG isn't really any different (hard to remember exact trips just by looking at dates) than before. So it seems as though the problem is only a problem around town and not on the highway.
 
Got a slightly stuck caliper? If you can get your hands on an infrared gun, check each corner to see if one is hotter than the others. I found a sticking caliper on my wife's old Civic this way.
 
I would check the Coolant Temp. Sensor/CTS. If defective, it is like having the choke on all the time in the 'good, old carb' days. The CTS is rel. cheap and easy to replace. It is telling the PCM/ECM that the engine is cold and you need to enrich the gas/air mixture.
 
Originally Posted By: Jim Spahr
I would check the Coolant Temp. Sensor/CTS. If defective, it is like having the choke on all the time in the 'good, old carb' days. The CTS is rel. cheap and easy to replace. It is telling the PCM/ECM that the engine is cold and you need to enrich the gas/air mixture.


I was thinking that to be a possibility, would a failing CTS not affect the coolant gauge? Because my gauge is acting fine.
 
Originally Posted By: danthaman1980
1 qt/1k miles on an '07 ?!?! Ouch!


Yeah that's pretty typical of this engine for some reason.
 
Originally Posted By: gathermewool
Got a slightly stuck caliper? If you can get your hands on an infrared gun, check each corner to see if one is hotter than the others. I found a sticking caliper on my wife's old Civic this way.


Interesting theory, I'll look into that.
 
Wow...1 qt./1,000 miles w/56k on the clock is "normal"?...I've never owned a vehicle that used oil like that at ANY mileage. I'd be more concerned about the longevity of the engine than the mpg decrease.
 
I just experienced sort of the same problem in a 2003 Acura MDX. The gas mileage had been slowly decreasing after 125,000 miles but after 150,000 started decreasing faster and after 155,000, fell off the table, dropping from 19-20 on the highway to under 17 (whereas pre-125,000 it had been around 23 on the highway). I had several shops attempt to figure it out, including checking compression, plugs and anything else, and nobody could come up with any answers. Our solution was to trade the car. Whatever is going on with your car is not good, and it's probably serious. Good luck. I feel like we traded our's just in time. I was expecting around 19 mpg on our trip to see the dealer and was flabbergasted myself to see it only did 16.7. I would seriously consider trading the vehicle.
 
Originally Posted By: danthaman1980
1 qt/1k miles on an '07 ?!?! Ouch!


People will tell you its 'common', but I will tell you its not 'normal.' A mis-routed PCV hose can increase oil consumption, so can a bad PCV valve. I'm assuming this is a 3.5, and I'll bet a cheeseburger its is NOT burning that much past the rings or guides. This 'common' behavior seemed to start well after the gen-II 3.5, and I blame the PCV system in the later vehicles. Catch can time to prevent fouling the plugs or retarding the timing through increased pinging.
 
Some of these were probably mentioned, dirty MAF sensor, brakes dragging, upstream O2 sensor, and spark plugs would be likely culprits. With the oil consumption the spark plugs and O2 sensor could be partially fouled up.
 
Originally Posted By: 440Magnum
Originally Posted By: danthaman1980
1 qt/1k miles on an '07 ?!?! Ouch!


People will tell you its 'common', but I will tell you its not 'normal.' A mis-routed PCV hose can increase oil consumption, so can a bad PCV valve. I'm assuming this is a 3.5, and I'll bet a cheeseburger its is NOT burning that much past the rings or guides. This 'common' behavior seemed to start well after the gen-II 3.5, and I blame the PCV system in the later vehicles. Catch can time to prevent fouling the plugs or retarding the timing through increased pinging.



Yes it's the 3.5l, I've contemplated a catch can decided it wasn't worth it. Didn't realize a catch can could reduce fouling though?
 
A sticky caliper can usually be found by the car not moving under no throttle from a flat start from stop sign or red light as well. I had this on my old montero and some brake work and slides lubed cured it. it would actually hold still until pressing gas pedal. Afterwards would go forward under idle only.
 
Or just go to a parking lot with a little bit of a hill. Put it in neutral and see if it rolls like it should. My 07 Mustang had a sticking caliper on the back right wheel and would stick when it was really cold (below 25) and would stick for a few minutes and then release. you could actually feel when it released.
 
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