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Up until very recently, my car has been getting about 24-26 mpg. However, with the recent hot spell, I've been running the A/C much more, and I have noticed a significant drop in fuel economy and power, down to about 18-20 mpg. It now feels like I have an additional 500 lbs in the back when accelerating, and I can feel a jolt of power in the car when the A/C switches off (it still cycles on and off properly). In addition, the car has been taking a few extra seconds to turn over when cranking. I added Techron to the previous tank of gas, and I didn't notice any problems during that tank. The fuel filter only has about 5k miles on it, and the car has about 47,000. I've run this car previous summers with the A/C, and I have never noticed this much of a power/mileage hit.

Questions
-Could the power drop signal a problem with the compressor bearings or clutch? If my refrigerant is getting low, will this put a bigger load on the engine?

-Did the Techron do something to my injectors/fuel system? I've used it several times before without issues.

-Are my O2 sensors going? No trouble codes yet.

-Do I just attribute it to really bad gas? I put in no-ethanol premium from a station I've used a dozen times before (no previous problems).

This all seems rather strange to me, and I would appreciate any ideas. Thanks!
 

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Discussion Starter · #2 ·
Ok, I see the new site doesn't put my car info in the side pane anymore. Here it is:

2006 Taurus SEL Vulcan engine 47,000 miles

Sorry guys!
 

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I barely make 20 mpg with the A/C off >_>
 

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Up until very recently, my car has been getting about 24-26 mpg. However, with the recent hot spell, I've been running the A/C much more, and I have noticed a significant drop in fuel economy and power, down to about 18-20 mpg. It now feels like I have an additional 500 lbs in the back when accelerating, and I can feel a jolt of power in the car when the A/C switches off (it still cycles on and off properly). In addition, the car has been taking a few extra seconds to turn over when cranking. I added Techron to the previous tank of gas, and I didn't notice any problems during that tank. The fuel filter only has about 5k miles on it, and the car has about 47,000. I've run this car previous summers with the A/C, and I have never noticed this much of a power/mileage hit.

Questions
-Could the power drop signal a problem with the compressor bearings or clutch? If my refrigerant is getting low, will this put a bigger load on the engine?

-Did the Techron do something to my injectors/fuel system? I've used it several times before without issues.

-Are my O2 sensors going? No trouble codes yet.

-Do I just attribute it to really bad gas? I put in no-ethanol premium from a station I've used a dozen times before (no previous problems).

This all seems rather strange to me, and I would appreciate any ideas. Thanks!
If you were low on refrigerant then the A/C wouldn't turn on at all. If it was the bearings, you'd also be hearing abnormal noise. If it was the clutch, the A/C would be making noise and you'd notice it either sticking on or not going off.

If it was your O2 sensors, you'd be getting a trouble code and check engine light.

Your car isn't designed to run on premium, but it shouldn't affect gas mileage that much.

Maybe it's time for a tune-up.
 

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While my comment here doesn't offer any help towards your problem, I just wanted to state that my 60,000 mile '06 Vulcan gets 24-25 mpg @ 75 mph with the AC on or off. But, I notice a lot of things like that with my car. It doesn't have any of the quirks or issues that a similarly millaged Taurus does and I'm not exactly gentile with it. Weird.
 

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My average MPG with an even mix of city and highway is about 20. With the A/C on a lot it will drop to about 15-16. With A/C on I have a loss of power as well. Very typical for the 3.0 OHV.
 

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I've seen a similar problem with older Taurus' wherein the A/C kicks on and the car loses power. Press the accelerator to the floor and it makes good power, but mid-range its flat. In those cases it can SOMETIMES be the A/C - Fuel Pump relay. On older Taurus' the relay is on the core support, under the top plastic cover. When an A/C or fuel pump relay is bad it lowers power to the fuel pump when the A/C - Fan combo kick on. It's hard to tell if this could be an issue for you in this case though. And with less fuel (lower pressure) the EGR still functions but the car runs lean.

Then again, you're experiencing a loss of MPG, so I could be way off.
 

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OP: Are you computing your MPG by hand? Or are you guaging based on the dash computer? Because the dash readouts are not particularly accurate.
 

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No one point out that the weak transmission could indeed be the culprit.

My 04 Sable vulcan behaved sometimes. One day it may be tough to
drive, you press the gas half way down, and the speed just SLOWLY
climbed to 20mph as if it's pulling a big trailer. But the next day, it
may just feel so much smooth. You barely touch the gas pedal, and
the speedometer sprinted to 25mph in 2 seconds.
The engine was fully tuned up with new spark plugs, wireset,
Mobil#1 oil, MAF cleaned, etc. The 2 front wheel bearings were replaced
since I doubted worn bearings could add extra frictions in the power chain.
Finally I realized the weak AX4N transmission could be the real trouble maker.
It has been overhauled for $1600 last year, and I'm not confident in it at all.
The car just suddenly neutraled out without any preliminary symtoms on the interstate.
So dangerous!!
I have no clue how the tranny was built. But apparently it was not
tuned to its best. I ever asked my dealer if they can re-flash the ECM to upgrade
the software. But they are not willing to offer this service without any engine error codes.
You can try some fully synthetic ATF and see if you can find a difference.
I would say, take good care to this fragile tranny, since it may fail you
in your least convenient situation.

Up until very recently, my car has been getting about 24-26 mpg. However, with the recent hot spell, I've been running the A/C much more, and I have noticed a significant drop in fuel economy and power, down to about 18-20 mpg. It now feels like I have an additional 500 lbs in the back when accelerating, and I can feel a jolt of power in the car when the A/C switches off (it still cycles on and off properly). In addition, the car has been taking a few extra seconds to turn over when cranking. I added Techron to the previous tank of gas, and I didn't notice any problems during that tank. The fuel filter only has about 5k miles on it, and the car has about 47,000. I've run this car previous summers with the A/C, and I have never noticed this much of a power/mileage hit.

Questions
-Could the power drop signal a problem with the compressor bearings or clutch? If my refrigerant is getting low, will this put a bigger load on the engine?

-Did the Techron do something to my injectors/fuel system? I've used it several times before without issues.

-Are my O2 sensors going? No trouble codes yet.

-Do I just attribute it to really bad gas? I put in no-ethanol premium from a station I've used a dozen times before (no previous problems).

This all seems rather strange to me, and I would appreciate any ideas. Thanks!
 

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I only get 15 MPG in the city with A/C on and a lot of idle time. I get 30 MPG pure hwy with A/C on.

Thats just how it is, the compressor takes horsepower and it injects more fuel just to keep you at even idle.

Less of a loss on the highway due to higher horsepower being made at higher revolutions that you see at interstate speeds like 2500+ RPM
 

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I drive 100 miles a day in the 100 degree heat heare in florida :( I notice everything you mention and I average about 20mpg most of the time.

it's so hot here it's making my temp gauge rise :unsure:
 

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Mine is the same way with the a/c on. I lose about 3 mpg overall, compaired to not running a/c, and it's like I'm pulling a trailer. I just drove mine back to Austin, TX, from Minneapolis, MN. The first half of the trip, I didn't run a/c, and got 29.2 mpg. After Kansas City, MO, I was bucking a wind, and running the a/c, got around 26.4 mpg. The trip computer does give a general idea of mpgs, but is never 100% correct. I was able to drive well over 400 miles per tank during the trip. My temp gage has never rose above the usual mark, even when it's over 100 degrees here.
 

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Chenrip,

you may have a failing Vehicle Speed Sensor.

When I replaced my failed transmission '99 with Ford Reman unit,
I experienced the same symptoms plus late upshifts from first to second.

it took a week before it started to give fault codes.

Behlina,

I run premium in my cars since purchased used with 25K in 1999,
I get about 23MPG but I drive 90% on interstate in Raleigh NC 70mph avg.

take a look at the PCV valve, sometimes the rubber grommet gets soft and
has poor seal as well as the hose from PCV to the intake manifold, it gets very very
hot back of the manifold and that dries out the hose and you get vacuum leak.


regards
 

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Thanks, James27613.

But without check engine like ON, thus triggering a fault code,
it's really hard to tell the Speed sensor is faulty. I used GPS
on the interstate, and the reading from GPS agrees well with
my speedometer reading.

The car is OK in winter, fall, spring. But in the hot
summer like these days, the transmission or engine becomes
really LAZY to work. You have to press the gas pedal deeper to
drive the car at its normal speed. Gas mileage also drops.

If it is the transmission, my guess would be:
1) worn solenoid, when a shift signal was sent to it, it takes
extra time for the magnetic part to actuate, thus a late shift.
2) poor transmission fluid, thus not sufficient lubrication

Chenrip,

you may have a failing Vehicle Speed Sensor.

When I replaced my failed transmission '99 with Ford Reman unit,
I experienced the same symptoms plus late upshifts from first to second.

it took a week before it started to give fault codes.

Behlina,

I run premium in my cars since purchased used with 25K in 1999,
I get about 23MPG but I drive 90% on interstate in Raleigh NC 70mph avg.

take a look at the PCV valve, sometimes the rubber grommet gets soft and
has poor seal as well as the hose from PCV to the intake manifold, it gets very very
hot back of the manifold and that dries out the hose and you get vacuum leak.


regards
 

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hi,

this is one symptom of a bad VSS sensor.
the sensor sits on top of the transaxle near the
exhaust system and converters and they get HOT.

would explain why it runs better in the cold weather.

cost about $25 to replace it yourself

regards

The car just suddenly neutraled out without any preliminary symtoms on the interstate.
So dangerous!!
 

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Thanks, James27613.

But without check engine like ON, thus triggering a fault code,
it's really hard to tell the Speed sensor is faulty. I used GPS
on the interstate, and the reading from GPS agrees well with
my speedometer reading.

The car is OK in winter, fall, spring. But in the hot
summer like these days, the transmission or engine becomes
really LAZY to work. You have to press the gas pedal deeper to
drive the car at its normal speed. Gas mileage also drops.

If it is the transmission, my guess would be:
1) worn solenoid, when a shift signal was sent to it, it takes
extra time for the magnetic part to actuate, thus a late shift.
2) poor transmission fluid, thus not sufficient lubrication
The problem could also be that when the air becomes dense with humidity, it affects the combustion temp. Mine also gets that way when the air become very dense during the long hot, humid Texas summers. When that happens, I will put up with it, or use premium gas. The premium gas seems to help with the problem when the humidity and temps get very high. The Buick I had before this car also became more sluggish when the air becomes very dense.
 

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AC reducing gas mileage by 5 is groundless. Real test data indicate no difference between [AC on, window closed] and [AC off, window down].
 

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I havee an older taurus (95' 3.8) and have tracked gas mileage for more than 8 years (using the odo and trip odo, they are the same) and I get around 21-23 mpg during the "winter" and during the summer I get low 17's high 16 mpg during the summer. My drive to and from work is a mix of highway and city driving. I say summer and winter because the summer is the only time I run the AC so that's the only time I see a change in mileage other than all highway drives where I usually get 26 mpg. This year is a little different because the suction/discharge line got a hole in it and I haven't had a chance to fix it, so this summer I am right at 21-23 still but would love to get 16-17 if the AC was working.

Jeff
 

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AC reducing gas mileage by 5 is groundless. Real test data indicate no difference between [AC on, window closed] and [AC off, window down].
Please indicate sources for that kind of statement. Car and Driver tested this and the data concluded that A/C on does effect gas mileage.
 

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The car just suddenly neutraled out without any preliminary symtoms on the interstate.
So dangerous!!

There is definitely something wrong with the Gen 4 Taurus transmissions. I think they used cheaper parts or something. My brother's '01 Taurus transmission just jumped forward one day driving down the road and wouldn't go anymore. No warning or anything. Had to have the whole transmission rebuilt.

At least with the gen 3's and older, you'd notice slipping and all kinds of other problems, and the transmissions would die slowly. But these gen 4's seem to just pop out.
 
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