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Discussion Starter #1
Our gas mileage seemed decent until we took it to the mechanic to get it fixed. The fill up before it went into the shop was 26 MPG, the fill up after we had only gotten 23 MPG.

I replaced the air filter yesterday, because I think I heard that that helps with gas usage.

Is there any other easy (cheap) fixes underneath the hood?

I'm going to fill up the car at a different station and see if maybe it has to do with that one particular station we've been buying gas at.
 

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Try changing your fuel filter. Also, try different brands of gas. Here, I get the best mileage with ExxonMobil and Chevron. Other brands normally yield me anywhere from 30-70 miles less to the tank.
 

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also dont forget tire pressure its one of the biggest causes for poor mileage.
 

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Discussion Starter #4
Is the fuel filter something easy to do?

I filled the car up at Valero this morning instead of Wal-Mart so maybe that will change.

Before we had to take it and get it fixed we got 29, 28, then 26 MPG. After we got it back from the repairs we've gotten 23 then 21 MPG.

That's pretty bad considering the car I used to have (93 geo prizm) got 21-23 MPG and it was 13 years old when I got rid of it!
 

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A 3mpg difference between tanks isn't something to worry about. It could simply be you filled up at a different station, the average temperature outside, more stop-and-go driving than usual or any number of things. If your average MPG drops off over a large number of tanks, then you may have an issue. Also, make sure you're dividing the number on your trip odometer by the number of gallons you put in it when you fill up. If you're just dividing by the 14 gallons the tank holds you'll never get an accurate number.
 

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maybe try those fuel addictives to clean the fuel system, and check the sparkplugs
 

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Sounds to me like you have a different issue goign on there then the one you took it to the mechanic for. Start with small things like checking spark plugs, air and fuel filter and such and they work your way up to checking sensors.
 

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Discussion Starter #10
Well we went from about 280 miles on 3/4ths of a tank of gas used and this last time we filled up we only got about 190 miles out of that tank of gas and we even let it go lower than 1/4th of a tank left. So the mileage has gone down considerably.

I filled the car up at a different gas station and I changed the air filter, still gotta run through this tank of gas before I can tell if there is a difference or not.

Maybe it is something simple like Murphys is putting water in their gas or something like that and switching to Valero gas will help that. Hopefully it's nothing that it needs to be taken to the shop for.

Before we took it to the dealership it got 29 then 28 then 26 MPG. The gas that was in the car when we got it fixed and shortly after, that tank got 23 MPG, then the tank after that only got 21 MPG. And I know before I even started tracking it online that we were getting about 270-280 miles before we had to fill up again.
 

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Discussion Starter #13
Looking at that page, if there was a faulty oxygen sensor wouldn't they have found that when they ran the diagnostic test before it got fixed?
 

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http://www.fueleconomy.gov/feg/maintain.shtml

That site only talks about using the proper viscosity grade of oil. I suppose if the oil is really, really old and had thickened, it might have a small effect on MPG, but I doubt it would be measurable. And often multivis oild tend to thin with age, rather than thicken, unless it's a cheap oil and the higher volatility fractions boil off.
 

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Yes but old oil changes it's color by collecting carbon and that is how friction increases. I do see a change when I change my oil and filter in my 99 Taurus 2-3mpgs not much but it is there.
Here is something I copyed off of that last page...


What should I do if my fuel economy is excessively low?

If your fuel economy is excessively low, your vehicle may need to be serviced or repaired. You may want to contact your dealer or a reputable repair facility to check your vehicle. The following are some of the diagnostic checks a mechanic will typically conduct for poor mpg:

Perform "On-Board Diagnostic System Check" for diagnostic trouble codes (sensors or actuators which may be malfunctioning)
Check for dragging brakes
Check transmission shift patterns for slipping, use of all gears, lock-up operation
Check ignition timing
Check owner's driving habits including A/C usage, hard accelerations, carrying heavy loads
Check emission control system
Check vacuum hoses for leaks, kinks, proper routing
Check tire pressure
Check fuel type, quality, and alcohol content
Check fuel pressure and fuel system for leaks
Check air cleaner element
Check coolant level
Check ignition system for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits, cracking or improperly connected ignition wires
Check for proper calibration of speedometer
In extreme cases, there may be engine problems such as poor compression or faulty fuel injectors
 

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ammorgan said:
Well we went from about 280 miles on 3/4ths of a tank of gas used and this last time we filled up we only got about 190 miles out of that tank of gas and we even let it go lower than 1/4th of a tank left. So the mileage has gone down considerably.
If you're gauging your mileage by the gas gauge you're wasting your time. Use the trip odometer and divide the mileage on it by the amount of gas you put in when you fill up. Sometimes I can get 200 miles by the time it hits 1/4 tank - that would average out to 18mpg by your calculations. Sometimes it's closer to 140 - 13mpg. I always end up with 20-21mpg when I fill up, though - usually 10.5 gallons to top it off and the trip odometer is in the range of 220 miles when the fuel light comes on.

Try this for a few tanks to get a correct idea of what your fuel economy is and if you're still coming out with a low number then there may be an issue.
 

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Discussion Starter #17
I'm using www.fortworthgasprices.com and the fuel logbook to figure out my MPG. I'm not doing any of the calculations myself.

7/8/2006 2.829 8.990 $25.43 48,516 Valero
6/30/2006 2.839 8.542 $24.25 48,324 Murphy USA 21.36 MPG
6/23/2006 2.699 8.859 $23.91 48,124 Murphy USA 23.41 MPG
6/9/2006 2.799 8.900 $24.91 47,889 Murphy USA 26.53 MPG
6/2/2006 2.799 9.246 $25.88 47,631 Murphy USA 28.99 MPG
5/26/2006 2.730 8.901 $24.30 47,359 Murphy USA 29.42 MPG
 

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Discussion Starter #18
As for the repairs done

Looks like transmission flush, replaced a/c compressor assembly accumulator and orifice.

Replaced power steering pump. Performed power steering flush.

"Main control valve body road test verified concern, found delayed shift from 1st to 2nd on moderate/hard excel, no delay or slip found during normal excel, EEC test found P0732, performed electronic auto trans diag. all pass, road monitor/pid monitor test pass, vehicle still has very delayed shift from 1st to 2nd gear on hard excel removed trans pan, checked all harness connection, all pass, replaced main control valve body, retest no more delay at this time trans shifting as designed after repairs.

Also said fuel pump relay sticking, replaced relay no more concern at this time.
 

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"replaced a/c compressor assembly accumulator and orifice."

Well, if your A/C wasn't working well before (low or no output from compressor = low or zero HP drain from engine) and now it is working well (good output from compressor = higher HP drain from the engine), that would significantly reduce your MPG.

Are you using your A/C now?
 
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