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Old 07-17-2013, 01:58 PM   #1
tnrknght
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Default Whered my fuel economy go???

Okay so for the entirety of my last tank of gas (Im a poor individual, I use 87 octane) I ran the car with the back half-gutted. No back seats, empty trunk, not even the spare tire. Wasn't trying to reduce weight, I was in the process of a thorough cleaning... I got about 325(ish) miles on that tank.

Same day I filled up after this I put my rear seat back in and installed my sub box/amp. Nothing has been changed mechanically within the period of either tank. Driving style hasn't differed any. Somehow Im getting maybe 120ish to this tank. Finally having a day off Im about to get under the hood as soon as Im done posting this, just wondering if anyone else has input for me?
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Old 07-17-2013, 02:02 PM   #2
mbhammerbro
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Wow that's a huge difference. You used 87 octane for both tanks?
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Old 07-17-2013, 02:04 PM   #3
JohnM10
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Can you confirm that your gas gauge is working properly. How many gallons did you have to put in to fill the tank after the 120 miles? The sending unit might have gotten effected when you reinstalled the back seats.
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Old 07-17-2013, 02:17 PM   #4
tnrknght
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I used 87 in both tanks, and the tank Im on isn't gone yet I was estimating 120ish for this tank.. Im at 97.9 miles so far on this tank, and I have a hair over a quarter left on the gauge. Both tanks were filled to full at my usual gas station, with lucas fuel additive each time (I like to stay consistant)

@johnm10 I would imagine the gauge is working properly, but cant positively confirm it until I go to fill up again. I hope I didn't damage the sending unit I was even careful putting everything back together. I kinda broke my rear deck lit taking that out so Im trying to be more gentle now :/
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Old 07-17-2013, 08:17 PM   #5
sogah87
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Do your MPG!!! That'll be much more informative than to "the tank". Because most fuel gauges show empty when there is approx. 3-4 gallons left.
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Old 07-18-2013, 12:02 AM   #6
tnrknght
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The last tank was 23.6 mpg, and when this horrible tank goes down the last quarter Ill fill up again and calculate what the mpg was for this tank.
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Old 07-19-2013, 09:37 PM   #7
tnrknght
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Okay so I finally got to fill up after 138(ish) miles to this tank, I was close enough to empty to warrant a refill and calculated 12.8mpg current... I cant imagine what could be so wrong with her to cause that poor fuel economy without tripping a CEL?!?!
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Old 07-20-2013, 02:38 AM   #8
silverton
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Using that much fuel, and no codes is crazy!

Does the exhaust smell like gas? With that much gas usage you should be able to smell it. And then there'd have to be something wrong electrically.

If it's not that, it almost HAS to be leaking, whether on to the ground, or out of a bad gas cap seal..
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Old 07-20-2013, 09:33 AM   #9
tnrknght
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Ill be honest I put the a/c on yesterday (finally got it fixed at work so its cold!) and when it was running I coulda sworn I smelled a fuel scent. Of course soon after I went to fill up, did my calculating and immediately turned off the a/c...

Ill double check the gas cap but I figured if that had a bad seal it would throw an evap code or something. Especially with that kinda fuel consumption... Ill also lok around for a leak maybe smelling it in the a/c means theres a fuel leak under the hood, perhaps in the fuel filter area. Wouldn't hurt to replace that and do a tune-up..
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Old 07-20-2013, 10:49 AM   #10
EdHilario
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Have you been keeping up with regular maintenance services?
Changing oil, spark plugs, air filter, fuel filter, etc.?
Could even be a bad front O2 sensor
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Old 07-20-2013, 11:54 AM   #11
silverton
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The A/C should only cost you 1-2mpg, unless the compressor is messed up.
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Old 07-20-2013, 06:32 PM   #12
tnrknght
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I got the car in may, did an oil change then and have put 2,000 miles since I got it. The air filter was replaced (when I installed the top mount intake) roughly a month ago. I have yet to continue with tune-up or related maintenance, however not ignoring the necessity. This coming paycheck will be the ngk plugs and wires and new fuel filter.

Ill hook up a scanner when the terrential downpours let up and see what kinda numbers Im getting back from the o2 sensors. I didnt even consider that with the lack of cel but youre right it is still possible.

@silverton As far as the a/c goes that was the only time using it over the past month because it was not fully functioning... which wierdly enough when we hooked it up to check the pressures it apparently was really high pressure but not of 134 the mass/pressure didnt make sense...
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Old 07-21-2013, 02:39 PM   #13
FOGeologist
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Is the power delivery goofy?

Here's stupid question - did a relative drive the car and reset the trip odo? Got any clever teen-aged boys in the house?

Could your gas have been stolen?
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Old 07-21-2013, 03:32 PM   #14
silverton
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I forgot to mention earlier with that much fuel "usage", if it is going in to the combustion chamber, your oil will be heavily saturated with fuel because it's able to get by the piston rings. So your oil will be heavily saturated and fuel eats bearings pretty bad. Take the oil cap off and see if it smells very badly of fuel, if so, do an oil change PRONTO. Along with that, your catalytic converter is going to be working very hard and the exhaust will smell of rotten eggs and eventually ruin and clog it, because it gets so hot it melts itself.
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Old 07-21-2013, 03:33 PM   #15
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Quote:
Originally Posted by FOGeologist View Post
Could your gas have been stolen?
I've tried siphoning my own gas, MY01, and the tube can't make it to the fuel.
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Old 07-21-2013, 03:48 PM   #16
FOGeologist
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Quote:
Originally Posted by silverton View Post
I forgot to mention earlier with that much fuel "usage", if it is going in to the combustion chamber, your oil will be heavily saturated with fuel because it's able to get by the piston rings. So your oil will be heavily saturated and fuel eats bearings pretty bad. Take the oil cap off and see if it smells very badly of fuel, if so, do an oil change PRONTO. Along with that, your catalytic converter is going to be working very hard and the exhaust will smell of rotten eggs and eventually ruin and clog it, because it gets so hot it melts itself.
This is good advice. I'm having trouble believing that the throttle body could "stick open" and flood the motor like this and the car would run without setting a code, however, and I'd think the car would run very poorly with gas running down the cylinder walls and into the crankcase.
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Old 07-22-2013, 03:21 AM   #17
silverton
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Quote:
Originally Posted by FOGeologist View Post
This is good advice. I'm having trouble believing that the throttle body could "stick open" and flood the motor like this and the car would run without setting a code, however, and I'd think the car would run very poorly with gas running down the cylinder walls and into the crankcase.
If the throttle body was stuck open, the idle would be high.
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Old 07-22-2013, 08:50 PM   #18
sogah87
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I don't think I read a response to how the car is actually running? That much fuel cannot be disappearing, so where is it going? Some one asked earlier about the oil, as well as the car's performance.

OP, are you mechanically inclined? Do you know how it should feel? Can you determine if there is a leak/sludge in the engine bay? Give us more clues lol.
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Old 07-26-2013, 06:01 PM   #19
Calidinho10
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Try driving the car for a little while, or as soon as you get home from work or something. Then feel the wheels and tires. If the tires are hot to the touch then they could be over/under inflated. If the wheels are hot to the touch its probably from the brakes. You could have a dragging caliper. Based on the other information I would check your transmission and differential fluids and make sure they are at proper levels and do not smell burned.

If all of this doesn't help then it's time to take it to a dealer.
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Old 07-30-2013, 08:42 PM   #20
tnrknght
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Sorry for the late response, Ive been working 7 days a week lately. Being a service tech at Pep Boys I am just a little mechanically inclined, At least I thought so when I swapped a motor into my legacy .

As far as the performance aspect of it, the car has been running the same, sometimes feeling just a little lazier than usual. I would honestly hope that the gas was stolen, I drove out the last tank and refueled yesterday, after 305.4 miles I calculated 22.75 mpg. So the record is: 23.6mpg, 12.8mpg, 22.75mpg from one tank to the next with no changes in driving style or mechanincal in any way.

I have since checked the oil (I check my fluids regularly) and no notice of a fuel smell. I do intend to do another oil change when the new tune-up parts come in. I don't trust my stores parts so I order elsewhere. NGK plugs and wires and OEM Subaru oil and fuel filters should arrive anytime. I don't know too much about the history of the car so I don't wanna go half assed on it
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Old 07-30-2013, 08:47 PM   #21
tnrknght
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Quote:
Originally Posted by tnrknght View Post
I am just a little mechanically inclined, At least I thought so when I swapped a motor into my legacy .
Just so no one gets the wrong idea thinking Im a pompous ass or anything, anyone who knows me knows the story of trying last summer to put a 99 (map) motor into my 98 (maf) legacy wagon and all the headaches it gave me til I finally decided to pull the motor back out and find another maf, which I have been continuing to this day.

So no self-centeredness, just poking fun at myself lol
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