Bad gas mileage - no problems otherwise - where to start

[akafriday]

Hi All I have been through the other threads re: bad gas mileage. 98 OB 261K KMs, currently I am only getting a little more than 400Km/tank (60L)

 

I drive it pretty easy - and the mileage was much better before although it was the summer.

 

Based on info in the other threads on or more of the following code be the culprit:

 

1) CTS

2) MAF

3) Plugs/Wires

4) O2 Sensor pre cat

 

Here is the dilema (refering to the above)

1) Temperature of vehicle is rock solid heats up fast and sticks dead centre every time - rule out CTS?

2) MAF - no code being thrown - rule out MAF?

3) Starts great even in very cold weather, power is ok to - plugs/wires ok?

4) No O2 code - O2 ok?

 

Not sure where to start here any help would be appreciated. The knock sensor and PCV valve have been replaced - not sure if that is relevant or not.

 

Also after a repair recently I had to disconnect the battery to clear the code. I heard that you are to let the car idle for 10 minutes after this procedure to reinitialize. I did not do this - could this be the source of my problem.

 

Thanks in advance.

[nipper]

With any gas mileage complaint, first thing to do is a tune up. Plugs (factory spec) OE wires, fuel and air filter, pcv valve.

 

I would also change the front O2 sensor (OE) as it may be getting lazy. They can get tired and lazy, and not throw a code. That would give a good baseline to start off with.

 

 

Check for draging brakes, and tire pressure.

 

nipper

[akafriday]

With any gas mileage complaint, first thing to do is a tune up. Plugs (factory spec) OE wires, fuel and air filter, pcv valve.

 

I would also change the front O2 sensor (OE) as it may be getting lazy. They can get tired and lazy, and not throw a code. That would give a good baseline to start off with.

 

 

Check for draging brakes, and tire pressure.

 

nipper

 

 

Thanks Nipper - fuel filter done, air filter done, pcv valve done

 

Have not done plugs wires and O2 sensor. Where along the exhaust would i find the pre cat O2 other than obviously before the cat.

 

Cheers!

[nipper]

Lets do the wires and plugs first. The front O2 sensor will be obvious

 

I am curious to see what it comes up to before an O2 sensor change. Bad plugs can make a lazy o2 sensor even more lazy.

 

 

nipper

[akafriday]

Cheers Nipper! I will be sure to provide an update. I already have the recommend NGK plugs - is there anything special I need to use to gap them? Also what do you feel is reasonable to pay for wires? (2.5 4cyl)

[nipper]

Cheers Nipper! I will be sure to provide an update. I already have the recommend NGK plugs - is there anything special I need to use to gap them? Also what do you feel is reasonable to pay for wires? (2.5 4cyl)

 

Find one of the oneline suppliers to help you out. I know one of them will ship to upper north dakota.

 

Alos keep in mind, that winter and snow can really kill gas mileage.

 

 

nipper

[Dickensheets]

Check tire pressure. The cold will shrink the air in the tire.

 

I was in Ottawa last week. It was Coooooold!

[Reveeen]

400X .6= 240 miles

60L /4.5= 13.33 Imp gallons

 

Or a little better than 18 mpg.

 

In town, or highway?

 

I would not be seeing 20mpg here @ temperatures of -15C "in town" (in the summer with a "light foot" I see 24-28mpg in town, 32-36mpg highway).

[nipper]

So he is complai9ng about 18mpg on a high mileage car in the middle of winter.

 

bad bad human, no biscuit.

 

Thats pretty good. i get as low as 15mpg.

 

nipper

[Reveeen]

So he is complaining about 18mpg on a high mileage car in the middle of winter.

 

By my reckoning he is.

I don't even check mileage in the winter, all I know is that when the needle gets down to "E"xpensive you either put gas in, or walk.

Subaru gas gauges aren't accurate at the best of times, I *know* mine is even worse in the winter, the only reliable check is with gas receipts/distance checks.

 

I did quote Imperial gallons (that are bigger than US gallons), but before we went metric here, we were on Imperial gallons (he is probably in the 15mpg ballpark, "US gallons").

[nipper]

hehhe ill still stick by my advice, a tuneup and see where it goes. i cant promise improvement till spring or a drive to florida.

 

Imperial gallons, is that the "roayle we" gallons :-p

 

 

nipper

[akafriday]

Thanks for the insight people. 2 quick question and I already think I know what your going to say to the first

 

1) Is it absolutely necessary to use OEM plug wires? A mechanic told me the Subaru just rebrands the NGK plug wires. I know, I know OEM OEM OEM..... blah.

 

2) Could a "lazy" (thanks for the term Nipper) CTS cause the poor fuel economy I am seeing.

 

oh 1 more

 

3) Should I even bother with a tune up before spring if I am unecessarily worrying about the mileage I am seeing seeing as how 15mpg seems to not be abnormal?

 

Thanks.

[nipper]

1- Yes :-p (buy them at any autoparts store)

2- no. O2 sensors get lazy, since they are more complicated. CTS is just a thermistor.

 

3- A tuneup is never a bad thing to do. It helps the enviorment, saves you gas, and saves wear and tear on the catalytic converter.

 

Don't forget OE wires

[Rooster2]

I bought Bosch plug wires, and use Bosch Platinum plugs on my OBW from an upscale foreign car parts house. Car seems to run okay. I bought and installed these items before joining USMB, where I constantly read about only using Subie OEM parts.

 

The Bosch plug wires were expensive and work fine, it's when you buy the cheapie plug wires from AZ, Advance Auto parts, or other similar parts house that you run into trouble.

[Reveeen]

All "bets" about fuel mileage are off if you are using "MacEwens, or Drummond fuel", from up that way. Both are selling an ethanol "blend", actually substandard fuel with ethanol added, to boost the octane rating. It does not behave like conventional fuel and gives lousy mileage.

 

Rooster2:

I use "universal" Bosch wires on my older Subaru without trouble, they are solid wire wires.

[nipper]

All "bets" about fuel mileage are off if you are using "MacEwens, or Drummond fuel", from up that way. Both are selling an ethanol "blend", actually substandard fuel with ethanol added, to boost the octane rating. It does not behave like conventional fuel and gives lousy mileage.

 

Rooster2:

I use "universal" Bosch wires on my older Subaru without trouble, they are solid wire wires.

 

There is clover gas here that i can get as low as 13 out of Blu, made that mistake once.

 

Older distrubutor based ignition systems were very forgiving with wires. The newer waste type coil packs are very picky.

 

I miss my older roo's for that reason

 

nipper