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Old 01-20-2004, 07:21 PM   #1
ImprezaVA
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Default 16 mpg 2.2

I've posted in a couple of oxygen sensor threads about poor gas mileage. One week its around 25 mpg, the next its 19 mpg. Well today I filled up at BP and when I divided the gallons bought and the trip I averaged 16 mpg.

Whats the poorest gas mileage you'll have gotten without a CEL?
Should I replace my plugs now? I mean, I know my car must be running rich, real rich, as our cars naturally run a little rich anyway. There was some yellow build up on my muffler tip also, is this the carbon or unburnt fuel?

Those O2 sensor connectors are a pain to get off, at least I had trouble, anyone got any tips?

New air filter and fuel filter, new plugs 12,000 miles ago, new oxygen sensors on the way. I'm going to replace both no matter what b/c I believe these were the OE one's so they now have 93,000 on them.

-Charles
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Old 01-20-2004, 09:45 PM   #2
Kamen
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On either of my Legacy 2.2L cars I have always gotten above 20mpg and that's the worst case scenario (single-digit temps, stop-and-go driving, etc.) If you have access to an OBD-II scan tool use it to observe the O2S outputs - you should be able to tell if the sensors are bad (and which) or the cat is getting inefficient (or plugged). O2S can last very long - my 1995 has 180K+ miles and only now it's starting to exhibit problems (and I can't tell if it's the sensor or the cat). Yellow residue on the pipe? That's weird. If unburnt fuel is getting there you can bet your cat is as good as gone. If I were you I'd have it looked at by someone experienced.
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Old 01-21-2004, 08:45 AM   #3
OBS Fan
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Yellow build-up is likely sulfur from using a high-sulfur fuel. Does your exhaust smell like rotten eggs? That's sulfur.

Run the gas tank down to empty and fill up at someplace other than your typical BP station. I like Mobil/Exxon. See if this changes your mileage.

The worst I've seen with the 2.2L is about 23 mpg.

Good luck.

-OBS Fan
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Old 01-21-2004, 01:22 PM   #4
ImprezaVA
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I've always used Exxon/Mobil Gas, that's why I'm expirimenting with BP. I'd like to find someone with an OBD II tool that can check oxygen sensors. I have a digital multimeter but don't have time to check the voltage now that school is in.

The sulfur stain on the exhaust tip polished right out. I don't have the rotten egg smell of bad converter either. I just wish I had time to check those O2 sensors, but those pesky connectors are a pain to get to and get off.

-Charles-
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Old 01-21-2004, 11:50 PM   #5
vvk
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Quote:
Originally posted by ImprezaVA
I'd like to find someone with an OBD II tool that can check oxygen sensors.
An OBD-II tool is not going to show anything if your CEL is off. You can get a local AutoZone to pull your code for free. I just had it done today -- they were very nice and helpful.
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Old 01-22-2004, 09:28 AM   #6
ImprezaVA
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Quote:
OBD-II tool is not going to show anything if your CEL is off.
I used to think this also until I heard someone mention that a guy checked their O2 sensors voltage through some OBD II tester.

With this new BP gas I bought earlier this week I got 100 miles to the first 1/4 tank, when last time I got just 48 miles on a 1/4 tank . Same commute, same type of driving, same temperature, altitude, etc. I have a feeling that it's not just the gas and the O2 sensor is just fluctuating. This weekend I'll make time to check the sensors with my multimeter and let you guys know how it turns out.

-Charles-
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Old 01-22-2004, 04:09 PM   #7
Charlie-III
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Also check your plug wires. They may be arcing on the coil pack.

They should be changed anyway if they are original.

What plugs did you put in? I have heard of too many problems with Platinums.

So, I say stick with OEM plug wires and NGK copper plugs. The copper plugs need to be changed a bit more often, but they are cheaper and don't create problems.
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Old 01-22-2004, 08:30 PM   #8
sdogg3kgt
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I get 15mpg right now on average. Just passed 9000 miles on my car.

I guess it's due to the fact that we had a lot of snow recently, so I kept the car in a lower gear at all times.
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Old 01-25-2004, 12:25 AM   #9
Raptor75104
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Quote:
Originally posted by ImprezaVA
I've posted in a couple of oxygen sensor threads about poor gas mileage. One week its around 25 mpg, the next its 19 mpg. Well today I filled up at BP and when I divided the gallons bought and the trip I averaged 16 mpg.

Whats the poorest gas mileage you'll have gotten without a CEL?
Should I replace my plugs now? I mean, I know my car must be running rich, real rich, as our cars naturally run a little rich anyway. There was some yellow build up on my muffler tip also, is this the carbon or unburnt fuel?

Those O2 sensor connectors are a pain to get off, at least I had trouble, anyone got any tips?

New air filter and fuel filter, new plugs 12,000 miles ago, new oxygen sensors on the way. I'm going to replace both no matter what b/c I believe these were the OE one's so they now have 93,000 on them.

-Charles
Tip of the day: If you want to check your cat(s), get a hold of a pyrometer. The temperature coming out of the cat(s) should be higher than the temps going in. If not, then your cat or cats are trashed. As Subarus have a pre-cat and a cat, you can check both. Anything before, say, 97 (not sure about the 97 model year) has a cat assembly meaning the cats can be purchased separately. But be forewarned that if one is bad, but the other is not, the other one is on the way out shortly. Anything after that model year has two cats in one assembly. Also, if you're solely depending on a scan tool to diagnose your car, don't be fooled. Things can be wrong and not trigger the MIL.

Charles, you're definitely due for new cats and/or 02 sensors. Since you have new 02 sensors on the way, start thinking about your cats.

Raptor
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