Lousy gas mileage

[bulwnkl]

Can't give you the big highway sign, just look upstream of the big catalyst.

 

 

One thing that's not expensive that you could try is Auto-RX. I don't know that I really think you need it, but if all else fails it's not hard to try. Put a .com after that name and you'll get to it.

 

I'm really interested to see how this goes for you, and wish you good luck. There is always the possibility that this is just one of those engines/cars that doesn't get good mpg (like how there are some that just make more power than all the others, etc). I hope that's not true here.

 

 

P.S. If you've been shooting a bunch of carb cleaner/MAF cleaner type stuff into the intake, I'd change the oil sooner than later.

[86BRATMAN]

Look at the stock exhaust pipes and follow from where they joint behind the engine. The primary o2 will be between the join and before the catalitic convertor.

 

 

Also, did you use dedicated MAF cleaner or carb spray on the maf?

[eryque]

Who makes the OEM sensors? My local parts place carries the Bosch 02 sensor, and if I'm gonna take it off to inspect it I might as well replace it since I'm coming up on its replacement interval anyway.

 

 

I used CRC's MAF cleaner on the MAF and their throttle body cleaner on the throttle body. Pretty ingenious of me, huh?

[86BRATMAN]

The best place to get the sensor is from the dealer, you'll pay more for it, but its worth it. There is a number listed on the sight for a Jason who works for a dealer out west who can hook you up with a good deal.

 

 

Just had to check about the maf cleaning... Can't be too careful with those.

[eryque]

I figured that I was working on the car today anyway, I might as well get one and do it while I'm dirty. Besides, Subaru doesn't make the part, they buy it from Bosch or someone else, so I'd rather save some $$ and go direct to the source if I can.

 

But moving on from that, where's the knock sensor? Chiltons says very vaguely it's on the top left of the cylinder block. I didn't see much there except the injectors, plugs, and intake manifold.

[86BRATMAN]

Look at the back of the motor, to the driver's side of the throttle body. Down on the block, single wire running to it.

[eryque]

Found it just before you posted. Thanks though

 

How the heck would you get that off? Do you have to remove the hose to the throttle body and mayb use a wobbler extension?

 

I inspected it visually and it looks good. I suppose I could replace it and see if that helps, but I hate just swapping parts to see what works.

 

Do these things have life expectancies? I aw that the o2 sensor should be replaced every 100,000 miles, is it similar for the knock sensor? Or do you just wait for them to go bad?

[porcupine73]

You don't have to take the throttle body or anything off to get the knock sensor out. Yes just use a wobbler extension and maybe flex joint if needed. Not sure about the impreza, but on my legacies I can get my hand down in there by reaching in to the side of and below the throttle cables.

 

For the front o2 sensor, really oem is the way to go. Order it from a Subaru dealer who sells parts online to save $ over going to the local dealer (unless they'll price match or happen to wholesale parts).

 

Some earlier Subaru's the o2 sensors were Bosch, some are Denso. The way to get the right one with the connector for your vehicle is to get it from Subaru. Even though the parts store sensor might be made by the same manufacturer, it may not be the same specs. If you get a bosch generic, you'll have to cut the connector off your old sensor and solder the wires onto the new sensor.

 

Also physically inspecting the o2 sensor isn't going to tell you a whole lot.

[eryque]

I meant that I visually inspected the knock sensor. On mine I couldh't even see it uness I stuck a wrench down there to push the hose and wires from another circuit to the side, I couldn't really get my hand down there either.

 

I went to run some errands and got a CEL with a code (P0141) O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2). Cleared the code and it didn't come back.

 

Sound like a bad O2 sensor, or maybe just coincidence since I was mucking around down there?

[porcupine73]

P0141 is for the rear o2 sensor. Did you unhook any connectors or anything?

DTC P0141: REAR OXYGEN SENSOR HEATER CIRCUIT MALFUNCTION (RO2H)

[NoEyeSquareGuy]

Anyone have a line on cheap knock snsors? I've long suspected that mine may be bad... rockauto.com's price is ~$86(!). Anyone seen anything cheaper?

[porcupine73]

$86 wow. That's more than OEM. 22060AA070 Forester 1999-2002 knock sensor msrp $97. Can be had for $78 from Subaru dealers who sell parts online. There might be other cheaper aftermarket alternatives if that is the desired route.

[eryque]

P0141 is for the rear o2 sensor. Did you unhook any connectors or anything?

DTC P0141: REAR OXYGEN SENSOR HEATER CIRCUIT MALFUNCTION (RO2H)

 

argh.... no didn't touch the rear one. Is it possible that a bad rear o2 sensor could cause lousy gas mileage?

[porcupine73]

No, rear o2 sensor is purely an emissions/catalyst effiency purpose.

[fnlyfnd]

I constantly avg. 22mpg in my '96 2.2 5spd. New O2 and complete tune up didn't change my economy.

[eryque]

after cleaning the MAF and throttle body i drove it for 94 miles w/o the a/c, about 80% of it on the highway at 10 mph over the posted limit, which put me at 75 mph most of the time. 94 miles on the odometer and 3.2 gallons of gas.

 

i like that.

 

i have a feeling it was mostly the a/c bogging me down.

[bulwnkl]

I've definitely had cars that, no matter whether it's possible or not, definitely had the mpg CRUSHED by the A/C. Some others don't seem to care much. For me, the smaller the car/engine/hp, the bigger the difference in mpg with and w/o A/C. I hope that's all it is for you!