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Discussion Starter #1
Hey all, have a question that I'm not so sure where to post, hope I ended up in the right section.

So I have an 03 WRX Wagon. Only mods (engine at least) are a gutted up pipe and a perrin turbo inlet hose. Also, it has the K&N filter, but stock airbox and all that. Just over 100k miles, recently done spark plugs, no idea when the O2 sensors were last done but they don't look like they have 100k miles on them.

Recently I've noticed a slight drop in MPG and I can smell that It's running rich. I've reset the ECU a couple times recently due to working on the car (all suspension stuff but I still unhook the battery) and the mpg and smell will be decent for a tank or two, then back to crappy/smelly.

So, could a bad O2 sensor or something else cause the car to run rich, or is it maybe time for engine management? Or could it be something different entirely that I fail to think of? And I don't think it's driving style, because recently I drove a 350 mile freeway trip with cruise control set at 80 and on the way up, I made it on one tank (freshly reset ecu) and on the way back, I had to stop for gas about 280 miles into it. Also I don't think either of my "mods" have to do with it, because I've had both installed for a couple months before I noticed my car running rich like this.

Wow sorry this is such a long post, I just want to give you guys as much info as I can, plus I feel it's kind of a weird question.

Anywho, thanks in advance for any help on this. BTW the reason I don't just get new O2 sensors and a tune (and new tires, and exhaust, and rims, and swaybars, and a Porshe) is because I'm broke!!!
 

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Check your tire pressure. As for smell,the ECU targets 14.7:1 AFR in closed loop. Even if you were only getting 14:1 AFR you would not be able to "smell" the difference. Maybe you have a slight fuel leak,which is very common with the bugeyes. There was a TSB about a leak at the fuel rails. Also if the ambient temps have dropped recently then that will cause your mpg's to go down. Longer warm up times and colder IAT's will use more fuel. A OBDII scanner can verify if the front O2 sensor is having problems. It is the primary AFR sensor.
 

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Discussion Starter #3
You know I have been having tire pressure problems, good call! Tires are first on my list of **** to buy once I get money.

OBDII scanner comes up clean. I'll poke my head around and check out the fuel rails too. What's IAT again? Oh intake air temp... I always thought cold air would give you better mileage.

Thank you Donkey, this is exactly what I needed to hear. You know how sometimes you start to notice problems on your car that aren't really there, or become super sensitive to small changes that are probably normal but you somehow turn into bigger problems because you just can't turn your brain off? Yeah, me too.

So do you know where can I do some research on the stock ECU? I'd love to get some info on how it works. That sort of thing really interests me; I have a minor background in programming. I know sometimes I sound like an idiot but there IS a fully functioning brain in there somewhere.
 
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