subie07

My car stats:
2007 WRX with a TBE

So just like most subie owners I occasionally gun, but drive fairly conservatively on a daily basis. I drive a total of about 54 miles round trip to work and back. I thought my car might be consuming too much fuel, so I decided to fill up and watch the gauge. So on Wed this week I filled up my tank all the way. Today it's down to just about a 1/4 tank. So from wed till today I drove 162 miles, started with a full tank, and now down to a 1/4. That's absurd!! Any ideas what could be causing this? Something very similar happened to me back in 2011. I took it to the dealer, and Subaru said one of my injectors was leaking. They replaced all 4 and it ran fine.

CHESTON

iTrader: (19)

Wow. I would kill to get 154 per half tank. I average 124 per half tank! Course this is thanks to driving in commute traffic.

subie07

Well I used to be able to drive almost two weeks on a full tank, and now I used 3/4 in 3 days. Think maybe the addition of the DP might have something to do with it?

CHESTON

iTrader: (19)

Haha, ummmmm yes.

Maybe give us a timeline of what mods you did and you MPGs from those times? Also, did you get tuned for your DP? Those play a big difference. Also how heavy your foot is.

When I went to stage 2, DP and tune, I actually crept up in MPGs. Andddddd then I decided that enjoying the POWAH was moar fun. Just gotta pay to play.

Many years later (read wear and tear) on the power train, multiple mods later and a commute that is typically below 50mph on highway...I'm down to ~17mpg on avg tank. Back in the good Ol days I was getting ~150-160 on a half tank...right after the changes.

assuming you've been doing regular maintenance on your engine, answer the above questions and you'll get better feedback from the community.

subie07

I had a cat-back for a while, and it ran fine. About 2 months ago I added the DP. No tune because I didn't know you had to tune something like that. My foot was heavy at first cuz the extra power was fun, but then cooled down. I've been doing regular maintenance too.

CHESTON

iTrader: (19)

Hmm. Hope no damage to your motor. When you change DP, that's a significant change to the engine flow. Get tuned ASAP To avoid potential damage to your engine.

subie07

Or I can just go back to stock DP. I know you need a tune for extra air/fuel but this is just exhaust flow. Pardon my ignorance, but how can It damage the motor if the exhaust just flows more freely?

CHESTON

iTrader: (19)

Well the turbo and stock DP affect the air/fuel parameters that your OEM ECU is dealing with.

Afternarket DP causes your turbo to increase its flow characteristics, as the OEM cat is a notable restriction. Your computer doesn't know how to / have enough data tables to properly handle the added flow in some instances (especially WOT/full load scenarios).

Therefore best to get tuned. A Cat-back exhaust doesn't change the flow characteristics beyond what OEM ECU can handle as the OEM cat is still present. But once you go DP (aka Turbo-back exhaust), it's a whole 'nother ballgame.

subie07

Ok that makes sense. Thanks a lot for your help

mofoSTI