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Gas mileage help? I have a completely stock 2008.5 MS3 with 71k miles on it. Up until about 1 month ago, I was averaging around 240 miles per tank with city driving. For some reason, my mileage has dropped down to 190 per tank. I'm not exactly sure about what's going on right now. I haven't been lead footing it, and I don't even really drive the car all that often anymore (maybe twice a week now). I do have a Cobb AP2 and am going to pick up the Cobb intake, however, the sudden drop in MPG is concerning to me. I was told possibly getting some fuel injector cleaner might help (though I don't know if that would really...help). Any ideas about what might be going on? Thanks guys. |
Has the weather in Cali gotten a lot colder in the past month? Are you running a stage 0 Cobb tune or just using your AP as a monitor? Are you buying your fuel at the same place every time and buying the same grade? Have you checked your tire pressures? Is your air filter clean and all maintenance current? |
How many miles on your plugs? I saw a drop in mileage on my car when they needed to be changed. I also saw more kr as they got older. tapatalk, it sucks |
This is the winter time, they change the ethanol content in fuel which = less mpg regardless. But that being said, check your plugs as well. If you changed tunes this can also effect the MPG. These cars get shit fuel economy in the city in general, but you could have also changed your driving habits (like if you go really short distances all the time, etc). In short, do some digging and report back. |
+1 on changing the plugs. Did the same thing on my Evo and it had a noticeable effect on mileage. Aside from that, has your commute changed at all? Depending on if I'm driving predominantly highway or city, I can see between 230-300 miles per tank. |
O2 sensor could be going bad. |
Wow I didn't know they change gas ethananol content in the winter. Does it say by how much at the pump? It might make sense to check the spark plugs. Just pull them out and snap some pics- you don't even have to replace them just yet. |
Post some driving logs with AFR, accel pedal pos., boost, calc load, intake temp, boost air temp, hpfp actual pressure, injector duty cycle, ignition advance, rpm, LTFT, STFT, WGDC, throttle position, and VVT advance. FWIW, an intake will likely cause your fuel economy to decrease further. |
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I totally didn't know that ethanol content was changed too. Is there a reason for that? |
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plugs may not visually look bad but could still need replacing....you're well past that mileage. |
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The shorter the trip, the worse fuel economy you are going to net in general. IMO the only way to tell something is strange from fuel economy is a longer highway trip. |
So you're driving shorter distances now than you were before? If so then thay causes to gad mileage to drop tremendously. I used to drive 3 miles a day to and from work and would average 10 mpg in my subaru. Now that I travel a little farther I've noticed that my fuel mileage has actually doubled. Short trips kill fuel mileage. |
Thanks for the responses guys. I was reading that replacing the stock plugs with colder plugs...like the NGK or Denzo's. Should I just change them out in preparation for the intake and tune? And yeah, definitely thinking that driving short distances may be the main reason why my mileage is crapping out, but I'll check the plugs tomorrow and report back this weekend. |
You don't need colder plugs with just an intake and a tune. Stick with stock heat range. |
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I found that changing the stock plugs (which had 61,000 miles at that point) to have a profound effect on the mileage. Around town or on the interstate, I saw increases of up to 10%. And I only ever changed to a colder heat range after downpipe and stage 2. |
Hey guys, sorry, totally forgot to update. My gas mileage returned to normal after getting another full tank. I do think that the shorter distances ate up the mileage like crazy. Haven't checked the plugs yet, but am planning to buy some stock ones...from what I've read they are the NGK iridium ones? Also gotta change my oil, not sure if that'll help, but it's a bit dirty. Thanks for the help guys, definitely going to change my plugs and report back with the mileage. |
This is the best spark plug for you. NGK Laser Iridium Spark Plug MZR DISI As far as changing your oil go by mileage, not appearance. Old shitty oil can have a negative impact on mpg. I personally change my oil every 2,500 - 3,000 miles regardless of whether it could go another 1-2k miles. |
I've had this car for 5 years now. The first 2 years, I tried really hard to figure out the best ways to get better city MPG only to realize my attempts were useless. I know trucks which get better city MPG than my car. Doesn't matter what I do and how I drive, you're just not going to break 20MPG in the city with this thing. And if I go ape-shit in the city, I get 18MPG. I'm not going to sweat the difference of 2MPG. Face it guys, this is really truck that goes really fast. |
I've been measuring my MPG for the last 10k miles about and have been getting about 21-23 MPG... mostly city driving. If I am frugal and do some more highway driving, I get 24-26. Changing to the OTS "fuel saver tune" didn't do much for my car even being light on the pedal... I think it all has to do with city/hwy, fuel ethanol content, and spark plugs. My last refill I got 20 MPG and was super stressed out about it, but after a refill on the tank it seems like it's back to normal. This is my first winter with the car and temps here just dropped to 20F at night. I took a trip to Vermont two weeks ago and averaged 30MPG for all highway driving... not even trying. My plugs are NGK and were replaced 2k miles ago. BTW, it is recommended you do the oil change and plugs before your tune so things are fresh... |
I barely went over 200 miles a tank. That was with the cobb AP. Fully bolted with tune I got well over 220. Now with BT on conservative tune I get 250 a tank city/highway. |
When you pick up your new plugs, NGK iridium stock heat range, be sure to check gap. With a tune you will want to gap them down to .026". Even with iridium, these cars are hard on plugs. You are long overdue. |
I found Cobb's OTS tunes to be terrible in regard to MPG. My mpg went down noticeably when I started using both the stage 0 and stage 1 maps until I could get an actual tune |
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Replace your fuel filter too if you havent done that |
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This post is timely because it JUST happened to me. Winter time in VA, 2009 with ~85k miles on it. Always 240ish per tank, just recently had 190ish on the past couple. I just had my oil changed, and it seems to be tracking towards 240 now. I was at over 6k interval (bad, I know), so I'm guessing it was getting a bit sludgy in there. |
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This thread has helped a lot, I think its time to swap my plugs lol |
Huge difference in highway and city for me. City i usually get around 17 mpg. On the highway at 60 mph I can sometimes touch 30 mpg. Try the AP real-time mpg monitor. Hit WOT in 2nd and have a laugh. my wrx was exactly the same, just the nature of turbocharged cars i'd say... |
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Hey guys, here's an update. So I replaced the spark plugs and installed a Cobb intake. Also installed the OTS stage 1 map. So far (with fingers crossed) things are looking promising. A little under half a tank and I'm at around 179 miles whereas usually I'd be around 1/3 tank left with that mileage with driving mixed city and freeway. I know it's not very accurate, and we'll see how that one goes. I've also been having fun with doing more WOT and am pleasantly surprised. Then again, I'm a noob at this so I'm sure anything would be fun over stock. |
FWIW - I just recently went threw the process of putting my tune back to stock as I thought that would help my MPG. HOWEVER - I actually LOST mpg so today I put my COBB stage 1 tune back in there. Time will tell if I gain Mileage again. I was getting between 25-27 with the cobb stage 1 When I went back to stock It dropped to 22-25 mpg. That's with gentle driving lol Just food for thought |
I'd start with the basics: -Clean or replace all filters (air/fuel/oil/etc) -Replace plugs -Clean & re-calibrate MAF Aside from that might be time to do some data logging to really find the cause. Could be a ton of things but basic maintenance is usually a good starting point. |
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*Edit, never mind, I see you changed the plugs already. sorry... |
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