shvc1991

Recently I've noticed a HUGE difference in gas mileage. I mean I'm getting 15mpg city and about 18 highway. I never rev more than 3K RPMs. I used to get 18 city and about 22-23 highway.

I noticed this significant drop only after I installed my audio system. I really have no idea what's going on. Any ideas?

jcat_350

if it's after you installed your system, it's probably from hauling the extra weight of the subs/amp in your trunk.

seriously, i have an 01 gs3 that normally gets ~21mpg with about 65% city and 35% highway, and i do rev over 3k semi-often. When i first got the car i had sold my ML430 which had my system in it, and just by having my 2 12" JL w3's in the box (they weigh a combined 80lbs give or take a few) my mpg dropped to about 18 or 19.

shvc1991

Damn. That sucks.... Guess I should build a custom box to shave some pounds.

jcat_350

im not necessarily saying thats definitely the cause, it could be a dirty maf or TB but i will say expect to lose 1-2 mpg with the extra weight.

shvc1991

I'm going to try to get some MAF cleaner. TB would do it to, huh? Thanks.

I might as well just go with the custom box anyhow. I have like 120lbs worth of **** in the trunk.

jcat_350

haha, my dude the list is endless. any acceleration issues/mpg issues could be any combo of:

-dirty maf
-dirty tb
-dirty air filter
-dirty fuel filter
-bad spark plugs (would throw CEL)
-bad ign. coil (would throw cel)
-low tire pressure (even 1 tire way down will reduce mpg by about 5)
-bad cats


and a host of other things i'm probably forgetting.

shvc1991

I've had previous problems with one of the cats.... I might check it out again.

GSteg

iTrader: (15)

previous problems? as in it's already fixed?

Your cat is fine if you're not throwing any code. OBDII is sensitive when it comes to O2 reading. If you have problems with the cat, your CEL would be showing up by now. I would definitely get the car checked for the basic stuff. Perhaps increase tire pressure a bit if you dont mind a slightly stiffer ride. I was getting 20mpg with the OEM 32psi rating. Bumped it up to 36psi and got ~22mpg. Worth the trade off for me since I'm on springs anyways. Minus whale sacrafice ride comfort

shvc1991

Found the problem... Rear right tire was only getting 29psi... Got all my tires to 35. Fun. I like the slightly stiffer ride anyhow as I'm pretty used to driving an e46 330Ci with the performance package.

MJImport

iTrader: (1)

I usually run mine near 38 psi, I like the ride, and I always manage to wear out the outsides of my tires so a higher pressure helps to even out the wear.

As far as weight goes, shaving 100 lbs will drop your mgp by less than 1 mpg (I was a weight engineer at a major OEM for a few years ) You get much more bang for your buck from aero improvements than from weight reduction.

jcat_350

wow, you guys are running your tires 35 and up? i have the OEM 16s and i run them at exactly 30 or 32. I know they can go higher but i just follow spec, i'm surprised you guys are willing to let go of some comfort for an extra 2mpg...

shvc1991

If that's the case.... I need to save up for a Wald kit. I likes it. I also need to get rid of my OEM spoiler.... It rattles too much when the music comes on.

I actually like the bumpier ride. I started favoring it once I started driving around in an e46 330Ci. I'm a 17 year old so stiff doesn't really bother me and saving gas is also a plus as I don't exactly make too much money.

pingu

You should also take into consideration that you may get uneven tire wear if you increase the PSI in the tires.

shvc1991

Meh.... That's fine by me. I just got some Toyo Versados and they're covered under warranty very well. If they ever wear out, they will be replaced no questions asked for the rest of my life.

I'm sticking some winter tires on pretty soon anyhow. Almost time for the cold to come in.

jcat_350

might i recommend fuzion HRi's 75 a tire, made by bf goodrich and theyre supposed to last 40k miles. All season tread but aggressive enough so you dont lose too much handling. A bit noisy on concrete highways but i'm looking forward to the snow because i think they'll grip just fine.