Just picked up a 97 gt. Issues?

Hey everyone! I'm new to subarus and the forum. I got a clean 97 gt for $3600, 170k. First trip I took was about 60 miles highway, and I got about 28mpg. Since then I have done an oil change, new air filter, and new tires. I also opened up the airbox a little bit. I am now getting about 17mpg. What could cause it to drop so quickly? Any ideas of where I should start looking? MAF? Oxygen sensor?

 

Thanks!

What do you mean you opened the air box a little? If your driving with it open you will suck hot air from your engine and that will make the gas mileage and power drop.

^ True that. Air boxes are designed a certain way for a reason, if they are ment to be closed than they are ment to be closed. Yeah it does make the engine a little more vocal but definitely not worth the bad gas mileage!

It's something I've done to my cars for years, just cutting the plastic on the airbox below the filter. It's like putting an intake on, just let's air flow through the filter easier. The box is closed and all the air still passes through the filter.

you would have to take a pic. worth 3000 words in your case

only 3000 words. yeah

i'm not a betting man, but i bet that's what did it. only the pics will tell, but if you just changed the oil, filter, and tires, survey seems to say the hole you put in the box haha

Ill post pictures this afternoon. Thanks guys!

get some aluminum tubing the flexable kind it looks very thin and has ring like design u can find it at a hardware store, cut a hole in the bottom of your air bow below the filter and run the tubing in front of your wheel well to pick up some cold air! but dont put it where it can suck dirt!

Fix the air box with another one from the junkyard. Just take the silencer out of the fender. This will allow it to breath a little better and still get cool air from inside the fender. Hot air is your enemy!!!

Thats pretty much what I did, plus enlarging the intake hole about 1/2" all the way around.. Can't get pics up until tomorrow, my girl has the camera. I stopped by the junkyard today, all I found was 2.2 intakes, everything else was picked clean. Would a 2.2 intake work? It looks a tiny bit different.

Are you comparing a 60 mile highway trip to another 60 mile highway trip? I get 28 mpg, all highway, but only 18 when the majority of the tank is back and forth to work.

 

The new tires may have a higher rolling resistance, too.

Okay,

Do you have any idea how much time and money is spent on the R&D of a vehicle? Did you ever stop and think that someone at the factory may have spent more than an hour designing and testing the air box to make sure it performed the best it could under most circumstances encountered buy the average and not so average driver?

 

Why people think they know more about making something work better than the people that designed and built it...I'll never understand.

Believe me when I say that every option was explored in the design of that air box. I worked in R&D for a large manufacturer of motorized equipment. I know a little about what goes into a product before it is released.

 

When in doubt, return to stock. Bet the mpg you had will come back.

correct ! we just want to get some kind of a comprimise between mpg and bhp i have seen alot of performance and minimal mpg drop on japan models right hand drive dy unristricting the air flow and increasing spark.

he did the "swiss cheese mod" to the factory airbox.

hey there is nothing wrong with that haha. I actually did this to my car and I was getting better gas mileage then before

that also wears out and dirtys your air filter fasta

yeah i know but my snorkel was destroyed in an accident so I had no choice but to remove, and I havent seen a reason to replace it yet

i get WAY different mileage in town then I do on the freeway. Highway driving I get around 30-32mpg, in town, I seem to get around 20ish... i have 187k on the clock.

I never have gotten better then 18 mpg and thats on the highway. The worst gas mileage I have ever gotten was 6 mpg in town (driving it like a grandma on church day).

I normally get 21-23 mpg with driving around town. I drive 5 miles on the highway to get to town. On the highway I get 24-25 mpg, I think it is because I'm always going at least 70 so the engine runs to high for the close to 30 mpg.

I've been getting horrible gas mile since I purchased the car. My purchase was partly because of the so-called good has mileage.

 

I managed for the first time in 1.5 years of ownership, and ~13,000 miles driven to get 24 mpg (cruise control set at 65mph for a nearly non-stop 200 mile stretch). I typically get ~19mpg highway and 14mpg city. Anytime the AWD kicks in it drops a ton. Deep in the DC snow blizzard I averaged ~9mpg over a 300 mile period of three days covering the storm. Even in heavy rain it drops a bit. Haven't evaluated it exactly like I have at other times, but I'd put it down around 15mpg in the rain.

 

The cause....well I still haven't figured it out yet. Only thing I've found over extensive reading of a few forums and various attempts to diagnose...LGTs just are not consistent with their MPG. I part think this may be related to why head gaskets are prone to fail, but also at different mileage.

 

I've done many of the basic things to help the mileage. Everything from cleanign the airbox, replacing the air filter, fuel filter, clean or replace the various sensors and valves (most anyway not all of them). At no time did anything ever come up on the OBDII either. I will say I did do two things that I did see a slight improvement. One was to actually clean out the tail pipe. The other was using premium fuel. But even with those changes, overall gain was on average 1.5mpg.

 

So the one thing I'm still thinking that might be the cause is something in the exhaust system that is restricting flow or is slowing engine issue that has not tripped an OBDII code (like decreased air compression). I'm leaning toward Catalytic Converter. Still working things out.

 

I would as others have mentioned, return the airbox to prior condition (no holes) along with any other changes. Also consider that sometimes you get an outlier reading mpg that's high if you say drove a distance at a slower speed...like 45mph over 100 miles without many stops. I did once get a 30mpg reading due to this, but I was only doing 30mph +/- but not in a city driving mode. It was also only over 40 miles.

 

Bottomline, don't assume anything, be thorough in your evaluation and problem solving....it might take a while.

When I first got my 97 LGT with ~170kmi it got great mileage - 24 around town, including some highway and around 28-30 doing the speed limit on all-highway trips. After a year or so I noticed it drop off by around 4 mpg, but couldn't figure out why...until the brake caliper that was dragging seized enough to make it painully noticeable - it was hot when I put my hand a few inches away. After I replaced all four with reman's the issue resolved itself.

 

I also noticed better mileage before replacing my failing EGR vacuum solenoid (had P0400 EGR Malfunction.) As soon as the EGR was working properly, my mileage went down about 1mpg.

 

If the compression is good and nothing is leaking (valves seating properly, etc,) then things start getting tricky. If you've still got the original cat, there's a very strong possibility that it could be restricting flow.

same thing with the brakes, had the car lifted just free spinning the wheels felt alot of resistance, going to change them out pretty soon get a bit more mileage and power back

its true that the pads always touch the rotors right? my dad thinks they get pulled away from the rotor when you let off the brakes. please tell me he is wrong