Bad Gas Mileage [Merged 9-6]

[99GST]

I am still getting some pretty bad gas mileage.

I am only getting about 19.7 mpg with mostly city driving shifting at 4k.
I have already replaced my front O2 sensor and am looking to replace the fuel filter.

I have a 99gst with about 55k miles on it. Should my fuel filter already be bad?

What else should I check or change? I have NKG plugs and Accel wires are on the way.

Thanks,
Nathan

 

[GSX93DSM]

Fist of all put everything back the way it was. If your running 20psi like that with no intercooler You need to do a boost leak test. Keep it at 14psi. I do not know what your mods are. Possibly a wastegate problem. I would start with the boost leak test.

 

[kottyking]

Yea guy your gonna wanna leave the intercooler piping the way it is. No offense but who swapped the turbo on there?

 

[grnchevyz]

OK This just really pissed me off...what? Are we not HELPFUL enough for your liking that you have to double thread the same problem? I'm pretty sure that with the steps I told you to take and the new reply I put on there we would have been 99% certain of the problem...now, well, you're on your own.


Sorry If I seem harsh/pricky but this really pissed me off like me and the others weren't guiding you in the right direction...PLUS not to mention you changed the title to something COMPLETELY irrelevant to your issue.

Oh yeah and FYI here is his original thread

http://www.dsmtuners.com/forums/newbie-forum/312234-cant-run-over-14-psi-adjust-psi.html

 

[clockworktoy]

Wait you have a 14b in a 2g with the stock bov? I think i just solved your problem bud.

 

[SD99GST]

Wait you have a 14b in a 2g with the stock bov? I think i just solved your problem bud.

I agree, time to go shopping for a BOV. From what I know about the stock 2G BOV is that it cant hold more than stock boost pressure, someone correct me if Im wrong.

 

[grnchevyz]

I agree, time to go shopping for a BOV. From what I know about the stock 2G BOV is that it cant hold more than stock boost pressure, someone correct me if Im wrong.

the stock bov will hold 1bar, anything above that is a coin toss. change the bov that should take care of it.

as far as I know you need an adapter for a 1g bov, unfortunately.

 

[Burtismaximus]

What makes me mad about this is that i can barely understand what he is trying to say because he cant read forum rules and write complete sentinces ya know.

 

[96turbo_gst_fwd]

you must not read very well youself because I understood it just fine but i think he did maybe miss a period or two. Way to be buddy way to be.

 

[Spartan66]

Ok i searched and I came up with bad MPG for turbos and AWD but ive got a GS none turbo and thought my problem may be slightly different. So Im coming from owning a Z28 camaro and a 98 chevy blazer both of which didnt get great mileage especially the blazer but the Camaro seems to have gotten about the same mpg as my Eclipse.

I recently got a full tank (i believe that to be what 15.9 gallons?) and i went about 200 miles before i hit E. I did about half of that on the hwy going about 55-60 and the rest were city miles. I also live up a plateau and drive up and down that plateau to go to and from work which isnt far away at all, maybe 5 or 6 miles but i work 5 days a week and then theres my liesure driving etc but i dont have a heavy foot at all ive maybe gotten on it once or twice.

when i bought the car it had a cracked header which i replaced last weekend along with spark plugs, wires and an oil change (before I filled my tank before i did all this so thats probably partially why i got the mpg i got which before the sparkplugs etc. was like 9mpg.) Anyway currently my intake filter housing was missing all the clamps and was partially open so as a cheap easy fix until i could buy a new cold air intake i just ducked taped it so that it was "sealed" however all the holes in the filter housing dont really meet up with where they look like they should.

Finally i got my emissions tested recently and when i went in at first they sent me home because my idle was higher than 1100 in park so i went home and set it for about 700-800 which i was told to be about stock idle speed went back and passed. However while driving at about 30-40mpg or if i want to maintain speed the car idles at 2k or more and if i want to make it up the hill to get home and maintain 35mph i have to give it a decent amout of gas. My gas pedal is VERY stiff and i just cant seem to maintain speed at anything lower than 2000 rpms. Is this normal or could i be experiencing some problems?

Thanks for reading my long post , but it figured some explaination was inorder to understand what ive been experiencing. I apprciate your time and help.

 

[DSM1G90]

My gas pedal is VERY stiff and i just cant seem to maintain speed at anything lower than 2000 rpms.

With the latter part of your descript, you've got an Automatic -saying that you were in "park."

Throttle pedal shouldn't be at all stiff. I would check your t-cables for free play, and that is to disconnect the cable from the throttle plate connection and see if the cable can move freely by hand. If you got a cruise control box that the cable goes into, the cable from the pedal goes into this box and controls the other cable that connects to the throttle plate.

Sorry to say, but hill driving does soak up on the gas since gravity is our worst enemy in trying to maintain the best MPG we can get. And with automatics, that multiplies the problem.

Now, if you have an automatic and doing hill driving, have the "PWR/ECO" switch in "PWR" - for this will help the tranny have better shift points. But, when you get on the flat, then switch over to "ECO" so the tranny can take advantage of steady driving.

You did the one half of the tune-up, but did you get a chance to do the other half to ensre that the timing is at the correct 5* BDTC setting?

Plus, what motor is in the rig? the 1.8L, or the 2.0 DOHC since Eclipse GS came with both motor options?

'bout all I can say for now on your situation.... Good luck - DSM

 

[Spartan66]

Ive got cruise control and an auto tranny. As for the tune i have yet to do anything other than the oil and plugs/wires. Im runnin the 2.0L DOHC. Car has 171k engine has 51k.

 

[GalantGreg]

I would say you replace the fuel pump, fuel filter and air filter. Sounds like the engine has been changed, but probably not the those. 171k on a fuel filter and fuel pump, and it is not going to perform like it used to. I would also run a can of seafom through the intake to clean out the injectors and valves. You only need 1/3 of a pint. I would also run a can through the gas tank. And a can in your oil about 200 miles before your next oil change.

 

[19Eclipse90]

The only way you will ever be able to put in 15.9 gallons of gas is if your tank has been drained nearly dry. It is different for each car, but on my car, I hit E as soon as 11 or so gallons and as late as 12.5 gallons have been used. The most I've ever had to put in my car to fill up was just above 13 gallons and that, IMO, was pushing the limits.

The correct way to gauge MPG is to completely fill up your tank and mark the mileage or set your tripometer. Then drive until you fill up again. You then divide the miles driven by the number of gallons needed to fill your tank up the second time. You are neither putting in nor using 15.9 gallons of gasoline.

 

[DSM1G90]

(was wondering on that amount of fuel in the tank since the tank specs is the 15.9gal..empty)

But, just remember - an auto tranny will not get you the best over a manual any day of the week. Thus, hopefully we can get you into the low to mid 20mpg range after all is done.

 

[MaxGdsm]

i would hope you can get better than low 20mpg after a tuneup. I have a few mods on my awd car with wider sticky tires and highway driving i got 27mpg and around 18 in town.

When putting the seafoam in the oil do you guys recommend drivng around alot with it in there? I was told to put it in the car and let it idle for about 10 minutes then run it for about 3-5 minutes at around 3k rpm. then drain it and go. I filled the car back up with oil ran it again and drained that too just in case. I am overly cautious but im just curious what others recommend with the seafoam and similar products.

 

[Spartan66]

Hey thanks for all the help guys i really appriciate this as i bought this car for more of a gas saver than anything but i cant just leave any car ive ever bought stock so i figured id tool around but not until its running tip top.

So fuel pump and filter and i planned on getting an intake kit anyway. I will also take note of the seafoam before my next oil change.

So if my math is right, if E is around 11-12.5 gallons for you im getting roughly what 16-18mpg? If so thats actually about the same as my big V8 Camaro ... So im looking forward to puting your advice to good use, thanks again.

My final question is will a new fuel pump/filter/intake/seafoam and fixing the stiff gas pedal fix my lack of power problem and lower my cruising rpm from doing 35-45mph at or above 2k to about 1,500 rpm? Or will it just improve my mpg or both? Sorry if i sound like a total idiot asking all these questions but with most of my previous vehicles ive expected poor gas mileage and they all had any where from 160 to 285hp and alot of torque

 

[GalantGreg]

My final question is will a new fuel pump/filter/intake/seafoam and fixing the stiff gas pedal fix my lack of power problem and lower my cruising rpm from doing 35-45mph at or above 2k to about 1,500 rpm? Or will it just improve my mpg or both? Sorry if i sound like a total idiot asking all these questions but with most of my previous vehicles ive expected poor gas mileage and they all had any where from 160 to 285hp and alot of torque

Changing the fuel pump and fuel filter will help your gas mileage. If your current fuel pump is under duress, that means the motor is being starved for fuel. Which will decrease mileage significantly. The seafoam in the intake by a vaccum line cleans the carbon from the valves in the head. Clean valves helps increase power and gas mileage. The Seafoam in the crank case before you change your oil acts as a detergent and cleans any gunk or build up on cylinder walls and your pistons. This helps increase power and gas mileage as well. Seafom in the fuel tank cleans the fuel system and the injectors. I recommend doing the fuel system before you change the fuel pump and filter.

If your gas pedal is sticking, get in there and check and make sure it is not being caugh by the carpet. If not, check behind the pedal, and check the throttle cable under the hood and make sure it isn't bunched up or something.

 

[Spartan66]

Its not the carpet im sure of that. Ill check everything out under the hood.

 

[tsi1991awd]

Hey man I'm kind of in the same boat as you. I have a 91 TSi AWD, I changed the plugs and fuel filter and noticed a slight increase in mileage. Dumbass me never bothered to check the tire pressure and one day I really looked and my back tires looked flat. Went to fill them up and sure enough they didn't even register on the gauge. Filled them up to about 30psi (I'm in WA too...cold weather needs higher pressure) front tires were at 15psi so I bumped those up to 30 as well.

After that, I went from 18-20mpg to 22-23mpg. Same route everyday, same driving habits, etc. Especially with AWD, your tires should all be the same pressure or else your gas mileage will suffer.

 

[Spartan66]

Yeah i checked the tire pressure and filled them with nitrogen at work. I take good care of my tires because the car came with nice aftermarket rims and Toyo Proxys and those are kinda expensive and i dont want to replace them for a LONG time .

 

[tsi1991awd]

Another thing, if you have a lot of weight in the car, that will eat up gas. Like hauling car parts or lots of luggage or whatever that you could clear out of the car. Might want to check your O2 sensor. Fuel filter especially.

 

[Spartan66]

Yeah, i havent gotten around to replacing the o2 sensor and with the cracked manifold i used to have im sure that didnt help. but ive already got some stuff ordered and ill install it all and let you know how she runs.

 

[MaxGdsm]

good luck and keep us updated, oh and happy halloween!

 

[Spartan66]

Thanks bro, and I added a can of Seafoam to the gas and ran it for a few miles. Probably about 10 or 15. As for adding it to my intake, should i get deep creep or just pour it into the throttle body? Whats the best way to get it through my intake? Also im planning on getting the new fuel pump and filter soon because i read through the troubleshooting section of hanes manual and you guys were right my symptoms and the things they said i should check are the same, so ill look into getting those.

 

[gst96spyderman]

So I'm getting about 22-23 mpg @ 65% highway driving and 35% city. Most of the time I'm pressing the pedal till I hear the turbo spool up. I have a 100% stock gst spyder with 17" chrome rims on 235-45-17 nitto's. Is this about right? 22-23 mpg? I mean, if I'm on the highway, I'm crusing @ 85-100mph 50% of the time. Not asking how can I get better milage. Just if this is typical with my driving?