TLUZLS1

iTrader: (6)

I monitor my gas mileage VERY closely and I have noticed a steady decline. I travel back and forth form home and college which is about ~190 miles away. I used to be able to make it with a little under half a tank, not i make it in a little under 3/4 of a tank. Also in the city I used to make it about 70 miles to the 1/4 tank line on the gauge, now i can only go about 40-50 miles to the mark. When i calculate my milegage at the pump I notice it has fallen off as well, over 2-3 mpg.

So here is what i've done since i started losing mpg:
*New air filter
*FRA mod
*Semi-new wix fuel filter (about 20k mile on it maybe less)
*New o2 sensors
*Fuel treatments
*New plugs (ngk tr55s)
*MSD wires
*37 psi in the tires
*Fairly new clutch (~10k miles on it)

So what should i do about it? I don't want to sea foam it either.

My car has LT's, tsp catted-y, hooker catback, e-cutout, lid, and self p&p TB. Oh and it's been tuned (on a dyno). Car has 97k miles on it. Also, in the past few months my car will have a little trouble starting, regardless if the engine or outside temp is cold. I can crank on it for about 5 seconds and nothing, then when i crank again it fires right up. And it doesn't do it all the time.

So please help!

SparkyJJO

iTrader: (11)

Why don't you want to seafoam it?

Also, I don't know about Texas, but during the winter months they reformulate the gas and it always results in lost mpg. They can't seem to leave well enough alone.

TLUZLS1

iTrader: (6)

Well with that many miles on it i just don't want to risk loosening anything up in there that might result in engine damage. I've just heard some bad stories...

The decline has been since around last spring so it hasn't just been a recent thing.

LS1crazy01

iTrader: (14)

What kind of O2 sensors did you put on it? I would just stick with OEM ones. and as far as it not starting right away, have you tested your battery? Maybe check to make sure all the plug wires are "snapped" on. Did you check the gap on your plugs before you installed them?

LS1crazy01

iTrader: (14)

And what kind of "fuel treatment" did you do?

TLUZLS1

iTrader: (6)

^^^Bosch 13111. And yeah i made extra sure i had all the plug wires on good, and yeah i checked the plugs, they were all at ~.050. Im almost positive my battery is fine, it's an optima red top. I can have the key on run and listen to music for a couple hours and it's fine. I can check it today at work though (o'reillys...). I have tried a couple of the chevron techron additives, they are supposed to be one of the best.

LS1crazy01

iTrader: (14)

My car gets gunkd up to the point where it miss fires somtimes and hesitates and I through the whole big bottle of lucas thats supposed to treat 100 gallons in and then fill the tank and run it dry and it clears up everytime and my mpg picks up from 18-20 to 21-22.

rich Z

3 things to do. Have the pcm checked the codes. Seafoam treatment and if the mpg still sucks then a professional fuel injection cleaning. The kind where pressurized cleaner is run through the fuel rail.

TLUZLS1

iTrader: (6)

^^^I might try the professional fuel injector flush. Do i need to check the codes even though my light isn't on?

And crazyls1, isn't that a bad idea to put all that lucas in there? I know which stuff you are talkin about though.

Is there any way to check/test my fuel pressure? With the slow starts i think my fuel pump might be on it's way out, plus my car has never ran that strong for an ls1.

SparkyJJO

iTrader: (11)

There is a schrader (sp?) valve under the hood to test fuel pressure. If it is ok when the car is running but it drops off when the car is off it could also be the fuel pressure regulator. My car went from starting a little hard at times to taking 5 tries to get started and keep running. Pressure regulator was bad and not only was dropping pressure off but was letting fuel into the vacuum lines.

fccs

iTrader: (26)

It seriously may be something simple like because of winter months, alot of states use gas that has **** in for winter. Everyone will normally get 1-3mpg LESS during the winter months of november-march because of the gas used compared to the summer. I personally would wait until about april and see if the mpg raises again.

TLUZLS1

iTrader: (6)

Okay cool ill look into it.
Well my mileage has steadily for about a year now, so even in the summer my mileage was bad.

wssix99

iTrader: (5)

You can't monitor mileage using the gas gague. You need to fill up the car, take your trip, and then fill it up again to get the true usage. The performance of the gague is non-linear, so at certain points of filling, a small amount of gas can make a bigger impact on the needle position.

fccs

iTrader: (26)

Ah, Well like others said, id check ur tune out or have it redone, I doubt you need to sea foam I wouldn't bother with that but make sure sensors are working and all. I have a 98 with 90k miles and I avg about 20/30 15/25 when driving like a mad man. I never sea foamed my car or had it tuned yet, even after the headers. Something cant be right especially since ur car is 4years newer then mine. You never really mentioned how much mpg as a average your getting though? Say for example if its like 12-15mpg city and maybe around 25 highway, then that isnt that off it would all depend on your driving. But if your around the 10mpg and barely 20 on the highway then I would say something is wrong.

TLUZLS1

iTrader: (6)

Oh no believe me i know. My driving routine is just so consistent i can get an idea how how much gas i am using. I always fill up at the same station, and then drive about 190 miles to school. Or drive to and from work and see how much iv'e used in the same amount of miles and on the same part of the gauge. I never fill up just halfway or just put in a splash, i always fill it to the top and then calculate.
I used to get right at 18 in the city, and about 26-27 on the highway. Now i get about 15 in the city, and about 22-23 on the highway. So it has definitely fallen off, and my driving habits haven't changed. Oh and the tune was already re-done, and it was by a very reputable place (g-force).

Another thing, it seems no matter how hard i drive it, my fuel consumption is the same. I can skip gears and keep it below 2k rpms the whole tank and get same mileage when i go to the track or speed around...

Im just really confused...

fccs

iTrader: (26)

and you say this has been doing this mileage even last summer? like around july and august even?

TLUZLS1

iTrader: (6)

Yeah even before that actually. Something is really wrong and i just cant seem to track it down.

wssix99

iTrader: (5)

What brand of gas do you buy?

TLUZLS1

iTrader: (6)

Only exxon

wssix99

iTrader: (5)

Carbon deposits may be a part of it, but I doubt that would account for all of your mileage loss. I did a CarbonClean treatment on my car (similar effect as a SeaFoam treatment) and I got 3-4 mpg back.

After going through that, I only fill up with top tier gas now: http://www.toptiergas.com/ (ExxonMobil still isn't with "the program")