About 4 monthes ago i installed the vibrant header and megan catback exhaust into my cobalt ss. For about 2 monthes after that i was gettin around 23-24 mpg and now all of sudden i barely gettin 20 while gettin all highway miles and not reving it past 2000-2500. My car says 20mpg but it eats up gas like it was 10-15 mpg. Did this happen to any of you guys? or do you know what might be the problem?

P.S. my tires pressure is ok

 

Hmmm... Did you tune the car for it and is your cat clogged?

 

winter cold = less mileage, also:

full exhaust = flooring it more often

at least thats how it is for me.

 

yea i get 20MPG if im lucky now lol and mine is tuned

 

how would putting a header n high flow cat combo get u worse gas mileage. some1 elaborate?

 

i havent tuned it yet. which I am stilling trying to find a decent place to tune at a decent price and how would i check if the cat is clogged?....yea i figured that the cold had something to do with it but its weird that it says 20mph yet im wastin gas like i was drivin a jeep...i dont know if im right but i think the system that reads my mpg is reading it wrong...n by the way i rarely floor it

thats exactly what i want to know to know because ive gotten from alot of people that it is suppose to help the mpg by leting the car breathe more

 

Stop and go traffic? Also, NJ will have shitty gas in the winter too. As for the cat, you'd have to pull the downpipe out and check it out. If it's melted looking or blocked it's gotta be cleared.

 

cant b the traffic because its all highway miles and theres barely any traffic the time i drive..didnt bout the shitty gas eitha...ill see if check that out wit the mechanic b/c i dont really mess with all that...would that explain why it says 20mpg even thought its eating the gas up like it was 10-15mpg?

 

my thoughts on the system that reads the mpg; i think it just takes the average on how and where u drive ur car, whether it'd be on the city or highway. stop signs in every block in residential 'hoods are annoying so are the lights and crazy drivers in the city affects the way u drive even if u dont rev over 2500. but if u do it enough times in one trip, gas mileage is goin to suffer ofcourse because of the stop n go n constant throttle changes. it takes more gas to move a car from a dead stop ofcourse than cruising at a constant speed. i've driven my balt from Tenn. to cali, up and down the cali coast, and all the way back across to NYC. i have observed my mpg many times on those road trips. i even got 31 mpg @ one point crossing WY, NE, IA. much different mpg's while crossing thri the mountains of cali, nevada and utah. certainly worse out here in NYC, where people can't drive to save their ass! literally!!!

 

yeaa i know because i rememba when i did all city drivin i only was getting like 13-14 mpg but when i did start driving mostly on highways it went up to 24-25 even up to january and now that im still doing the same kind of driving i did a month ago it has dropped to 20, which mite b b.c of the cold but the problem is that im wastin gas like if i was only gettin 10-15mpg yet it reads 20mpg

 

Run the tank until it's almost empty, and then reset the mileage counter. Run out a tank and check the old way to see what your average mpg is by dividing the number of miles by the number of gallons you had to fill the car with.

Does the performance seem to be less?

 

good idea...ill be trying that sometime this week...thats another thing I've been trying to notice too and i think the performance does seem to be less

 

I typically average about 29mpg with my full exhaust (CA header, XTC 2.5" de-cat downpipe, ARK N2 cat-back) on my 2.4SS, and its un-tuned. I got it all the way up to 34mpg back in September when I drove down to SC to visit my parents. Keep in mind my car is driven daily, sometimes 100+ miles a day.

 

I can get 40mpg @80mph on the highway with all my mods as I tested it on my trip to the OBX in NC this spring. Tuning goes a long way.

Check your plugs, clean the MAF, and check the cat. Any check engine lights lately?

 

danm u people complain if u get 20mpg per gallon..i should be the one complainin since i get about 13-15mpg..180miles to a full tank of gas...

 

Remove foot from right pedal and and be gentle. It helps out, trust me! Now when I romp on it all week or go racing, those numbers look about right!

 

i have full exhaust, intake and other things and still get easily over 30mpg cruising between 75-80 on the highway.

 

the thing is i dont go that...i barelly pass 3500rpm and just romp it when i enter the highway,i just cruise on highway 80mph

 

i havent had any check engines lights but ill be sure to check all those...props to ur tuning though, gotta get mines tuned like that...i cruise at 60 reving at 2000 on the highway n i only get 20....i just dont get how all these ppls have a full exhaust and intakes as well as other things and still manage to get 30mpg...on top of that i could easily say, by the way my gas gauge moves so quickly, my car is gettin much less than 20mpg

 

headers would actually improve gas mileage, it makes the engine more efficient. thats why it doesnt void the warranty to put on a header

 

thats wha i wud think but comparin how my car's mpg did before it seems like it jus made it worst

 

yea i notice that too

 

Here's what I think everyone's gas mileage problems are.
1. All sorts of mods and no tune = excessive fuel dumpage
2. GM Stage 2 tune and stock tunes suck *****
3. Intakes, exhausts, and "a header" will improve the engines airflow to get better gas mileage, but without dialing it in by tuning you are probably dumping excess fuel.
4. Catyltic converters get clogged easily on these cars and a highflow one is pretty much a must.

As another testiment for my gas milege my girlfriend was driving her Scion xB with its 1.5 liters of VVTi fury behing me on the trip the Outer Banks. She had to stop and get gas when I still had a quarter of a tank left! We filled up at exactly the same place before we left, and have the same size tanks! That's why I love this car. Great gas mileage when I want and 20psi on tap for V8 stomping power. Can't beat that with a stick!