Bad mileage, not sure what

[siether]

I've lately been getting poor fuel mileage (300km / 190mi per tank) used to get 400-410, and i'm not sure why. I've change my air filter, changed my oil to full synthetic from semi, just changed my fuel filter (which was pretty dirty). I haven't changed the plugs yet cuz I'm not sure which would be the best ones. One thing I have noticed is that when I step on the gas it bogs for a sec then goes. Any sugestion would be great.

[AlbinoMonkeyRat]

perhaps the type of oil is what's hurting it. usually, once a car is "used to" a certain kind of oil, it operates more efficiently on that type. However, that shouldn't account for a huge change in the mileage.

There are also other things you can do:
-fuel system cleaner (the type you pour into the gas)
-tune up
-clean the butterfly valve in the throttle body. if it gets too dirty, the valve flaps will stick open or closed. if they stick open, you will run lean, if they stick closed, you'll choke it (no air). (if you have a CAI or a WAI, you already know where this is...if you don't, it will be a bitch to get to...)

also (joke) maybe they switched to winter blend gas already in Canada...

[Redog]

AC Delco plug or AC Delco rapid fires. are the best for a GM car

Change the plugs, you did everything else

[siether]

I know it can't be the oil because i was already haviing bad mileage before I changed it. But i'll check out the butterly valve to see if it's sticking.

[SweetNLow]

Originally Posted by AlbinoMonkeyRat

perhaps the type of oil is what's hurting it. usually, once a car is "used to" a certain kind of oil, it operates more efficiently on that type.

dude your so wrong its not even funny.

the type of oil doesnt affect your milage at all. different weights of oil have to do with there viscosity (sp) when cold.



anyways. im gonna suggest that you possibly have a bad O2 sensor or perhaps you catalytic converter is getting clogged.

[AlbinoMonkeyRat]

you leave out the part where I KNOW it's not the answer...lol

[siether]

If I had a bad O2 sensor wouldn't it throw any codes? Never had a check engine light come on yet (knock on wood). And I take it threre's no way to unclog a cat converter other than changing it out.

[SweetNLow]

only way to fix the cat is to get a new one.

do you hear a rattling sound from underneath your car at all?

[super white alero1]

Get your intake cleaned, go to a shop that offers BG-44K intake cleaner. 3 part kit. Have your injectors cleaned thru the fuel rail not thru the gas tank, change your fuel filter, change your S.P. buy some carb cleaner and hose down both the O2S (oxygen sensor) and AFS (Air Fuel sensor). Total cost should be about
$14.36 = $3.59 X 4 (S.P)
~$10.00 (fuel filter)
~$150.00-$225.00 (Engine Treatment)
~$5.00 (PCV valve)
~$5.00 (carb cleaner)
Average price for all this is about $200.00 and that should improve your gas mileage.

[battistoni21]

id go with NGK iridium plugs.....

the lucas fuel cleaner worked decently when i used it....

also it wouldn't hurt to try some seafoam either....

[natedawg9640]

all i know is that i should consider this too... cause i have a 2.4 and it's a stretch to get 350 miles on a tank... it used to go well over 400...

[siether]

What is seafoam? And what is it used for, sorry to sound dumb but never heard of it.

[billytheman1188]

Thats for sweetnlow.....lol hahaha

[siether]

I finally found a place that sold seafoam out here. I put half in the tank and then I let it slowly suck up the rest through the brake booster line the shut off the motor for 5min. I also changed the oil before that. When I started it back up I let run for a few minutes, I right away noticed that it was idling smoother running quieter. I used to be getting about 35-40km before my needle on my gas would move from the full mark and today it didn't move until around 65km. I think seafoam is my new best friend, now I don't need to spend big bucks @ the dealership to get my injectors flushed.