Factors that affect fuel economy

2000 Grand Am SE, 3.4L V6, 140k.

I commute just under 200km/day to and from work. Initially I could get 3 1/2-4 trips out of a tank, but now I'm lucky if I get 3 at all. No check engine lights or anything have come on, and the air filter doesn't look like it needs to be replaced, but I'm thinking about replacing it anyways. Just wondering what else could affect fuel economy... Spark plugs need to be changed soon, but would they make that much of a difference? Please help! Thanks in advance.

Many things affect fuel mileage. A dirty air filter for one. Even though it doesn't look dirty change it, you might want to try a K&N or similar filter like a Fram Air Hog, more air flow helps performance and can improve fuel mileage. Second, change the spark plugs. Fresh plugs can improve fuel economy. Finally, you may want to change the O2 sensor on the exhaust manifold or downpipe in front of the cat. It tells the computer what how much fuel to allow in based on Oxygen content. A lazy sensor will decrease the fuel mileage and will not necessarily give you a CEL. Try this and see what happens. One final thing, try using a good quality fuel injector cleaner will clean the injectors and better atomize the fuel for increased fuel mileage.

Good Luck!!!

Ya the 99' GT I just got a few weeks ago was geting about 17-18mpg. The plugs were good, but the air filter and oil was nasty. Changed them, threw in some Lucas Oil injector cleaner and it bumped up to 20 mpg. Still wasnt good enough for me.

So I took the air intake off, and looked inside the Intake and it was pitch black with carbon deposits.
Took some good TB cleaner and sprayed it into the intake/TB with it running 4-5 times really good(you hav to throttle up for this, kinda loud too!) , the last tank after this cleaning was 24mpg. So apearently that was my problem with my bad mpg.
Also keeping your oil changed at regular intervals helps big time too.
Just though I'd through in my :2cents:

aye sir, I changed my plugs and got amazing gas mileage, no idea what tho but if I can drive over 100 miles highway and still have half a tank give or take... thats pretty good in my book....

Sweet... Thanks for all the tips!

Now as far as the plugs go, should I attempt changing them myself, or have a service shop do it? I can see that the front three plugs are easily accessible, but the ones on the rear below the ignition coil look to be hard to reach. Any ideas?

Ya they are a Pita :grinyes:

A short extension, a stiff swivle-joint wouldnt hurt , and a good deep well sparkplug socket.
Lots of patients doesnt hurt either :lol:

remember they are in at funky angles and you cant really see much back there, anti sieze on the threads is always a good idea.

Good Luck

I just got the AC Delco Iridium plugs for about $4.90 each (great deal) and I noticed not only a lil more horse power (already had accident heh) but my mileage went way up...

Yea bro like XI said, those plugs in the back are a PITA!! .. good 30 or so mins to do it all for me.... Make sure you have a good enough reach that once you have the new plug in to be able to put ur hand down there and see which way its pointing towards to I guess give you a better idea of how the plug wire is going to be fitted back on... when u put em on they'll do a lil click or snap on...

Make sure that the engine and everything is cooled off before you goto work, dont want any blisters and burns :p ... a box fan layed on top of the engine works good just blowing air down into the bay... that took about 5-10mins to cool everything down for me rather than waiting for it to normally cool down from 200F!! lol

But of course if you dont feel comfortable doing all this, go ahead and see if you can maybe get a friend to do it...(save $$$ :) ) or goto a tune up shop and see what they could do for w/e high price of labor heh...

I have been getting bad mileage with my card since I bought it 4 months ago. I was getting about 375 KM per tank of gas. I calculated(roughly) about 22 MPG. The air filter is brand new, and the oil looked great. So, I changed the plugs to Bosch Platinum 4+. they were about $20 a pair. But I have seen an increase of 25 km per tank. Still pretty crappy from what I think I should be getting. I calculated it at about 25 MPG now. I am going to change the fuel filter next, and I will try the air intake trick that someone else posted above. I will keep you posted.

depending on what engine you hav 25mpg isnt to bad for both city and highway.

THe biggest factor in MPG is ones foot :)
I driv my GT prety hard and get around 24-25 city. Out on the high way 200 miles straight I got 30mpg.
My SE with mods out the wahzoo gets better on highway, but about the same city.
a lot depends on where you get your fuel, octanes and so on.

Just a question about spraying TB cleaner into the intake, does it work better to spray the cleaner into the intake while the car is running or following the directions on the can and just spray it into the intake while the car is off. I tried it the last way and I don't really notice any big change in the MPG.

Remove the throttle body and clean it that way. You can clean it better and this will allow you to clean the back of the throttle plate where the most carbon is located. Remove the idle air control motor and clean it too as it will allow the engine to idle better. Just don't push the pintle when it is out of the car or you can damage it. Also clean the opening in the throttle body where the air goes through from the IAC.

Wow, maybe mine is all carboned up too. The previous owner was 82 years old; I am 51..... the poor GT1 is used to driving like an old lady on a Sunday ride. My nephew is a cop here, and he always tells me I'll get a ticket for driving too slow. Maybe I should clean out my throttle body too. Anyone happen to have a pic of what it looks like, lol ? I know, stupid question..... I don't really know too much about the engine, lol.
Now.. stop laughing at me, lol !!!!

EDIT >> I forgot to add... My car is runnin' like a top; no problems at all. Just wondering if cleaning the throttle body is like a preventative extra measure...

Usually the engine will run very well even if you don't clean the throttle body. As long as the throttle plate can move freely you shouldn't have any issues. The idle air control motor should be cleaned if you notice the idle is slowing down or if it is eratic. This is simple to remove and clean. Located on the side of the throttle body and looks like a small motor. As for the throttle body I am sorry I don't have a picture to post.

Good morning GTP; many thanks.. I'll leave well enough alone; she's runnin' great, lol.. I hope the original poster didn't mind me jumping into his thread.... Thanks again..

Tommy

I got Iradium IX and with crappy ingition electric wires but they are working so much better than platinum 4 or any other crap plugs!

I get about 20mpg and will probably change O2 senson soon!

I'll try what you said also GTP Dad, but I was also wondering if cleaning the intake like xeroinfinity said earlier (with the car running) would clean any more carbon out of the intake then just spraying it into the intake and moving the butterfly.

spraying into the intake while the car is running cleans deaper into the intake plus the valves.
Keeps the TB cleaner from pooling inside and diluting the oil, + fouling out the plugs. That always sucks :grinyes:

For the TB and butterfly, I use an old tooth brush soaked in TB cleaner, And on the Iac.

Hope that helps :)

Good advice xeroinfinity! I usually just remove the throttle body and clean as necessary. I have never had good luck with cleaning them on the car.

Good advice xeroinfinity! I usually just remove the throttle body and clean as necessary. I have never had good luck with cleaning them on the car.

Thankx!
A bent tooth brush works even better :thumbsup:

I hate taking the TB off !
Waste about 25-30mins , all the damn hoses underneeth from that recirculator tube..... :shakehead
I dont even remove the TB for a thermostat change :)
...... try that one :lol: