Upgrades cause poor gas mileage

OK, I have a 2004 Pontiac Grand AM SE1, 3.4 liter

I recently added a K&N filter to it, New wires (racing wires) and new plugs (high performance plugs) to my car. I have since put in 3 tanks of gas since adding these items....... Now I expected my mileage to go down with the racing parts added BUT.....

I went from getting 485KM to a tank of gas to getting 300KM a tank. That is a HUGE difference, I don't see that these items did that much damage to my fuel economy but what else can I think.

Anyone have any idea's or run into the same thing?


For my American friends.....
Was between 9 and 11 L/100KM and is now 15
or
Was between 24 and 29 MPG and is now 18.7

Based on your description of the problem I really can't understand why your fuel mileage has gone down so far. The K&N and the wires and plugs should not decrease the mileage but improve it. You have not increased horsepower or performance enough to warrant this much of a decrease in fuel mileage. If you had installed a turbo yes but not just improving air flow and ignition.

You may want to get the computer scanned to see what is going on while you are driving. Even though the CEL is not on you may find a problem with an O2 or air intake temp sensor that is causing the issue.

Hmmmmmmm, I wonder now if somethign got knocked off when I put them in....... Thanks, I will look into that.

So, I looked at them all..... nothing was unplugged or loose either. but I took them all off and put them all back on just incase.....

Still no idea why the poor mileage.

lead feet ? maybe....

IF you bought Bosch plugs, there's half your problem. The multi-electrode +2 and +4 Bosch plugs are gimmicky at best, I think AC Delco Iridiums/platinums are a much better choice.

lead feet ? maybe....

lol, my driving style affects my milage greatly :)

Although lately it seems like my GA has lost power almost.. not its normal self .. soon enough, fuel injection cleaned, trans fluid swapped w/ new filter.. new plugs/wires.. for some basic tune ups =p

Ill probly keep tabs on this thread if it has something to do with plugs/wires =o

Two thumbs up on the AC Delco Iridiums! Last year about this time, I replaced my Rapid fires with the AC Delco Iridiums, and my MPG accually went back up.
My pos has 127k miles and I still get around 22-25mpg in the city/lead footin it. Over 30mpg on highways.

I actually used NGK Iridium IV, I was told to only use NGK in my car..... the air filter is a K&N and the wires are MSD 8.5 Super Conductor.

And yes I also have a lead foot, but no more than I did the past 2 years I have owned this car........

i kinda have same prob. i been used to getting 320miles on a tank and now i get 250miles on a 30gallon tank. just today my gas gauge moved about 1/8 tank and i only drive for about 50 miles. only think ive done is add a intake; and i swapped back to stock a few days ago and still hasn't helped. should my computer be configured to the size rims i have? i mean does it make that big of a different. i got like 28mpg thsi summer when i had them now im down to 20mpg on a 4 cyl. its crazy

I am wondering if I disconnect the battery, leave it off for a bit then hook it back up and force the computer to reset itself what that will do.........

actually the newer GA's dont reset there code by just disconnecting the battery thats a thing of the past now you have to have the brain reset by a dealer and they have a 10yr patent on it so it turns out to be a real pain. I found this out on my 96` grand am i replaced the speedo meter and could'nt get the cpu to reset to accept the new speedo meter and allow the car to start. I tryed everything from renting a code reader to disconnecting the battery. I finally had to take it to a dealer and they charged me $45 and it took them about 2mins total. What a way to treat your customers (hurray for GM).

Maybe you guys need to clean you TB's and see if that dont help. Maybe try some Injector cleaner, lik Lucas oil. Those all seem pretty big drops in mpg.

The rim size might effect MPg if the total tire hight is taller than the original size. Most of the time just because you hav bigger rims theirs just a lower profiled tire so the total hight is the same. But Werm9, thats something you'll hav to measure.

I still get great milage, unless I'm racing on it, and even then it still gets 20-22mpg(my tank is only 12gal) Keeping the oil fresh and clean will help mpg. A clean engine may even effect mpg.