Gas Mileage

[baseball_playa1575]

I have a 1993 Jeep Grand cherokee limited. About 3 weeks ago I changed spark plugs. Before I changed them I was getting 14.4 MPG. Now I am getting 8.8 MPG. Could this be caused by the spark plugs? Or could something else be doin it? Any help would be appreciated.

[bringselpup]

Swap the old ones back in and see if you go back to the former mpg again?

[baseball_playa1575]

I cant put the old ones back in I threw them away because they were so bad.

[msdz]

Always keep the old plugs as back up. I even carry the old ones in my tool box in the back of the vehicle they came out of.

A stupid question, did you gap the plugs correctly? If the plugs are not gapped right or even the wrong plugs altogether they will cause a decrease in MPG and power. .005 can make a slight difference in performance, any notice to a decrease in power? Also double check to make sure wires are on snuggly and you did not cross any of the wires.

[baseball_playa1575]

Well I checked the gap when I put them in and they were fine. I have not noticed any power decreases. Is there anyhting else that would cause a drop of 6 mpg?

[jeepgclwj]

Has your foot gotten heavier since the tune-up?

[msdz]

Numerous things could cause it to drop on MPG, as usual my brain took a walk and hasn't returned yet. Hmmm, tire pressure to low, brake sticking, type of gas you are using, low or no gear oil in differentials(usually has a sound involved with this, like a whine or hum), bad plugs or misfiring(which can include any part of the distributor cap, rotor, plugs and wires.), and possible you switched a plug wire or 2 when changing the plugs?
I would just double check to make sure you did not cross any of the plug wires or maybe even check to make sure you did not accidently knock of or unplug any other connections, especially if you might have the 5.2L, not enough room in the engine compartment to curse a cat without getting hair in your mouth.
Give my brain time to return from the trip it took and more will pop in my head.

[baseball_playa1575]

I also jsut changed rotors and brake pads, now there is this weird noise that is a kinda howl, it sounds like the wind. Could the new rotors have soemthing to do with the gas mileage, I wouldnt think so but who knows.

[msdz]

Possible that when the rotors were changed and new pads were put on the piston in the caliber was not pushed in correctly and causing the caliber to stick a little. I believe you would be able to tell from the smell of the brakes unless you only drive a short distance or maybe a back brake, chance you might not smell it like you would the front.
I myself have pushed the piston in wrong causing it to get wedged and not wanna return right, possible dirt even worked it's way in and causing problems. I would definitely check into the calibers sticking or maybe even the flex(rubber) line going to the caliber.

[fredjacksonsan]

Make sure to change the cap and rotor also. If the plugs were in bad shape, chances are so are the cap and rotor. Also, on a 14 year old vehicle if you've never changed the plug wires, now is the time.

If that doesn't fix it, I'd suspect the O2 sensor. When they fail the mixture gets really rich. Is the inside of your tailpipe wet and greasy? Were your plugs the same? Too rich.