Miles per gallon has dropped alot...

[jimdigs]

I used to get high 30s to low 40s mpg. Now I get around 26!! Whats up? I believe it has to do with my transmission. It has started to slip lately would this cause the engine to work harder? Thats all I can think of as to why my miles per gallon have dropped off so much. I have not changed the fuel filter in the two years I have owned my 90 festiva. What do you guys think may be going on? She only has 109,000 miles. She does burn oil too. Thanks.

[FestYboy]

i'm assuming the trans is manual seeing as you WERE getting low 40s. the trans slipping shouldn't account for a 40% decrease in MPG. i recomend a new DENSO o2 sensor, plugs/wires, and verify your brakes aren't hanging up. you could also have a clogged airfilter or weak ignition coil (both are easy to remedy, though the coil should be replaced with an after market unit. stockers can be more than $100)

[TominMO]

Checklist:
1. Tuneup parts: plugs, rotor, cap, plug wires, air filter--how recently has all this been done?
2. O2 sensor on the exhaust manifold: replace with Denso unit only
3. Run some fuel system cleaner thru the gas tank.
4. Are rear brakes or bearings dragging?

EDIT: You just beat me Arty!

[FestYboy]

gotta be quick Tom...!

[georgeb]

I used to get high 30s to low 40s mpg. Now I get around 26!! Whats up? I believe it has to do with my transmission. It has started to slip lately would this cause the engine to work harder? Thats all I can think of as to why my miles per gallon have dropped off so much. I have not changed the fuel filter in the two years I have owned my 90 festiva. What do you guys think may be going on? She only has 109,000 miles. She does burn oil too. Thanks.

Auto or stick? Carb or EFI?

[FestYboy]

90 = EFI
40+ mpg = stick

[WmWatt]

You don't say where you're at. Milage in winter in cold climates is always lower.

[FestYboy]

not 15 mpg...

[kartracer46]

not 15 mpg...

I agree, except in the winter some get more idle time warming up, staying warm while parked waiting and other reasons. But 15 mpg is kinda big, that would be a bunch of hrs vs. miles registered to see those numbers.

[Movin]

You have changed the timing belt?..
You can bump the ignition timing a little in the winter.
Run pure gasoline if you can find it..places where
boats and snowmobiles fuel up.
Make sure the winter fuel hasn't plugged your cat converter.
Don't leave the ski rack loaded on the roof !

[jimdigs]

Ok, so I changed the spark plugs and put in a new air filter. That helped some. I am now up to 30mpg. Any more suggestions? Would an O2 sensor do the trick?

[sc72]

Low mpg's

Check post #2 of this thread, Festyboy is helping you get your mpg's back. Have you checked the engine compression.

[FestYboy]

Ok, so I changed the spark plugs and put in a new air filter. That helped some. I am now up to 30mpg. Any more suggestions? Would an O2 sensor do the trick?

if an o2 goes bad, it always goes "hey, it's too lean in here!!!!" or at least that's what the ECU interprets a low voltage signal to be from the o2. so to counteract this percieved lean condition, the ECU starts dumping fuel to the point of peging out its fuel tables. you can test this by using a DVOM and backprobing the o2 harness plug. voltage should swing between .100 and .900 volts with a good o2 sensor. a bad sensor will stay around .1 (or no volts at all).

[TominMO]

if an o2 goes bad, it always goes "hey, it's too lean in here!!!!" or at least that's what the ECU interprets a low voltage signal to be from the o2. so to counteract this percieved lean condition, the ECU starts dumping fuel to the point of peging out its fuel tables. you can test this by using a DVOM and backprobing the o2 harness plug. voltage should swing between .100 and .900 volts with a good o2 sensor. a bad sensor will stay around .1 (or no volts at all).

You are just proving my argument for extraterrestrial acquisition of your mechanical skills.....

[FestYboy]

i'd better clam up then... can't let all the knoledge out, it would be too much for the whole of humanity.