My gas mileage has gone from 30MPG down to 20MPG. Things I've done.

[sstupid]

Hi, guys. I'm new to the forum. I have a 1991 Honda Civic Hatchback Base with 183K. It's just a beater, but I love her for her gas mileage..............or I did anyway. My gas mileage has gone from 30MPG to 20MPG in the last 3 months, slowly. It crept to 28, then 24, then 21, and now 20.


1) New air filter.
2) New spark plugs, gapped correctly.
3) New spark plug wires.
4) New O2 sensor.
5) Tire pressures are all at 35 PSI.
6) Junkyard MAP sensor. When it didn't work, I put my original back on. Of course, I don't know if they are both bad. I don't know how to check them for correct operation.
7) New oil change with 5W-30.

Any ideas, anyone? Is there any way I can check that my O2 sensor is working correctly? Is there a way to check that the MAP is working correctly? I definitely have a strong gas odor when I drive with just my driver's window down. When I use my A/C in the summer, I'm used to seeing 22MPG, but this has been during the winter and I'm not using the A/C.

 

[RonJ]

I think you should get better than 30 mpg for a 91 Civic hatch. Is it stock with a D15b2 engine? What type of driving? All city?

1) You need to do a full ignition system tune up that also includes replacing the cap and rotor and adjusting the ignition timing.

2) Any CEL codes?

3) Is there an exhaust leak near the O2 sensor?

4) Is the engine running cold?