Tuning an 1993 Geo Metro Up from 32 MPG.
 

200K Miles 1993 Geo Metro 2 Door no frills Geo Metro.

Want to restore it to the 40 MPG Range.

Replaced all the ignition components and all the plugs are Grayish white so the actual ignition process is working.

$850 Car so the strong motor and transmission are all I could expect.

So what are the Top Ten Things to inspect to get an extra 8 MPG?

Change your driving habits to suit your commute. Also, remember to replace all fluids, grease all fittings, and inflate your tires to specified psi/max sidewall rating/mild over-inflation :thumbup:. Once you feel comfortable with your driving technique, you can move on to areo-modding (if you do long highway commutes) or tuning of the engine (in general, slightly expensive). Good luck and welcome to Ecomodder.

Automatic or manual?

Manual. This is the three door basic model.

Compression check out?

I'd have to wonder about O2 sensor with mileage in the 32's (unless you're driving it like a demon).

Yeah I was thinking O2 sensor too. $100 part I won't change it out without more evidence.

Tuning to distant AM radio and listening to the RFI from the engine there seems to be a misfire under some partial throttle circumstances. Idle OK, Full Power and Hi RPM OK.

33 to 66% of throttle...I have a bug to track down and kill.

93 should have a one wire O2 sensor. You can swap it to a 4 wire from a junkyard pretty easily with just a minor bit of wiring. That will give it a faster startup and keep it working even at idle when the one wire cools off and stops working. It is a slight improvement over the stock one wire and is worth considering when having to replace it.

4 Wire Oxygen Sensor conversion - MetroXFi.com

Just replacing the one wire sensor with a new one is normally pretty cheap. Last one I bought was like $15.

I would guess 45mpg is normal for an easy driven base 5spd. So first thing is do a compression test. It should be over 175 or so. If one cylinder is lower than the others then it probably needs exhaust valves. Just get the stainless ones from 3tech and they will never go bad again.

If compression is ok then next is O2 sensor. You can take it off and test it with a propane torch and voltmeter as listed in that link instead of just replacing it.

Next I would check the brakes/wheel bearings. The rear tires should spin forever about like a bicycle when you jack the back end up and spin them. If the brakes drag or the bearings are bad it won't spin real easy. The front should spin pretty easy but the disk brakes have a lot more drag than drums so it won't be quite as good. An easy way to check them is to jack both wheels up and let it idle in 1st gear and see if it favors spinning one wheel over the other. Get full loaded calipers if one of them is dragging. It is usually the slider pins that get stuck and are very hard to get working properly again without just replacing the whole thing.

Those are the main things I can think of that cause bad mileage. Hopefully you can get it back up to just under 50mpg with easy driving and keeping it 55mph and under.