metro mpg

Greetings

I have a 98 metro that I bought new and have always been a bit disappointed with the gas mileage (36-39). Window sticker claimed 50. I just found the forum and have been reading some of the messages. Could someone explain how the OBDII software and the sensors related to the mpg works and is there a way to retrofit the 98 to the pre 96 to achieve the better gas mileage.

Thanks
moody

Well, "retrofitting" would be a bit difficult. It would require a new ECU, wiring harness, intake manifold, and distributor. OBD II software is used to reduce the amount of NOx(noxious) gasses emitted from the exhaust. It sounds like a good idea, because NOx gasses are toxic. What the EPA has noticed lately, is that the new OBD II vehicles emit 4-6 times the amount of CO2 than the old vehicles. What it does is make the engine run a little more rich by adding more fuel per cycle. By doing this, some un-burnt fuel will continue to burn past the combustion chamber, causing the cat converter to heat up more. Also, the less oxygen rich gasses are converted much easier in the converter. So to make a long story short, more gas=less toxic+more greenhouse-gas mileage. The OBDII systems use a crank postition sensor(next to the oil pan under the timing belt) to synchronize timing more accurately than just the hall sensor in the distributor. A better (cheaper) way to gain gas mileage is to add a digital ignition ($260) and run your own fuel maps and ignition timing, by bypassing the ECU. 50mpg is a bit far fetched unless you're driving downhill most of the time. A 5 speed 3cyl metro should average 38-45mpg if driven VERY gently. A 4cyl should average about 34-40mpg. These numbers are also determined by how accurate your engine's sensors (hall, CPS, O2, ITemp, WTemp) are, what shape your EGR is in, how clean your intake and valve seats are, how plugged your CAT is, steering alignment, tire pressure, cap and rotor, plug wires, plugs... Make sure everything is good. Sorry for the book, but wanted to cover everything :smokin:

Thanks for the info. Sounds like you know what you are talking about. My metro has 121000 miles and still runs great (5 speed 3 cylinder).