1993 Mazda Protege Drastically reduced fuel mileage

MEGHANO1989

MEMBER
1993 MAZDA PROTEGE
4 CYL
2WD
AUTOMATIC
75,000 MILES

I got this car a little over a year ago. For the first 10 months or so I was getting 27-28 MPG. I check my mileage every time I fill up. For the past few months my mileage has decreased to around 20 MPG. There are no puddles under the car & no smell of gas. I frequently check the tire pressure and change the oil as per the manufacturer's suggestions. The spark plugs were replaced right after I got the vehicle. The exhaust system and all belts have recently been replaced. I have been able to find no reason for this drastic reduction in mileage and I am sick of go to the pump so often! Any ideas as to what might be causing my problem?

1 Reply

F4I_GUY

MECHANIC
3,302 POSTS

Hi meghano1989,

Unfortunately your vehicle's computer system is OBDI, unlike 96+ models which are OBDII. OBDI system's do not monitor the 'lifespan' of sensors, so if you have an oxygen sensor that is acting a little lazy or out of spec, the check engine light will usually not be illuminated.

What this all means, is you may want to check for any codes first, to see if there is a sensor acting up, if not you may want to hook up a scanner to it and read the PID'S (the data for each sensor). I'd look at fuel trims to start and then possibly scope out your oxygen sensor. This all requires speciality equipment.

If you want to check it out at home, you can remove each spark plug and compare them to each other. If one plug is more white or darker than the other this may indicate a problem with this particular cylinder. Some other things to look at would be fuel pressure, vacuum leaks, tune-up items (air filter, fuel filter, spark plugs, wires, cap, rotor, etc)