Engine Performance problem
1997 Dodge Dakota V8 Four Wheel Drive Automatic 166000 miles
I recently have been getting horrible fuel mileage with my dakota. I have knew wires, plugs, cap and rotor from a year ago. I just changed my oil recently etc. It sounds like it runs fine and I notice not hesitation or lack of power. About a month ago I had my thermostat jump to 240 so I pulled over, (where we live is cold so possibly froze a little in my block) got a ride to the store for anitifreeze and came back and temp went down. Im not sure if this info in relevant but I thought maybe it could help with my situation. I had it in the shop last week and had a fuel pressure test done and it all checked out. So I'm lost as to where and what to do to this thing to better my fuel mileage. I am getting 8 in town and no better on the highway.
The least costly way to find the problem is to take it to a professional with the proper diagnostic equipment. He will use a scanner to look for diagnostic fault codes, watch sensor readings, and read the long and short term fuel trims.
An exhaust leak before the oxygen sensor will trick the sensor into reporting a too lean condition. The engine computer will continually try to add fuel to reach the proper mixture. You should see black exhaust smoke and smell the unburned fuel. A failing MAP sensor can make the computer think the engine is under heavy acceleration and it will deliver too much fuel. The same thing will happen if the vacuum hose to the MAP sensor is cracked.
A misfire will result in unburned oxygen, (and fuel), in the exhaust system. The O2 sensor only detects oxygen, not fuel. As a result, the computer will add fuel to all cylinders, and it will still see a lean condition due to the unburned oxygen.
Worn bushings in the distributor will cause erratic timing, a surging engine, low power, and poor fuel mileage.
These are just a few possibilities. The least effective way to troubleshoot this problem is to blindly throw parts at in hopes one will solve the problem.