Those four fault codes just will not go away. I've replaced all O2 sensors, replaced the EGR Pressure Sensor. cleaned the MAF (which wasn't that old anyway, and wasn't dirty at all), and replaced the old spark plugs. I've also read that sometimes the OEM alternator causes voltage irregularities which could cause the injectors to fire too much fuel, so I replaced that as well. After 150 miles the fault codes still keep coming back every 20 miles or so. I pulled the plugs and they are running perfectly - no white residue (if it ran lean) and no black buildup (if it ran rich).

Here's a picture of the spark plug from cylinder 4 after 150 miles,



As you can see it's running just fine. There's no signs of the motor running rich at all - no lack of power, no smoke from the exhaust, etc.

What else could it be? Bad MAF? Bad PCM? After $135 for the alternator, $60 for each O2 sensor, $62 for the EGR pressure sensor, funds to keep throwing parts at it are getting dry.

Gas mileage is pretty average, getting about 12-13mpg around the neighborhood and around town.

Just trying to get this bloody CEL to go away.

 

well one 12 to 13 is shitty, even for a ranger. also what year and motor. i take it its 96+ due to the fact you have codes so i take its a 3.0? do you have a cold air intake, this has been known to throw weird codes, mine does this too if i drive at 2300+ rpms on the highway for 20min or more at one time. comment back, list your year, and all the mods you have done to your rig. could be something like that causing it. i got the k&n high flow off the throttle body with an aftermarket maf sensor, and a throttle body spacer. mine throws stuff like this because of it.