Sensors rarely fail, just FYI, and replacing factory sensors is a roll of the dice, "new" doesn't mean what it used to
"New" once meant "tested and working"
"New" now means "you test it and we will replace it if it doesn't work"
So installing a new sensor, unless it is OEM Ford sensor and costs an arm and a leg, doesn't eliminate that sensor as the problem.
One of the reasons Ford, or any dealer parts, are so expensive is because most are tested before being shipped to Ford, one of the requirements.
O2 sensors do wear out since they use a chemical reaction to detect Oxygen levels in the exhaust, so these should be replaced every 100-150k miles, it will improve MPG, because as they get older they make the computer run engine Richer
MAF sensor needs to be cleaned every few years, MAF sensor causes the most bogging problems with the 4.0l OHV engines
It gets dirty even with good air filter
Cleaning MAF here:
http://www.therangerstation.com/tech_library/CleanMAF.shtml
Fuel filter changed every 5 years or so
There is an IAT(intake air temp) sensor that should be checked because of the "seems to run worse in hot weather" statement
It is on the upper intake, drivers side in the middle, 2 wire connector
Gasoline engines run at 14.7:1 air:fuel ratio, this is a WEIGHT ratio, 14.7 POUNDS of air is mixed with 1 POUND of gasoline to get the correct mix
Or 14.7 grams of air to 1 gram of gasoline
Cold air is heavier than warm air, i.e. "warm air rises", that's because it is lighter than cooler air
So...........the computer that adds gasoline to the engine needs to know the weight of the air coming in so it can add the correct amount of fuel.
MAF sensor compensates a bit for the air temp, but IAT sensor is still needed to get best mix
Unscrew IAT sensor and clean its end
It can be tested with OHM meter
Chart here:
http://www.aa1car.com/library/air_temp_sensor.gif
1992 Ranger will run 30psi fuel pressure from gas tank to fuel rail on the engine, so vapor lock is not likely, when engines used mechanical fuel pumps on the engine the fuel pressure in the line from the gas tank was 0psi so gasoline in that line could vaporize if fuel line got hot enough.
As pressure goes up vapor point of gasoline goes up, so while possible, it isn't likely at 30psi.
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