Cadillac Repair: 1990 Cadillac DeVille, fuel pressure regulator, cadillac deville

Question
If the spark plugs have been changed plus the oxygen sensor that leads to the exhaust and the car doesn't have a miss, what could be the reason for the vehicle to burn gas more than normal? 1990 Cadillac DeVille 4.5 engine  

Answer
Hi Chris, Provided the sparkplug wires, cap and rotor are ok and the injectors are spraying correctly then the fuel pressure regulator could have a small hole in the diaphram allowing fuel to get sucked into the engine through the vacuum hose. The map or baro sensor could be miscalibrated. And the tps has a voltage range between .45-.55 volts at idle. The closer to .45v it is the less gas it should use. There is a procedure for setting the timing, min. idle speed, max. isc motor extension and then relearning the computor that has to be done and that will also influence mileage. For example if the relearn or one of the adjustments was done wrong you might not need the accellerator pedal to attain or maintain 30mph. Hope that helps. Bill