i have a 99 ranger, just replaced muffler .I keep getting a 171 and 174 code replaced all o2 sensors and i keep getting the same codes. there getting voltage to them. it normally runs about 25 miles and sets the codes.but not always it stayed off for two days then came back on im stumped thanks for any info

 

Intake manafold vacuum leak or a dirty MAF can cause the 171/174 codes. I would start with cleaning the MAF sensor with CRC's new MAF cleaner. Just did this on a 2000 Windstar that I replaced the intake gaskets on back in June for the same issue. First 171/174 codes was caused by bad intake "O" rings, and the last ones was caused by a dirty MAF sensor.

 

thanks for the response as soon as i get a day off ill try it