[crappy tranny]

i noticed when i bought the van that the gas mileage was poor about 14 mpg so i replaced the o2 sensor and fixed the prob. got about 23-24 mpg not to long after that the head gasket blew when i replaced it i was back down to around 14 mpg so i figured the o2 was contaminated and replaced it again which fixed it. now for no reasin i can think of im back down to 14 mpg all three times got codes 21 51
is there anything else that might be causing this

 

[Dodgevanman]

What are those codes?

 

[kuksuldo]

Regarding 92 Caravan 3.3 L engine, I wonder what if O2 sensor is failing or getting bad, what is the results? How many O2 sensor are located in this car?

 

[crappy tranny]

i went ahead and put another o2 sensor in and the gas mileage is back up to around 23 mpg and for the first couple of days no codes i checked yesterday and good ol code 51 is back which usually meens 21 will be following and the gas mileage will drop again what the hell is causing this