oxy.sensor 88

I Have A 1988 Voyager That Has Apx.170,000 On A 3.0 And The Gas Mileage Is Not Good It Probably Averages 17-21 Mpg Town & Hwy.mostly Hwy.isaw Where Oxy. Sensors Should Be Replaced At Around [100,000?]it Had Around 165,000 When I Got It.
I Guess My Question Is Do'es An 88 Have One If So Wher Would It Be Located At?

Dave you are going about diagnosing the problem the wrong way (hit or miss replacement of parts). Firstly, your gas mileage indicates a problem. It should be 22-23 mpg range.
When the computer detects a problem in one of its sensors, it sets a fault code and usually lights the check engine light. It can also puts itself into "limp" mode if the problem is bad enough where it will make guesses based on the other working sensors for the bad sensor it can't read. This is good in that it will keep the engine running, but bad in that it usually results in too much gas usage and poor engine performance.

First obtain the fault codes in the computer. Turn the ignition switch on-off-on-off-on-off-on (three times without starting car) and count the flashes of the check engine light. Each code is a two digit code, each flashing digit is seperated by a pause. The end of the list of codes is 55.

If you have another problem that results in too much gas going in, then expect the code for the oxygen sensor too to be set as a side effect of the real problem.
Next, to get the meaning of the codes, do a web search for sites with them listed, using the keywords - "Chrysler computer codes". This is a good starting point.

If you have 170,000 on the original motor, your getting pretty good milage. Oil comsumption thru worn valve seals and oil control rings are your problem. Spark plugs soot up quickly and beguin to misfire. The O2 sensor reads a rich mixture from the unburned fuel and reduces fuel supplied, causing a loss of power. You compensate for this by using a lead foot. Hence the loss in MPG.

saw your reply,sounds reasonable. i did however remove the plugs prior yo your reply and they looked good,i was checking to see i could see which headgasket was blown.
thanks for reply.