20 Oct 05 14:18
I have a 1996 Ford Aspire. A broken spark plug caused the spark plug wire to fall off and produced misfiring. It upset all my settings and possibly contaminated my oxygen sensors. I have replaced the unheated oxygen sensor with no correction to the 20% loss in gas mileage that has occurred.
I do not claim to have a full understanding of all of the terms but will use them as I know them.
For background, I provide the following. I have bought a 4-wire universal heated oxygen sensor(down stream). The purchased sensor has 4 wires which are white(heater), white(heater), blue(signal), black(ground). The information in Chilton's manual shows that the corresponding Aspire's wiring does not agree with the locations indicated as appropriate for new sensor's description of the Ford/Mazda connector wiring for the vehicle. In addition the Chilton's manual says that one should backprobe the sig rtn which would correspond to the ground wire to measure the output voltage. This is a common connection to other sensors according to the wiring diagram and I believe it is a common signal ground.
In addition, the colors of the wires do not agree with the Chilton's wiring diagram. At the wiring harness they are correspondingly physically B/W, B, O/B?, Y/G. The electrical diagram shows O/W(htr pos), B(htr grd), B/W(vpwr), Y/G(sig rtn). Y/G is clearly the common ground on a number of sensors on the diagram and I assume from this that it is correctly sig rtn as I believe that sig rtn is the same as "sig -".
To simplify the above I can state that I have verified that the first two wires are the heater wires. There is a 6.8 ohm resistance on the oxygen sensor which is about right. This leaves only the other two in question. If backprobing only the sig rtn gives the 0-1 voltage range, then I believe that the signal wire is the fourth wire. However, I am suspicious that it should have read to backprobe between wire 3(sig +) and wire 4(sig -, sig rtn). This would make the wiring agree with the information provided with the new oxygen sensor. It also would indicate that the fourth wire is not vpwr.
I have already wired the sensor with sig rtn connected to signal and the other wire connected to vpwr. I now suspect that this isn't correct but I am not sure.
Should I connect the wire 3(O/B? -> Blue) and wire 4(Y/G -> ground)? The electrical diagram shows O/B should be O/W and if so comes directly from the PCM and the Y/G is a common return for sensors(throttle position, EGR, etc) as well as the oxygen sensor. Notice the electrical diagram seems to be wrong about the heater circuit wires.
I do plan to check the voltage as a precaution to make sure that vpwr doesn't actually have any voltage applied.