I recently replaced the O2 sensors (ipdusa) on my car, and since then MPG reading on the computer has dropped from 19 to 14. I cannot figure out the reason(s) for this drastic change. cold weather could be one reason, still 4/5 MPG reduction is a lil extreme I would think.

The vehicle has 125K miles. Could Mass Airflow Sensor be the problem? It has not been replaced since 1996. Though a code related to MFS has never been set.

Also, is there a maintenance schedule to replace the Camshaft Position Sensor?

volvo 850 Turbo, 1996 model.

R

 

Did you disconnect the battery or anything when installing?

 

Battery was not disconnected. The O2 sensors are easy to replace - screw them on to the exhaust and plug it on ro the connectors. I did not get the Check light On after installing.

R

 

I know they're easy to replace, if you disconnected the battery the computer would have reset. Were your other ones completely shot, that maybe the computer is relearning the new ones?

 

The old ones were not dead, but were performing poorly. A mechanic at a dealership was able to check the performance of the O2 sensors.


I have unhooked the battery connection atleast once since then. I am not aware of the learning phase you mentioned in the last email. I had heard about new transmissions going through that phase, but not O2 sensors.

R

 

Well if you disconnected your battery than that's why. All the information you gather driving, for example: average MPG, is reset when disconnect your battery.

 

YES....If you replace any O2 sensor on these machines, You are required to reset the computer and disconnecting the battery fro about 10 minutes is the easiest way to do it. After that reconnect the battery and let the engine idle for about 6-10 minutes with no load (turn off all lights, blower,A/C etc). This will let thte computer learn the new idle based on feedback from sensors. Now, when you drive the car, it takes about 200 kms depending on few driving condition parameters and you should be able to get better figures on you info pannel afer this as compared to how they were before.

If you dont this reset thingy after replacing the sensors, the computer gives aweful figures because of deviations from the already plotted curve in its mind.

Hope this helps..
Good luck

 

Thanks for the info. I shall give it a try.

R