I am looking for a way to test O2 sensors to figure out which ones are bad out of the four that I have. Any info would be greatly appreciated. Ford says I'm not showing any codes but that doesn't explain why, in the summer time, I went from 14-15 mpg in the city to 11-12. And now that winter has set in I've gone from 11-12 down to 8-9. I figure it's probably the O2 sensors or the thermostat. My temp. guage read about halfway up in the normal area but for good measure I think I'll replace it. Please help if you can.

------------------
Red '97 F-150 SC 4x4 off-road, 16" rims instead of factory 17"'s(borrowed from old '97 reg cab), BFG 265/75 16 all terrain T/A, K&N filter with modified air box, Flowmaster 40 with duals out back, Expedition center console, 3" rear seat lift, after market stereo seen at HTTP://members.sounddomain.com/red97
Got Superchip and velocity tube for X-mas too cold to put on as of yet.

 

I too am on the same quest. My fuel economy has become dismal now that winter is here.

I recently purchased an AutoXray OBD-II scanner for my truck. It will allow you to monitor the O2 sensor signal voltages. There is an extensive O2 sensor diagnostic section, but it currently does not support our trucks. AutoXray said that they will have a Ford enhanced version available sometime this quarter.

I recently reported to the list that my truck was surging and hesitating at 1400 RPM. About the same time, my MIL came on. I used the scanner to read a "P0402 EGR flow excessive" out. I replaced my EGR valve and solenoid which fixed that problem, but I am still experiencing poor fuel economy.

When I view the O2 sensor signal voltages with my scanner, the left and right downstream sensors report different voltages. The voltage directly correlates to how rich/lean the mixture is. Since one is slightly lower than the other, I would have to imagine that the PCM is getting confused and is fighting with the two different readings.

Sadly, I do not have a baseline, so I do not know which voltage is the correct voltage. I am thinking of blowing the $240 necessary to replace all four sensors. I still haven't made up my mind yet.

If you find a way to accurately test your O2 sensors, please let me know!!

 

I spoke to my mechanic friend last night and he said that there wasn't a way to test O2 sensors. So I may have to do the same and blow the money to replace them. Thanks for the reply.

 

Can anyone tell me exactly how many O2 sensors there are and exactly where they are.

I have been told both two and four, and
have only found one.

 

There are 4 O2 sensors on the 4.6. Chiltons says the output when warmed up should be between 0.01 to 1.0 volts with a digital meter & fluctuate quickly. So far the 2 I had bad lit the check engine lite.

------------------
97 Lariet-sc-4.6-4x off road-auto-3.55 LS-
superchip-K&N-3"
pvc air box mod-Granetelli MAF

 

Believe it or not I have been driving the last 30,000 miles with the check engine light on.No codes ever come up on the computer but they were also leaning to the possibility of bad O2 sensor.I want to know if anyone has replaced them and it took care of the problem.I to do not want to spend the money on a lost cause.