Help O2 Sensor Diagnostics

[joefnh]

I have a 4.0L 4x4 2003 Explorer with 92000 miles. I have noticed a recent drop in gas mileage for which the bank 2 front O2 sensor appeared to be bad (see images)

I decided to replace all 4 O2 sensors given the mileage, unfortunately this did not fix the problem of low MPG.

If you look at the images of the 4 O2 sensors bank 2 front appears to not be switching correctly even after changing it out. I assumed that the heater wiring might be bad, but after testing the + 12Vdc heater voltage was present. I changed out the sensor again, no change

To address other issues related to loss of MPG I replaced air filter (KKM FIPK - lightly oiled), cleaned the MAF, IAC, replaced plugs and wires. I also checked the fuel pressure and vacuum, all readings were normal (according to chiltons)

On the bank 2 side (drivers) I also looked at the plugs for signs that the mixture was indeed running too rich. The plugs were light gray in color with no carbon buildup.

HELP

Thanks in advance

--Joe

Below are the images from the SCT data logging software of a 55 minute drive combined city and highway speeds

 

[aldive]

Are you using an aftermarket "tune" with the XCal 2?

 

[joefnh]

Al I have been using the same tune from Doug for 89 octane MPG since last July

I also tries restoring to stock to see if that might help, no change.

--Joe

 

[aldive]

Al I have been using the same tune from Doug for 89 octane MPG since last July

I also tries restoring to stock to see if that might help, no change.

--Joe

Joe, Doug's tunes turn off the rear O2 sensors.

 

[Glacier991]

That front sensor graph on bank 2 is seriously disturbed. before impugning the sensor we should explore possibilities of why. What are your fuel trims for that bank?

 

[Glacier991]

BTW this kind of info in a help request is GOLD ! Thank you.

 

[joefnh]

Galcier & Al thanks for the response. Al this tune has the rear O2 sensors enabled.

Glacier here are the images from a 68 minute trip mixed city / highway driving, the highway driving was mostly in the middle of the trip.

Listed are the bank 2 fuel trim and the data from both the bank 2 front and rear O2 sensors. I should note that the front sensor has been replaced twice and I have verified that the heater voltage is present.

It should be noted that the 3 spark plugs on the bank 2 side of the engine look similar and are a light grey in color with no carbon buildup

Thnaks again for the help

--Joe

Glacier here are the fuel trim images.

 

[aldive]

Galcier & Al thanks for the response. Al this tune has the rear O2 sensors enabled.

Any reason the rears are enabled?

 

[joefnh]

Not sure, thats the way Doug set them up.

What are the adavantages of disabling them?

I did note the section in the pro racer software where you could disable them.

--Joe

 

[joefnh]

Update...

I finally figured out the problem today. While troubleshooting , I had replaced the o2 sensor twice with Bosch sensors purchased at Auto Zone a local car parts store.

Apparantley the 03 Frod Explorer uses 2 types of sensors, a 3.3 ohm and a 6 ohm heater coil type. The 3.3 ohm ones are used in the front or upstream positions while the 6 ohm ones are used after the cats. Auto Zone apprantly did not know this.

In Fords service DVD manual the reason given for this is so that the front sensors can heat up faster (as the 3.3 ohm heater will draw roughly twice the current of the 6 ohm heater) to enable the engine to enter the closed loop mode sooner.

After swithching out the sensor with the correct model it ran fine.

Thanks again

--Joe