Bosch 02 sensors = Bad MPG?

Do you have any MPG problems to report?

12-14mpg on average isn't fun when I used to get 16-18mpg on average. I can only get 16-17mpg MAX when driving 65mph long distances, and I used to get 20-21mpg.

I've got everything else I can think of checked or fixed. This Bosch 02 sensor is the last thing to look at. I'm tempted to go to NAPA and spend the $50 on an NTK sensor.

The Bosch was replaced maybe 20,000 miles ago, and I was seeing around 15mpg-17mpg afterwards, but I thought the Jeep had other problems that needed to be fixed that were causing bad MPG. Over the course of the last three years the MPG has gone down even more while nothing else seems to be wrong with the Jeep.

Any input is appreciated.

Obvious stuff has been done such as tune up, air filter, TB cleaned, no exhaust leaks, ect.

Have you tested the sensor, and tested it live?

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=oxygen+test

I have not tested them, and do not have a multimeter to do so. I am not familiar with diagnosing electrical problems at all either. I will check the wires for now.

BTW, I forgot to mention that this is a 2000 Cherokee with 117,000 miles on it.

Also, there is seemingly excess amounts of exhaust coming out of the tail pipe. It spews clouds of exhaust in the winter, more than any other vehicle I have seen.

The exhaust has no distinctive smell either.

Curiously enough I have the same symptoms as well with a Bosch sensor. Mileage just seems to be taking a hit and I changed it like over a year ago and there's an excessive amount of condensation coming from the tailpipe. I suspect a vac leak cause its idling on the high side and/or might need a timing chain replacement as I hear a rattling on the front end. Will keep a lookout on this thread.

Time to learn. Google some youtube videos, it is childs play! Multimeters are cheap, compared to GAS!!

LOL

Bosch oxygen sensors seem to work fine on RENIX (87-90), but I recommend NTK on the 91-01.

That being said, it might not be the cause of your gas mileage drop. Winter weather, winter blend fuel, idle time, etc. are in play. Not unusual to see a drop in mileage in the winter months in the cooler climates.

I see a 1 mpg drop in winter even here in Houston. Mine are renix. I use the Bosch, but Bosch invented the O2 sensor and was I am told the OEM sensor for renix.

birchlakeXJ said:

Bosch oxygen sensors seem to work fine on RENIX (87-90), but I recommend NTK on the 91-01.

That being said, it might not be the cause of your gas mileage drop. Winter weather, winter blend fuel, idle time, etc. are in play. Not unusual to see a drop in mileage in the winter months in the cooler climates.

Click to expand...

I agree, also could be an O2 heater issue in the wires, relay.

Did you check for error codes? And lose connections or abraded wires?

birchlakeXJ said:

Bosch oxygen sensors seem to work fine on RENIX (87-90), but I recommend NTK on the 91-01.

That being said, it might not be the cause of your gas mileage drop. Winter weather, winter blend fuel, idle time, etc. are in play. Not unusual to see a drop in mileage in the winter months in the cooler climates.

Click to expand...

I have been logging MPG for a few years now, and am quite familiar with the usual drop in winter gas mileage. Usually 2-4mpg is lost depending on 4wd use. The winter gas alone causes me to loose 2mpg right off the bat. So I am actually getting around 10-11mpg right now with light 4wd use, and warm-up times less than a minute. Summer time I see 14mpg on a good week.

No codes, and I checked the 02 sensor wires today. All is good with those. I'll see about checking them with a multimeter.

Do you guys think $120 in labor is a fair deal to have someone change the front axle U-joints for me? I'm buying the U-joints at NAPA.

Not sure of your budget, but if you remove the O2, you might as well just replace it for $40. Don't waste your time testing it, if it's old.

Kill 3 birds with 1 stone, depending on your budget ...If you do the u-joints, might as well replace the hub bearings at the same time. I think Timken for $75/ea. Raybestos for $57. Pads/rotors also would be free labor. All need to come out anyway.

bimmerjeeper said:

Not sure of your budget, but if you remove the O2, you might as well just replace it for $40. Don't waste your time testing it, if it's old.

Kill 3 birds with 1 stone, depending on your budget ...If you do the u-joints, might as well replace the hub bearings at the same time. I think Timken for $75/ea. Raybestos for $57. Pads/rotors also would be free labor. All need to come out anyway.

Click to expand...

02 sensor isn't that old, only has around 20k on it.

My budget isn't going to allow me to replace things that aren't broken yet. Hubs are tight and spin just fine. Pads and rotors a new as of late last summer.

Where can I get Timkens for $75 though?

RockAuto.com

Ecomike said:

I agree, also could be an O2 heater issue in the wires, relay.

Click to expand...

Found out the hard way that Heaters on OBDII Cause an error code (O2 Sensor Heater failure) and a stumble off idle when the truck goes closed loop but the O2 Sensor is not up to temp.

Sounds like the O2 Sensors are working. The $10 question isn't whether they are working, it's whether their calibration is off.

Not sure if you can test that with a VOM and a vehicle which indicates it's running right (No Codes or Driveability issues).

x2 on Rockauto.. like $30 or so for an NTK.

WB9YZU said:

Found out the hard way that Heaters on OBDII Cause an error code (O2 Sensor Heater failure) and a stumble off idle when the truck goes closed loop but the O2 Sensor is not up to temp.

Sounds like the O2 Sensors are working. The $10 question isn't whether they are working, it's whether their calibration is off.

Not sure if you can test that with a VOM and a vehicle which indicates it's running right (No Codes or Driveability issues).

Click to expand...

Because all my rigs are Renix (except the 85 diesel), and they all have had so many bad ground and wire problems, it is not unusual for readings at the sensor to be different from the readings at the computer. So I have learned that what you see (at the sensor), may not be what you get, at the ECU or PCM, LOL. The PCM can be fooled and fail to give a code.

I suspect many HO OBD-I and II rigs are getting old enough, they may start having similar issues. Also the O2 sensor wires are know to get chewed up by road hazards, drive shafts, steering shafts and exhaust manifolds that may go unnoticed or not get fixed properly, or they cause other wiring issues if they were previously shorted in prior road hazard events, and the neighbor wires were damaged just enough to cause some signal degradation!!!

Moral of the story, no OBD-II code does not mean as much as most people think.

I chased my tale on a 96 ford forever last year that never gave me a miss fire code, but the idle was rough, and one hard to reach or see spark plug wire had come loose. It ran smooth as glass at 1500 rpm or higher. It never set a CIL, but it also never set the last emissions monitor, which was not obvious unless you were checking them with a scanner. What I did not realize was that the last emissions monitor had to be set and locked before it was smart enough to issue a miss fire CEL light and code!!!!

That is a serious software error!!!

I have also seen OBD-II rigs where the heater voltage to the O2 sensor heater was there, but was only something like 4 volts due a bad relay, wire or shorted heater in the sensor itself that never set of an OBD-II code or CEL.

Well, my NTK o2 sensor got here from Rockauto. $2.98 for shipping from California and it shipped Monday! Thats fast and cheap. Came well packaged in a box.

Anyways got it in and reset my ECM using this method.

Disconnect positive battery cable, touch to a ground for 30 seconds (fender, AC compressor, ect)

Reconnect battery cable, then turn key to ON position.

Turn lights ON, then OFF.

Turn key to off position.

When I started it up, I noticed that there was much less smoke coming out of the exhaust. When it's cold the jeep always pours out white smoke from the exhaust that has no scent. It doesn't burn oil or coolant.

With the new 02 sensor, there was maybe 1/3 the smoke coming out.

I'll let you guys know. I knew I should've bught a multimeter to test the old 02, but meh.

So any results on this?

Id be curious as well if there was an update to report.

My daughters 97, which I picked up for her 16th this last May, has been getting 11 mpg (average) and though Ive installed new plugs, cap, wires, etc I have always suspected the O2 sensors. I just installed 2 new NTKs and found out that the previous owner had installed a bosch in the upstream location (d/s was still stock). I plan to give it a week but ill report back any changes. hopefully the other guy will too:rtm: