I have a 99 cherokee classic on 31s with a 3 inch lift normally I can get like over 200 miles out of a tank this week 65 miles and I'm a a half check engines coming on and off I had it scanned its saying the o2 sensor by the exhaust could that be doing it?

 

hmmmm. so the gas mileage drop started at almost exactly the same time that a key engine component started acting up and throwing codes.

couldn't be that..

 

Not like an o2 sensor is important for fuel economy or anything...

 

No it's been throwing that code on and off for a while with no gas milage change and the lights off right now and it's been off of the past 3 days and that's when I filled up

 

And it was the muffler one not the manifold one its running normal also always thought the one by the muffler didn't have a huge impact

 

Should still replace it. It could be faulty and sending inaccurate data to the computer.

 

Ok might as well try if that doesn't help any other ideas ?

 

how many miles?

has it had the injectors cleaned or fuel filter replaced?

if miles are above 100k and those are both no i'd do that too even if the o2 sensor does help.

 

The o2 sensor after the cat has no bearing on how the truck runs. It just tells you if the cat isn't working correctly.

Scan the codes and post up what code is thrown. It could be the upstream sensor.


My wife's TJ has its downstream o2 sensor zip tied to a heat shield right now. Plugged in, but reading nothing.

Runs fine, perfect mileage for a Jeep 4.0

 

It has 150k never did a fuel filter and I've run injector cleaner threw it a few times ill have it scanned when the light comes on again

 

I'll have to disagree with Gee oh Dee. Here's some text from Dodgeram. org that talks about the downstream O2S affecting fuel economy.

Upstream Oxygen Sensor Goal Voltage
From Star Center News #5, February 2000 - tests for those who have access to OBD II or OBD III code readers.

Since the introduction of OBDII with both upstream and downstream O2 sensors, the downstream O2 sensor has been used to evaluate catalytic converter operation and to control converter efficiency.

When looking at the upstream goal voltage, it should fluctuate above and below the normal center (.4 to .6 volts) based upon what the downstream O2 sensor is reading. The vehicle should be driven through all speed ranges when checking goal voltage. If the goal stays high or low all the time, a thorough check of the downstream oxygen sensor should be made. Be sure you check the sensor, wiring harness, connectors, catalytic converter, and inspect for exhaust leaks.

Although a MIL lamp may not be illuminated, there are instances when the downstream O2 sensor goal voltage is out of range, causing driveability problems or low fuel economy.

If the downstream O2 sensor tends to stay below center all the time, the PCM will adjust the goal voltage higher in an efforet to correct the low O2 readings of the downstream sensor. This can result in low fuel mileage.

If the downstream O2 sensor has a tendancy to stay above center, the PCM will set a low goal voltage which results in a lean fuel mix which can cause the engine to run hotter and aggravate a spark knock condition.

Sometimes a service technician will reset the PCM and take it for a test drive. The PCM does a recalibration after the reset, and the problem may go away until the PCM has completed a relearn of the system and then begins to attempt to correct for the downstream sensor error. If the symptoms reappear after several days of driving after a service is performed, check the downstream O2 sensor, the exhaust system, the wiring, and the catalytic converter. Note: a worn out catalytic converter can produce symptoms similar to a bad downstream O2 sensor.

 

Ok because I started it up today(cold start) and it smelled rich and there was a lil smoke it's the factory catalytic converter it could be shot but idk ill change the sensor and see if it helps

 

Yeah if it's running rich it's most likely the O2 sensor(s)

 

This would be a great reason to ask your boss for a raise.

 

Like Gee oh Dee, our downstream is zip tied......mid teens farting around town, 20 hwy.