[Mercury]

Hello!

A few months ago my jeep's check engine light was coming on and the codes ran for both O2 sensor being bad. I replace them both with the commended sensors on various Jeep forums.

Recently I've noticed my Jeep making a sputtering sound while driving. It also idles a little rough and has on a few occasions tried to stall when idling when the vehicle was at operating temperature. I've also noticed a slight decrease in performance. I scanned it and it showed the sensor two being faulty. I checked it today and now I'm getting three codes covering both sensors.

It seems strange to me that both of the sensors are suddenly showing as bad.

What could be causing this? Is there another proble
m with the exhaust? Is something upstream of those sensors causing a problem?

 

[doug schlosser]

what brand of sensors did you use

 

[Mercury]

what brand of sensors did you use

NGK or NTK, whichever one was recommended in the forum.

 

[Jerry Bransford]

NGK or NTK, whichever one was recommended in the forum.

That was the right choice, NTK makes both the NGK and Mopar O2 sensors .

 

[Jeepster20054liter]

So runs fine when cold when O2 sensors are not in the loop, then goes south once up to operating temperature and sensors were replaced. Plus engine starting to run ratty. PCM?

 

[Jeepster20054liter]

Also consider MAP sensor. Did you look at your fuel trims on your scanner? I believe high voltage at the sensors means your engine is running rich.

 

[Mercury]

That was the right choice, NTK makes both the NGK and Mopar O2 sensors .

I made that mistake a long time ago with a Bosch, never again.

So runs fine when cold when O2 sensors are not in the loop, then goes south once up to operating temperature and sensors were replaced. Plus engine starting to run ratty. PCM?

Doesn't run fine cold, still a little rough, but the stalling happened a few times warm and I think one time got close when it was cold.

I hope it's not the PCM.

Also consider MAP sensor. Did you look at your fuel trims on your scanner? I believe high voltage at the sensors means your engine is running rich.

I know my scanner shows it but I don't know what values I should be looking for. What would be the right/values? Would that indicate the MAP?

 

[Jeepster20054liter]

Here is my thinking. First O2 sensors are testable at least the basics and there are a couple of good tutorials o YouTube showing how to do it. Since you replaced your sensors and the new ones immediately took a dump, I am thnking this is not a sensor issue. Too many too soon.

So then I am thinking what talks to the PCM about fuel delivery and running cold the O2 sensors aren't on board until they are warmed up and start producing voltage. So what else talks to the PCM about adjusting the injectors and that leaves the MAP I think. Again there are YouTube videos showing how to test a MAP sensor with just a multimeter, I think that is the most helpful as you can see the MAP sensor working. Voltage output from the sensor is 4.6 volts at sea level (page 14-32 FSM).

Of course the PCM is in the mix as it is adjust fuel based on these amd multiple variables.

 

[Mercury]

Here is my thinking. First O2 sensors are testable at least the basics and there are a couple of good tutorials o YouTube showing how to do it. Since you replaced your sensors and the new ones immediately took a dump, I am thnking this is not a sensor issue. Too many too soon.

So then I am thinking what talks to the PCM about fuel delivery and running cold the O2 sensors aren't on board until they are warmed up and start producing voltage. So what else talks to the PCM about adjusting the injectors and that leaves the MAP I think. Again there are YouTube videos showing how to test a MAP sensor with just a multimeter, I think that is the most helpful as you can see the MAP sensor working. Voltage output from the sensor is 4.6 volts at sea level (page 14-32 FSM).

Of course the PCM is in the mix as it is adjust fuel based on these amd multiple variables.

Doing some digging on testing a MAP sensor. I'll use the DMM and then run the scanner at both cold and hot for the fuel trim. From what I've read it looks like vacuum hoses can cause issues with the MAP so I'm going to check those as well.

 

[Jeepster20054liter]

I take my time on this one. It just seems strange to me you have two sensors fail at the same time and then it happens all over again. You might just start by pulling a sensor and testing it yourself as shown in several videos online to see if the code you are getting matches what you see with your meter. Just a thought.

 

[Mercury]

I take my time on this one. It just seems strange to me you have two sensors fail at the same time and then it happens all over again. You might just start by pulling a sensor and testing it yourself as shown in several videos online to see if the code you are getting matches what you see with your meter. Just a thought.

Agreed. If one failed I would chock it up to a QC issue and just replace it but having both fail within two months of the previous pair just seems too strange. More likely it's something else going on.

 

[Digger84]

Sine 2 banks we know it is a 4.0 how about sharing year of TJ
Hopefully not 05-06 with the crappy failure prone NGC PCM

 

[Digger84]

I see signature says 1999
So is it Calif or Federal emissions
Fortunately 1999 has JTEC+ PCM

 

[doug schlosser]

you could have a bad catalectic converter

 

[Digger84]

Not following how a bad cat could effect the voltage to the heater circuit in the oxygen sensors
A bad sensor ground/engine ground sure could

 

[Jeepster20054liter]

Digger,

To test the ground hyporthesis couldn't he just aligator the body of the sensor to a ground some place accessible? I know some sensors use the body of the sensor as a ground (I know not this one).

Steve

 

[Mercury]

I see signature says 1999
So is it Calif or Federal emissions
Fortunately 1999 has JTEC+ PCM

Yes, it's a '99! Glad that year avoided some of those issues.

Regular with the one cat and two O2 sensors.

you could have a bad catalectic converter

My Jeep "might" be straight piped with a spoofer on O2 sensor 2.

Not following how a bad cat could effect the voltage to the heater circuit in the oxygen sensors
A bad sensor ground/engine ground sure could

Interesting. I'm planning to redo the engine ground with heavier gauge cable this weekend so if it it's just that it could be a good day for me.

 

[Jeepster20054liter]

Please follow up with anything you find. I would like to know how it ends.

 

[Mercury]

Please follow up with anything you find. I would like to know how it ends.

Definitely! I found a write up on how to test the MAP sensor. If that doesn't pan out I'll try testing the O2 sensors directly.

I'll have to wait until tomorrow at the earliest. Had a procedure on my wrist yesterday and didn't realize I'm not supposed to use my hand even with a computer mouse until tomorrow. I'm a temporary leftie.

 

[Digger84]

your issue based on codes appears to be the heater circuit for o2 sensors not the oxygen sensor function itself