So now my moms jeep is acting up. Its a 04 WJ with a 4.0 I6. Has around 160k on it. Its running rough. By that I mean is shakes kinda hard around 1500 give or take a few hundred. The codes that came off were O2 sensor which was there before and didn't bother it much. Another code that concerns me the first time we pulled the codes, one was cylinder 3 misfire, but after resetting it no longer showed up. We cleaned the map sensor and it seems have made smoother around the idle rpm but it still running rough. Any suggestions? Please help!!
Did you check the plugs and air filter?
Which O2 sensor code you have? A bad O2 sensor can make it run too lean and finally cause misfires if the mixture becomes too lean to burn.
Did you check the plugs and air filter?
Which O2 sensor code you have? A bad O2 sensor can make it run too lean and finally cause misfires if the mixture becomes too lean to burn.
Is that a Jeep thing? On other vehicles I've had if the front O2 sensor goes bad the computer is set to mixture rich to prevent a lean mixture that can lead to detonation.
If a tune-up was not done lately and dont know when the plugs where changed, its maybe a good idea to buy new ones. Use only the standard copper core plugs. You could just check them and clean/ gap them if not worn too far down. Also a clean air filter is a must. If that doent help, then you could run some seafoam through the brake booster line and some in the fuel tank. Eventual carbon buildup will be removed and the fuel nozzles cleaned.
here is the list of the codes we pulled. Among other bad things I have described before:
P0031 - Oxygen Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
P0051 - Oxygen Sensor Heater Control Circuit Low (Bank 2 Sensor 1)
P0303 - Cylinder 3 Misfire Detected
P0136 - Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
For the first two codes, have a look first at fuse 16 (15A) in the power distribution center under the hood. If its blown, you will have to check the wiring of the upstream O2 sensors for chaving or melted isolation due to touching hot exhaust part.
Did you check/change the plugs and did you see anything special on the #3 plug? If the code persists, you could swap the coil from #3 with #1 and see if the fault will follow.
For the last code i would check the wiring from the bank 1 after cat O2 sensor. If you have a scanner which shows live data, you could monitor the O2 sensor voltage and compare to the bank 2 reading.
UPDATE: so we have replaced all 4 o2 sensors and my dad replaced the relay. Now, here is the issue. When the ignition is just on, before you crank to get it started, the fuse for the o2 sensors blows, thus giving the codes. After looking at the schematic from the Haines manul it looks like it can only be something called o2 sensor upstream? What is that, where its located and how to replace it?
If its not that, then there is a short somewhere between the fuse and the sensor
O2 sensor upstream is just the before cat O2 sensor. If the fuse was not blowing before the O2 sensor change, I would start measuring the O2 sensor heater resistances.
I do remember that the fuse kept blowing before the sensor change. Thats what made us change the sensors in the first place. We thought one of them was short.
So now you will have to check the wiring from the PCM to the O2 sensor connector for shaving or melted isolation. If you don´t see anything wrong, you will need to measure the wires to ground and see if it indicates some short.
Ok, attached the wiring schematic for the O2 sensors. Your jeep most probably doesn´t have the hydraulic cooling fan, isn´t it? Because the hydraulic cooling fan module is also fed via the same fuse #16, but if you would have this cooling fan and the fuse blows, you also get a fault code for the hydraulic cooling fan solenoid, which you don´t have.
So my previous words of measuring between PCM and O2 sensor was wrong, because you should measure between the fuse #16 (pin 17) and ground. Most probably you will measure a short and will have to check the wiring between the PDC and the O2 sensor connectors. There must be a shaved or melted isolation of one of the O2 wires.
You could remove the downstream O2 sensor relay in the PDC for trouble shooting, if the short is gone with the relay removed, then most probably the short is in the wiring to the downstream sensors. If the short persists with the relay removed, then you will have to check the upstream sensor wiring.
Yeah sorry, i only looked at your signature and didn´t remember the first post saying it is regarding a 4.0L. For the O2 sensors power feed there is no real difference. Its just a straight power wire from the fuse #16 to the upstream sensors and via a relay to the downstream sensors. If you remove the relay for trouble shooting, you can determine if the problem is with the upstream sensor wiring, or the downstream sensor wiring.
UPDATE: So we eneded up replacing crankshaft position sensor as well as the 4 O2 sensors. Now the Jeep is fixed and running fine. Also figured out where a clickkin noise was coming from. Turns out, when we had the transmission rebuilt, the guys didn't secure the transfer cse shift cable correctly and it has been grinding in the front driveshaft the whole time. Now, part of the cable got "shaved off" and there is a shiny spot on the driveshaft where it used to grind. But for now he is working and no major problems.
The fuse doesn't blow anymore. All o2 sensors were replaced only once. And a friend of mine recommended to replace crank sensor after my dad stalled twice in one day on the stoplight. He said his merc did similar thing. So we did that and it works fine now. May be the timing was going bad. Still a mystery on the fuse though. My dad put in a 25 A fuse instead of 20. I trust him on that cause he is and electrical engineer so its all good for now. Will see how it all works out later
According the service manual fuse 16 is a 15A fuse. Replacing it with a 25A fuse could result in melted wire isolation or even burn the wire away. Do you know which brand of O2 sensor was installed?