2002 Jeep Grand Cherokee P0141 & P0161

My guess would be to change the o2 sensors with ones from the dealer. I just had a O1 Intrepid that the customer was working on before bringing to us. He changed all 4 o2 with ones from autozone(bosch) and later the light came on and was stalling and all kinds of problems. Long story short the downstream o2 sensors were not even correct the plugs are slightly different and bosch only listed one part number for this car. The PCM want's to see a certain voltage drop in a certain period of time on the heater circuit and if it does not see this it will trip the light with the listed codes.

Ascent is likely correct, the fact that the drivability has improved now, no stalling etc just a cel and a code can almost confirm that the 02's were causing the engine to overfuel and lead to the flooding etc, pretty common on the jeeps. They can also generate your cam and crank codes as well when they short. Unfortunately a Bosch 02 and a Bosch plug seem to make a dodge run worse. They seem to be okay replacements in a vehicle that used them from factory ie some GM's toyota's etc but the heater element in them doesn't run hot enough to satisfy the pcm requirements. If you wish to run an aftermarket part in your jeep I'd suggest an NTK brand 02. It's been my experience that when it comes to engine contriol parts the OE is normally the best source. You have to remember that the OE is the largest purcahser of parts before the vehicle rolls of the line so if there was something cheaper that worked good enough they would have used it!

Thanks guys. The other day I cleared the codes out to see what happens. On my way to work this morning the engine light came back on. I assumed it was these codes coming back. I saw the posts today and decided I would go to Jeep this weekend and get OEM O2 sensors and replace those. Once I got home I checked the code and it is showing P0301 (Cylinder #1 Misfire) in the odometer spot and the engine light flashed 12 times. I had gotten the other codes using a scan tool so I am not sure if that engine light flashing means anything. Any thoughts? Possibly bad wiring or she needs a new PCM? Or should I still go ahead and replace the O2 sensors with the OEM ones from Jeep and see what happens?

Do you mean the light flashed twelve times as you were driving it or you were using the cluster to display codes? if the cel flashes it's missing pretty good! Is your jeep a 4.0 ltr 6 or 4.7 8? If it's the 4.7 then check the plugs and try changing the coil to another cylinder to see if the misfre code moves, if it's a 4.0 ltr then I'd be suspectting carbon buildup on the valves! Either way I'd still replace those 02's with the oem parts.

The engine light only flashed after I checked for the code. I turned on/off, on/off and then on. The odometer read 'P0301' then read 'done' and then went back to the mileage. Then a second or so later the engine light flahsed 12 times. It never flashed while I was actually driving. I didn't know if that meant anything since back in the day the codes were determined by counting how many times the light flashed. It is a 4.7 V8. I am definitley going to change the O2 sensors to OEM this weekend and keep my fingers crossed that that does the trick. Thanks so much for all of the suggestions and help. It really is appreciated because this is such a frustrating process.

code 12 was for battery disconnectted within fifty starts but it would flash 1 blink then 2 blinks for the number 12. Im unsure about 12 blinks like that because I've never spent much time pulling codes that way! Do you feel a miss?

Replaced the downstream O2 sensors with Mopar parts as well as the cam sensor today. Going to take her for a ride later today. Seems to take 2-3 weeks to throw another code so I will keep you posted. Thanks for all of the helpful information. If it does throw another code, does anyone think that it might be a faulty PCM?

No!

Engine light came back on this morning and throwing the P0301 code again. Forgot to note in previous post that I also changed the spark plugs. Any thoughts?

Yeah switch the coil to another cylinder, check for a broken valve spring or slipped rocker on that cylinder, check cylinder leakage, switch the injector to another cylinder if you want!

Put a new OEM coil in cylinder #1 today. Tested the old one and it tested fine based on the Haynes manual. Checked the injector on #1 and compared to 2 other ones and resistance was fine. Checked resistance on TPS sensor and with throttle closed it was fine and on wide open throttle, it was 3.8 and the manual said it should be approximately 4.5. I guess this is close enough. I drive 26 miles each way to work on the highway everyday so I don't think that the cats are clogged. If the rockers arms are falling off, then wouldn't it be making noise? There is no antifreeze in the oil and there is no oil in the antifreeze so I don't think I have a cracked head gasket. It doesn't feel like the engine is skipping so I don't know what it is throwing the misfire code. She has always run a little rough, which is to be expected with the 4.7 V8. I think if anyone were to drive it, they wouldn't know that the engine was misfiring. We'll see if this works. Keep you all posted. I don't know what to do if the engine light comes back on. I am running out of ideas and will likely need to take it to a Jeep dealer or any good Jeep mechanics in the Nashua, NH area. If you know of any, let me know.

if the rocker arm fell off it would not make noise..this is from experience..we had a ram 4.7 with a misfire at times would run fine for days then skip. removed valve cover and rocker arm was laying in the head. not only that the misfire was for cylinder#2 ans the rocker arm fell off from cylinder #4.

Most of the slipped rockers I've seen didn't make any noise and none of the broken valve springs did! The 4.7's are a little on the rough side for idle quality but if it throws a code there's definetly something amiss. With your short drive daily maybe you have some carbon buildup? I never trust a resistnace check on an injector or coil either no offense. It's fine if it's proves it's excessive or open circuit but a static test like that doesn't show how the windings can fail when induced and the solenoid can operate fine but still not spray fuel enough or correctly! I'd pull the valve cover or swap the injector to another cylinder.

As luck would have it, the engine light came back on last week throwing the same P0301 code. Checked the rocker arms and they were fine. Also checked the compression in each cylinder and they were all good. I changed out the fuel injector for cylinder #1 and drove her all weekend and so far the light has not come back on.

After replacing the fuel injector she ran great for a week. Took it all over the place and this morning the engine light came back on throwing the P0301 code yet again. Any thoughts? Do I take it to the dealer or cut my losses and trade it in?

I'd get it diagnosed and proceed from there! Maybe to early to trade it unless it needs engine work or soemthing similar

Brought it to the dealer last week to have the code diagnosed. The certified Jeep mechanics told me that they could not find what was wrong and what was making cylinder 1 misfire. They told me that they would continue to look at $89/hour with no guarantee that they would find anything. Given that they have already looked at it for hours and couldn't find anything and didn't have any leads, I didn't feel that it was necessary to continue to pay $89/hour not knowing if they would ever find anything. Does anyone know what would cause cylinder 1 to misfire? There must be something that causes it. I don't understand how even the certified mechanics couldn't figure it out. Thoughts?

It's not likely they can't figure it out just can't figure it out in an hour. It takes more then an hour to perform a compression test, cylinder leakage test, remove the valve cover and check rockers and springs etc. An hour pretty much gets you the code read, the plug inspectted, the coil maybe switched to another cylinder and a road test. We've stated the obvious things in thist thread that will cause a cylinder misfire. Im still leaning towards an engine isue at this point without seeing the vehicle it's hard to determine. And having the vehicle 2 days but being billed 1 hour doesn't mean they spent more then 1 hour working on it.