Jeep Garage  - Jeep Forum banner

'04 WJ, bizarre misfire of sorts

7K views 39 replies 4 participants last post by  Lhutter1 
#1 · (Edited)
Hey guys!

Our 2004 GC Limited has a strange misfire issue of sorts... When I say misfire, it sounds and feels like a misfire, however, there's "no" check engine light, no codes. Exhaust appears louder as I'm driving along and there's a distinct one cylinder that stands out as different. You can feel it as well, especially as RPMs hit above 1500 or so, all gears. With my head under the hood it doesn't sound loud at all. It happens regularly when the ambient is below 67 degrees F, only as the engine gets up around operating temp, it's like someone hits a switch and it happens. Cold engine runs great! If the ambient is "above" 68 degrees or so, it runs excellent cold or hot engine.

I've seen many posts about head gaskets and fuel injectors and such, but those all seem like more permanent issues. I took it to a friend's shop and we put a scope on it. No misfires recorded, but it was obviously missing and the engine stumbling and jumping around. The only thing noted out of spec was the IAT sensor was reading 108 degrees "F". I replaced the sensor and it reads ok, but no change in operation. I also changed the TPS. I've also changed plugs. I thought also it may be coils or fuels injectors as they heat up, so I used freeze spry on each with no difference. Besides, that wouldn't explain why it runs good in warmer air... Anyone else seen this?

Thanks!
Lorne
 
See less See more
#29 ·
Your WJ has two O2 sensors on each bank(right and left side of the engine) for a total of 4. The first sensor is before the converter and is used by the PCM to monitor the fuel mixture. The second is located after the catalytic converter to monitor the converter and ensure it is doing its job. I changed the pre-cat sensors on bank 1 & 2 after reading that over time they become less accurate. I also used the factory brand (I forget which brand) as my reading told me the other brands are problematic.
 
#30 ·
Thanks for the clarification. We'll definitely be looking into O2s, sounds like a reasonable thing to change.

Last evening we did an induction cleaning and, though it's still not quite right, it seems to be better. One thing we did notice is the fuel pressure is steady at 47 lbs, ignition on but not running, on and at idle and high throttle. I seem to remember reading somewhere the spec being 50 lbs. How critical is that number?

Thanks,
Lorne
 
#31 ·
One more thought in light of your fuel pressure question... The WJ has two fuel filters. One sock-type is located in the tank on the fuel pick-up. The second is located over the rear diff and has an internal fuel pressure regulator. My hours of reading revealed that the regulator can become less accurate over time. I replaced the external filter/regulator while I will doing my 80k mile service. IIRC that filter was about $25. Rockauto.com has them anywhere between $15 and $30.
 
#32 ·
Ah, good catch! I thought the only filter and regulator was in the tank (less than happy thoughts about changing that! lol). That's an easy thing to change.

I'm not sure how related it is to the stumble/misfire problem, but I have noticed the last week or so, that at cold start there's a little hesitation in the pedal, as if the choke wasn't set quite right (back in the days of manual choke). It doesn't feel like a misfire at that point, but I do have to play with the pedal a bit to accelerate. The colder it is, the worse it is. After a couple minutes of running that issue goes away.

Thanks,
Lorne
 
#33 ·
Been thinking about all the things I have changed on my WJ since I got it in light of my extensive WJ research. It seems you have covered most of them but here is my list for reference:
-Plugs (HO so I replaced the platinum plugs with the same ones)
-External fuel filter/pressure regulator (from napa)
-Throttle position sensor (Mopar)
Those three made a significant improvement in drivability and fuel economy at 80k mile.
 
#34 ·
I did change the plugs, but with NGKs. It did not make a difference in the problem. I do have Champions ready to install, just to get it back to original. I've heard some say that other plugs just don't perform quite the same. I also changed the TPS. It's not a Mopar one. I've heard that can make a difference. Seemed to track the throttle OK with the analyzer, but could still be issue. Fuel filter is cheap and makes sense after 84k anyway. Will have to wait til the weekend to do that one.

Here's what I have done to date...
TPS
IAT sensor
IAT Harness
Plugs
2 coils (bounced them around different cylinders)
Air Filter
BG 44K
BG Induction cleaning
Pulled IAC and spray cleaned along with throttle body

Testing:
Fuel Pressure
Fuel Injector Balance
Disconnected coils one at a time
Used analyzer to view and test as many thing as I could

In the back of my mind I'm wondering about vacuum as well. There's nothing obvious, but along with changing the filter and such, I may start spraying around with carb cleaner or propane or something of the sort.

Thanks!
Lorne
 
#35 · (Edited)
Regarding the fuel pressure, the manual states 49.2 +- 5 PSI, so yours is still within specs. Although i still think its a good idea to change that filter/regulator once in a while, just to avoid problems.
And regarding the O2 sensors, they are OEM from Denso. Eventhough Bosch is making very good O2 sensors, they heat up more slowly then the Densos and for that reason the PCM will set a DTC.
Just put today my jeep on a scanner and when i was doing some of the available tests, i found out that both precat O2 sensor heaters didn´t pass the test. Didn´t get any DTC for that nor higher then normal fuel consumption (ok, that normal is in fact already high :D), but i will probably order some new sensors next time i do need something.
 
#36 ·
Any more updates, Lorne?
 
#37 ·
No updates yet, thanks for asking though... Been swamped at work and the same after work with family stuff, so it's hard finding time to get to the jeep. The weekend looks pretty good though. :)

I did notice that it had that misfiring feeling/sound from the get go this morning. It usually doesn't happen til the engine heats up a bit. I'm guessing whatever it is is getting worse (maybe more easily discovered I hope!)...

Thanks,
Lorne
 
#38 ·
Well, I ended up sick Saturday and Sunday and didn't get to do anything with the jeep. I have 2 Denso upstream O2 sensors on order and should have them tomorrow, so we'll go from there.

Friday afternoon we took a long ride (hour each way) with a few stops around our destination. After a while (40 minutes or so) of running it seems to behave better than in the 20 minute drive to work. After sitting a couple times for 15 minutes or so it was still ok, then a couple times in between it was back to it's old self. The trip home seemed pretty smooth... Weird! Then again, it's my truck! lol

Thanks!
Lorne
 
#40 · (Edited)
Hey guys!

Well, after a very long stint of being quite sick, I finally got the opportunity to change out my O2 sensors. No notable difference. It was warmer (in the 60's) earlier in the week and again, it ran much quieter and smoother. Now it's cold and the Jeep's loud. There's always been a slight bit of stumble to it sitting at a light. Is it possible that what I'm hearing is the broken exhaust manifold bolt issue I've been hearing about?

My thought (and please feel free to tell me if I'm smoking something here) is that maybe the manifold starts off relaxed and pressed up tight to the head. Then after a few minutes of running it heats up (unevenly) and warps and pulls away, creating an exhaust leak on one cylinder. The colder it is, the worse the warpage until everything stabilizes in temperature and sort of un-warps to a point. After running it for better than 20 minutes it quiets down some and runs a bit better. If I shut it off to run into a store or something, it will typically be better after sitting for 10 or 12 minutes.

Yesterday I noticed that the problem started just prior to it going into closed loop mode, as when I got on the freeway it was not warm enough yet to engage overdrive. It allowed OD about 3 or 4 minutes after it started running obnoxious. Is that theory at all feasible or am I going the wrong direction?

Thanks!
Lorne
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top