2004 Jeep Grand Cherokee Laredo, alternates running great with running rough

DJM

New member
I'm just the driver, so I will be relaying all suggestions to my mechanic .... My jeep can run perfect one trip to work / one entire day and then be mildly to horribly rough running the next day.
On the trips/days it is destined to act up, it starts out running just fine. I sometimes think there is some correlation between driving higher speeds on rough highway as to when it starts to act up.
The rough running is most often between 50-65 mph, but not limited to that range. These last couple of days lower speeds have been an issue too. If I can take my foot off the gas and coast, it almost always goes back to running perfect, altho since it has started acting up at lower speeds, it can idle a bit rough too. Also if I can give it a whole lot more gas and drive a lot faster, it usually runs much less rough. When it's acting up, it has less power (hills / take offs / corners), and gas mileage drops to a depressing 10.5 mg. Now if I have to really put my foot into the gas pedal to get it up to speed, it may shift harder and spew black smoke. It will then go faster and then seconds later have an extra burst of speed without any additional pressure on the gas pedal. Oh, and sometimes the CE light is on (always says an O2 sensor which we replaced) and other times it is not, regardless of how it is running.

Over the time we've spent trying to resolve these issues, it has slowly gotten worse and the problems more pronounced. Here is what's been done:
I added a bottle of Heet, Water remover and injector cleaner to a full tank of gas which seemed to work.
When the problem returned on the next full tank of gas, I added another. Did not help this time.
new O2 sensor
replaced coil pack
replaced injectors
checked for vacuum leaks
replaced a ground wire
checked connections
unplug / re-plug the computer (may or may not make any difference)

This weekend's game plan is to go thru all the wiring with a fine tooth comb. Any suggestions will be greatly appreciated
 
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That black cloud you mention may be your CAT clogging up. Hence the O2 sensor code.

Check your plugs for burning oil or running rich. Might even be a stuck exhaust valve.

I will always suggest cleaning the TB and IAC. And ask if it is the pedal position or the speed/load you are at when it acts up.
Regards,
JPNinPA

Sent using TapTalk
 
Thank you for the suggestions, I will pass them on to my mechanic.

as for pedal position speed / load, there does seem to be some consistency, but not always. I've not been going too far from home with it,
say 30 miles max since it's been having these issues. There are days when it runs great to and from my destination. Other days it might run
rough getting me where ever, but run great all the way back home. On trips when it acts up, it usually starts off great. Then it either seems like a
distance of about 8-10 miles is when it starts to act up, or if I'm driving over a crappy rough road that sometimes seems to start making it act up,
or sometimes it seems to relate to once I am on a highway and wishing to keep a steady speed between 50-65 mph. Taking my foot off the pedal
and coasting smooths it out, or giving it a whole lot more gas, makes it run a bit less rough. Now lately tho, its sometimes been giving me some trouble at
slower speeds too and in this case, taking my foot off the gas does not make it run smooth again.
slower speeds too,
 

I'll ask mechanic which brand he put on it and what the codes were. I dropped it off on my way home as he plans to spend Saturday working on it. Fingers are crossed.
 
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