Losing power at highway speeds

[Sitting Bull]

Hey guys, I have a 2005 LJ (4.0, auto tranny) that is randomly loosing power to the transmission at highway speeds. The jeep runs fine, no burnt tranny fluid or gear grinding, and no codes. I think a sensor is heating up, but don't want to start throwing parts at it without a probable cause...any ideas?

Thanks!!

 

[Bird]

When you say loosing power to transmission are you saying it's slipping ?
The 42RLE has a ridiculously high OD which causes low RPM'S and can feel powerless.

 

[Sitting Bull]

I've had transmission that slip before and this just doesn't seem like that. I'll be driving down the interstate, everything is good, 2000 rpms or so for 60 mph (don't know that for sure, just using that as an example), then all of the sudden to maintain the same speed, I've got to floor it, engine is revving at like 4500 and I can only go 30 mph. Pull off to the side and restart it and it's fine again.

 

[Chris]

Hmm, sounds like it could be a sensor, maybe a throttle position sensor. However, usually when those things go bad, it will throw a code. You sure there's no codes at all?

 

[CommandoJoe]

I recently had the same problem and it turned out to be one of my pre-cats broke up and was clogging the exhaust. I did get an O2 sensor code first. And my mpg slowly dropped over several months from 12-13mpg down to 8-9mpg.

I ended up just replacing the y pipe with both pre-cats, the main cat, and all O2 sensors - no further problems.

 

[Jerry Bransford]

I recently had the same problem and it turned out to be one of my pre-cats broke up and was clogging the exhaust. I did get an O2 sensor code first. And my mpg slowly dropped over several months from 12-13mpg down to 8-9mpg.

I ended up just replacing the y pipe with both pre-cats, the main cat, and all O2 sensors - no further problems.

The exact same thing happened to me though the original O2 sensors were reinstalled.

 

[Sitting Bull]

That's great guys, how were you able to diagnose it was the exhaust? Just don't want to through that much $$ in it without being reasonably sure that's the problem. Also, I wonder why a cool down and restart works?

Thanks for the info!

 

[Drew]

I did have the clogged cat problem, and it was actually diagnosed as such by dropping about 40 bucks at pep boys to have them check it out. I think it's interesting that you say that after it cools down, it runs fine again. I say it's interesting because that's exactly what my jeep was doing. The shop explained that the cats were in fact clogged, and that when the particles heated up is when it would cause the biggest clog in the cat, due to the heat causing expansion of the particles. So I would have that checked out. I ended up going to an exhaust shop and had them remove the cat all together. Now the issue is resolved. I could of had them clear it out or install a new cat, but I wanted my exhaust to sound more fierce lol. Anyways good luck to you.

 

[Dcovi92]

Did you ever figure anything out OP? I’m having the same issue and have had no luck diagnosing it. Any help would be appreciated.

 

[Steel City 06]

I had a similar problem where the engine was misfiring so badly it went into limp mode, meaning it wouldn’t let me go more than about 2300 RPM or about 30 mph. Turned out one of the catalytic converters self-destructed and clogged the 3rd cat.

 

[Apparition]

I had the cat issue driving back from Moab last year, couldn’t exceed 55 mph. Pull the exhaust and look into the cats.

 

[Dcovi92]

I had a similar problem where the engine was misfiring so badly it went into limp mode, meaning it wouldn’t let me go more than about 2300 RPM or about 30 mph. Turned out one of the catalytic converters self-destructed and clogged the 3rd cat.

I’m not sure that it’s a misfire. More of a slip but extremely random. It happens about once a week but never twice in the same day, never even twice on the same drive.

 

[Dcovi92]

I’m not sure that it’s a misfire. More of a slip but extremely random. It happens about once a week but never twice in the same day, never even twice on the same drive.

You think a clogged cat could cause a random slipping?

 

[Dcovi92]

I had the cat issue driving back from Moab last year, couldn’t exceed 55 mph. Pull the exhaust and look into the cats.

You think a clogged cat could cause a random slipping?

 

[Apparition]

You think a clogged cat could cause a random slipping?

No, it causes back pressure and random misfires that put my Jeep in limp mode.

 

[Apparition]

I’m not sure that it’s a misfire. More of a slip but extremely random. It happens about once a week but never twice in the same day, never even twice on the same drive.

Auto? Have you checked the fluid?

 

[Dcovi92]

Auto? Have you checked the fluid?

It is an auto, and I’ve been checking the fluid daily and everything is where it should be.

 

[Apparition]

It is an auto, and I’ve been checking the fluid daily and everything is where it should be.

I’d start a new thread, seems to be a different issue. I think the new thread would give you better visibility.

 

[Dcovi92]

I’d start a new thread, seems to be a different issue. I think the new thread would give you better visibility.

Cool! Will do! Thanks for the input!

 

[LJMolina]

I've had transmission that slip before and this just doesn't seem like that. I'll be driving down the interstate, everything is good, 2000 rpms or so for 60 mph (don't know that for sure, just using that as an example), then all of the sudden to maintain the same speed, I've got to floor it, engine is revving at like 4500 and I can only go 30 mph. Pull off to the side and restart it and it's fine again.

I am having the same exact issue... driving down streets I feel I have no issues, but once im on the highway, the acceleration is sluggish and hard to keep the speed up. Flooring it at best getting 40mph... and the slightest road incline (seriously 1-2degrees) the OD kicks in at 3500-3800 RPMs. After reading so many posts... I ordered all new catalytic converter to see if it solves my issue.

Did it with yours?