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  #1  
Old January 10th, 2021, 13:32
Grawl Grawl is offline
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Exhaust acts like itís plugged, but fine on restart

Going nuts with this issue on my daughters 2000 XJ. In the last 5000 miles, new O2 sensors, new injectors, and new plugs. Jeep has an issue where it almost acts like the exhaust is plugged. Starts fine, but drive it a few blocks and it starts losing power to the point you have to pull over and it will hardly idle. Shut it off and restart it and itís fine. Start driving and itís the same issue. No CEL. Just installed a new CAT, TPS, checked fuel pressure which is at about 45, but no luck. Any ideas?

Links to hear what itís doing in video below

https://youtu.be/iLA0Jb1NvY0

https://youtu.be/_qaeH5wxdaE
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  #2  
Old January 10th, 2021, 13:34
Grawl Grawl is offline
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Re: Exhaust acts like itís plugged, but fine on restart

Also checked for vacuum leaks, but all good.
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  #3  
Old January 10th, 2021, 14:55
Lost_Wrench Lost_Wrench is offline
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Re: Exhaust acts like itís plugged, but fine on restart

I think the CPS and Idle Air Control Valve can cause symptoms very similar so look at both. Maybe clean Throttle Body as well.

I'd also put it on a scanner even though your CEL isn't on, just to see.
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  #4  
Old January 10th, 2021, 14:55
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Tim_MN Tim_MN is offline
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Re: Exhaust acts like itís plugged, but fine on restart

Bosch or NTK O2 sensors ?

Genuine Jeep TPS or crappy Chinese clone TPS ?

Tested the CPS ?
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  #5  
Old January 10th, 2021, 15:13
Grawl Grawl is offline
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Re: Exhaust acts like itís plugged, but fine on restart

Quote:
Originally Posted by Lost_Wrench View Post
I think the CPS and Idle Air Control Valve can cause symptoms very similar so look at both. Maybe clean Throttle Body as well.

I'd also put it on a scanner even though your CEL isn't on, just to see.
Will check the IAC. Already cleaned the TB, but forgot to mention. Thank you.

Quote:
Originally Posted by Tim_MN View Post
Bosch or NTK O2 sensors ? Canít remember....they were eBay, so probably crappy ones.

Genuine Jeep TPS or crappy Chinese clone TPS ?
Chines clone. Hoped it would be ok, but Iíll test the new one. Thank you

Tested the CPS ?
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  #6  
Old January 10th, 2021, 15:40
tech1001 tech1001 is offline
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Re: Exhaust acts like itís plugged, but fine on restart

How many cats do you have ? some 2000 had 3 cats and some only had 1 cat . and why did you change the cat ? Was the cat broken inside ? because pieces could be in the muffler plugging the exhaust at time's turning off the engine would let the piece move and let the exhaust flow again . good luck
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  #7  
Old January 10th, 2021, 15:47
Agreen Agreen is offline
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Re: Exhaust acts like itís plugged, but fine on restart

Sounds like tech might be on to something. You could unbolt the exhaust a little and take it for a short drive
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  #8  
Old January 10th, 2021, 17:59
lawsoncl lawsoncl is offline
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Re: Exhaust acts like itís plugged, but fine on restart

IAC should be an issue at anything but idle. In the videos, it sounds starved or plugged, versus a misfire caused by a failing CPS.
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  #9  
Old January 10th, 2021, 18:02
Grawl Grawl is offline
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Re: Exhaust acts like itís plugged, but fine on restart

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Originally Posted by tech1001 View Post
How many cats do you have ? some 2000 had 3 cats and some only had 1 cat . and why did you change the cat ? Was the cat broken inside ? because pieces could be in the muffler plugging the exhaust at time's turning off the engine would let the piece move and let the exhaust flow again . good luck
Quote:
Originally Posted by Agreen View Post
Sounds like tech might be on to something. You could unbolt the exhaust a little and take it for a short drive
It does have the 3 cats. I did the lower just as a ďthrow a part at itĒ as it feels like other vehicles Iíve had that had a plugged cat. It looked fine though, and the tops test out fine with the heat gun/vacuum test. I still might drop the exhaust as Tech recommended just to see if that helps. Seems old though that the issue resets after starting the vehicle. I thought a plugged cat creates starting issues and poor performance always, and that a restart wouldnít change anything?
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  #10  
Old January 10th, 2021, 18:05
Agreen Agreen is offline
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Re: Exhaust acts like itís plugged, but fine on restart

How to test for a bad catalytic converter:
-Hook up a vacuum gauge or scan tool that can monitor vacuum
-idle the engine
-Quickly snap the throttle open and closed.
-If vacuum immediately returns to its original value, the cat is good
-If vacuum stays low (close to zero) for a while then slowly creeps back up, the exhaust has a restriction

Now you can drop the exhaust a little and take a quick drive to confirm it.
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  #11  
Old January 10th, 2021, 18:09
tech1001 tech1001 is offline
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Re: Exhaust acts like itís plugged, but fine on restart

Check to see if the front cats rattle if they do then they are broken inside , it can just be one .
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  #12  
Old January 11th, 2021, 04:48
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Tim_MN Tim_MN is offline
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Re: Exhaust acts like itís plugged, but fine on restart

Quote:
Originally Posted by Tim_MN View Post
Bosch or NTK O2 sensors ?

Genuine Jeep TPS or crappy Chinese clone TPS ?

Tested the CPS ?


Quote:
Originally Posted by Grawl View Post

Chines clone. Hoped it would be ok, but I’ll test the new one......
That the symptoms seem to occur as the PCM switches from open loop to closed loop is suspicious. Having the symptoms "cured" with a simple re-start sort of reinforces the suspicions.

The Jeep 4.0L does not play well with Bosch or no-name O2 sensors, you really do need to use NTK O2's and genuine Jeep OBD engine sensors. Cheap parts are cheap for a reason.


The symptoms don't really suggest a faulty cat.
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