05 4.0 loss of power

Rubicon0572

New Member
Joined
Oct 22, 2023
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8
Location
Reno,nv
After 2 years I’ve gotten my 05 LJ back on the road after another OPDA failure. Before I tore this motor down 2 years ago it had a MAJOR loss of power, wouldn’t even reach 45mph. Now with everything back together its still acting the same way. I have replaced the TPS,IAC, and have adjusted the cam sensor to be in phase with the crank sensor. Small improvements but still not what it should be. I am at a loss because there is no engine codes to go off of. The only thing that I am unsure of is all the o2 sensors are reading in the 2.5v-3.2v range. Does this seem right? I’ve read that older models run under 1v but I cannot find anything 05-06. The upstream cats were replaced within 10k miles. Any input or suggestions would be great. Thank you!
 
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Even with the upstream sensors showing the same? I’m afraid of a pcm issue.

I confess my ignorance of all things not a 97...when Jeeps were simple.

Start with new NGK/NTK/Mopar O2 sensors.

If that doesn't help you can check with @Wranglerfix for a PCM issue.

But loss of power and bad O2s generically means plugged cats.

Hopefully someone with more experience will chime in!

-Mac
 
A manual transmission has three main faults. O2 sensors, loss of gauges and stalling while driving. Get the jeep up to operating temperature and gently tap on the pcm and see what happens.

You can also send the pcm into us and we can run it in our Jeep.
 
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A manual transmission has three main faults. O2 sensors, loss of gauges and stalling while driving. Get the jeep up to operating temperature and gently tap on the pcm and see what happens.

You can also send the pcm into us and we can run it in our Jeep.

Thank you for the response Mark, jeep is a manual trans. There is no codes. Runs very smooth just has less power than a 4cyl with 37s and 3.55 gears. The readings from the o2 sensors make me think there is an issue with the computer but I am going to try and rule them out first.
 
One Jeep or three or four?

One of these days I'd love a writeup or video of your test rig.

-Mac

Here is our research and development department. I am working on some new videos at the moment and should have some within the next few weeks.

A3451DE1-0B88-4617-A0F0-437A9211D882.jpeg
 
I'd drive it around the block and check the temp with a laser thermometer above and below the cats to see if that gives you any indication.

I know you said only 10k miles, but a long time ago I had one of the factory cats on my '06 fail when it only had 15k miles on the Jeep. It feels like you're dragging an anchor.
 
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I'd drive it around the block and check the temp with a laser thermometer above and below the cats to see if that gives you any indication.

I know you said only 10k miles, but a long time ago I had one of the factory cats on my '06 fail when it only had 15k miles on the Jeep. It feels like you're dragging an anchor.

I’ll check them again, when I checked yesterday I had outlet temps about 70* hotter than inlet temps.
 
Even with the upstream sensors showing the same? I’m afraid of a pcm issue.

Just checked some data logs on my 05 6 speed.

I understand how o2 sensors function and their purpose at a fundamental level but don't know the technical aspects of them, but... my NTK upper o2 sensors switch between 0-0.9 volts in closed loop and a pretty consistent 0.9v in open loop.

I don't know if the values you're seeing can be trusted depending on if you're using a good reader or a budget wish bluetooth reader. I would have thought anything outside of normal o2 operating range would immediately throw a code.
 
you can pressure test the cats by taking off a upstream O2 and putting a pressure tester on it.
Clear cats are 3 to 5 psi. clogged will be 8.

You can also just remove the upper O2s as a test and see if the power picks up when the exh has somewhere to go. Of course it will throw codes for the missing O2s.
 
Just checked some data logs on my 05 6 speed.

I understand how o2 sensors function and their purpose at a fundamental level but don't know the technical aspects of them, but... my NTK upper o2 sensors switch between 0-0.9 volts in closed loop and a pretty consistent 0.9v in open loop.

I don't know if the values you're seeing can be trusted depending on if you're using a good reader or a budget wish bluetooth reader. I would have thought anything outside of normal o2 operating range would immediately throw a code.

Values are shown on a high dollar snap on reader