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  #1  
Old September 26th, 2021, 10:20
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alexgalexg alexgalexg is offline
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Random loss of power?

Alright I am officially stumped.

Vehicle will rarely and randomly just lose power. Almost as if it's about to stall. It happens maybe once every 1 hour of run time and lasts about 3 seconds so diagnosis is difficult. Only ever had it happen while driving, not at idle. Sounded kind of like a cps so I purchased a dealer one and installed. While I was there I noticed rodents had chewed on the wires for the cps (vehicle connector side) so I replaced the connector and wires as well. I was also gifted a new throttle body with all new sensors off a jeep going to the scrap yard so that's on there too (throttle body and sensors must have under 1k miles). There is no vacuum leak as I recently had a smoke test done in order to confirm my fuel vent tube was bad which has now been replaced.

I have looked for any other mangled wires and found absolutely nothing, I also see nothing suspicious in the obd live feed. Completely out of ideas here, I don't expect anyone to really be able to answer this as none of you can actually come see the thing, but figured I'd throw a shot in the dark.

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  #2  
Old September 26th, 2021, 11:18
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alexgalexg alexgalexg is offline
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Random loss of power?

So.. poking around I did find this. I'm not sure what would have caused this, but I think I replaced this cap and rotor under 1 year ago.

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  #3  
Old September 26th, 2021, 13:18
RCP Phx RCP Phx is offline
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Re: Random loss of power?

My CmPS did this with me up and till when it finally failed, the little sensor had come loose but couldn't go anywhere.
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  #4  
Old September 26th, 2021, 17:42
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Re: Random loss of power?

Quote:
Originally Posted by RCP Phx View Post
My CmPS did this with me up and till when it finally failed, the little sensor had come loose but couldn't go anywhere.
Fixing the wiring for the crank position sensor seems to have fixed my random no start issue. But I suspected the cam sensor once the random stumble and pop wasn't solved. Between what you're saying and the fact that replacing that cap and rotor button did nothing for the lopey idle or random power loss I think it's worth a try. I'll see if I can get my hands on one tomorrow.

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  #5  
Old October 2nd, 2021, 14:25
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Random loss of power?

Replaced distributor and cam sensor. No change

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  #6  
Old October 2nd, 2021, 14:43
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alexgalexg alexgalexg is offline
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Random loss of power?

So I'm not sure what I'm missing here.
Bogs and backfires under accel.

New stuff:
Fuel pump
Catalytic converter
Downpipe
Muffler
Downstream o2
Fuel vent tube
Throttle body and all sensors on throttle body (a gift from someone scrapping an xj they just put all that brand new on)
Tune up with champion coppers
Distributor
Cam sensor
Cps
Repaired damaged wiring harness side leading to cps that was damaged by mice
Injectors from donor jeep
New o2 sensor fuse (was blown)
Smoke test performed

I honestly don't know what I'm missing here. It idles fine it's only under hard accel that I have this issue.

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  #7  
Old October 2nd, 2021, 18:01
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Re: Random loss of power?

So you put in all those parts with no solid diagnosis of the root cause of the symptoms ?


You did use genuine Jeep OBD sensors and NTK O2 Sensors, right ? You tested all the remaining OBD sensors and inspected/tested all their wire harnesses for chafed/melted insulation, damaged or munched on wires, and corroded/bent/pushed back wire plugs pins ?

I don't see a new front NTK O2 Sensor on your laundry list.
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Last edited by Tim_MN; October 3rd, 2021 at 15:55.
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  #8  
Old October 3rd, 2021, 07:30
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alexgalexg alexgalexg is offline
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Re: Random loss of power?

Quote:
Originally Posted by Tim_MN View Post
So you put in all those parts with no solid diagnosis of the root cause of the symptoms ?


You did use genuine Jeep OBD sensors and NTK O2 Sensors, right ? You tested all the remaining OBD sensors and inspected/tested all their wire harnesses for chafed/melted insulation, damaged or munched on wires, and corroded/bent/pushed back wire pin plugs ?

I don't see a new front NTK O2 Sensor on your laundry list.
Front o2 is a Bosch I installed in 2017. Only the coil was a blind throw, the rest were replaced for a reason. Such as the exhaust which the cat was no longer good on and the rest of the Schaub was very rusty. Fuel vent tube had a pin hole ect. The only sensors I can't speak for are the ones on the new throttle body. I don't know if they are dealer or not. But it was a gift, I have my old throttle body and genuine sensors so if something ever comes up I'll buzz that one back in as there was nothing wrong with it. Just old.

Last night I tried one last thing, hard reset and then disconnected both o2 sensors. It ran perfectly fine, so today I connected the sensors back up and took it for a 1/2 hour drive with 2 highway runs as well as lots of winding backroads with hills. It's working fine. I'm going to try to out 10 more run hours on it this coming week and see how it goes. But I'm wondering if it was compensating for a weak pump and restricted exhaust. Time will tell.

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  #9  
Old October 3rd, 2021, 14:53
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SleeperXJ SleeperXJ is offline
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Re: Random loss of power?

Mine was throwing a code indicating Crank position and/or Camshaft position sensor failure.
The harness upstream of the sensor connector had a short. Repaired the harness, that
fixed the issue.
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Old October 3rd, 2021, 14:55
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Re: Random loss of power?

Specifically, the harness upstream of the cam position sensor.
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  #11  
Old October 3rd, 2021, 16:20
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Re: Random loss of power?

Quote:
Originally Posted by SleeperXJ View Post
Specifically, the harness upstream of the cam position sensor.
I appreciate you sharing. I think I have my wiring sorted and the damage repaired. I will definitely check that area if I have further issues

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