XJ Random Intermittent Engine Power Loss - JeepForum.com

 
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post #1 of 12 Old 01-30-2017, 04:38 AM Thread Starter
bensimpson1981
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Xj XJ Random Intermittent Engine Power Loss

My 96 XJ and I have a love/hate relationship, I love driving it, it hates to run.

BACKSTORY FIRST: (Mar 2016 - May 2016)
Last year in my first xj I had a cooling system that went on the fritz and had massive overheating issues that melted just about every wiring harness under the hood. So I got a second xj that was in better physical shape but had bad valves. I took the good engine out of the first xj and put it in the second xj. Upon finishing up this motor swap I noticed that my exhaust header had some small cracks so this would be a good time to do a replacement. However, I was working on a budget so I BOUGHT A CHEAP NO NAME HEADER OF EBAY, BAD MOVE!!! It ran great all summer. Then when winter set in it started running a bit rough and in about four days time got really rough and really loud. By this point it had stopped running. I pulled the exhaust header off and the cheap crappy header had cracks up the sides of the pipe and every single weld was blown out. I installed a new one OEM spec made from USA steel. Now it would run barely and very rough, misfire codes, and nothing else.

NOW: (Dec 2016 - Jan 2017)
Multiple Misfire, no other codes, good compression, strong spark, good fuel pressure, so I took a look at the distributor. Cap and rotor were a little warn so I replaced cap,rotor,plugs,wires. Then it kicked misfire and cam sensor code, so I replaced cam sensor and the distributor. That cleared cam sensor code but triggered misfire and crank sensor code, so I replaced the crank sensor too. Now, no more codes at all but still running very rough. Idle between 600-1200 rpm, replaced idle air control, now solid even idle at 780 rpm. Still not running good, every time you let off the throttle while driving the engine would chug and sputter, still no codes, so I replaced throttle position sensor, which fixed that. By now it was doing much better but still having a hard time, kicked codes for upstream o2 sensor, catalyst, and downstream o2 sensor, so I replaced both o2 sensors. That cleared everything but the code for catalyst inefficiency

WHAT NEED HELP WITH TODAY: (XJ Random Intermittent Engine Power Loss)
All last week and the week before I drove it about 14 miles a day, no problems what so ever, cold start, warm start, short trips, long trips, ran like a champ. Then one day, driving down the highway 55 mph it just starts running like a turd the full 7 miles home from work. Get in the next day to go to work, starts and runs fine, runs fine all week then again for no apparent reason runs like a turd for a day, then goes back to running fine.

I will try to post some screenshot of my scanner latter.

EDIT: SCANNER PICS

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Attached Thumbnails
USCAN3.jpg   USCAN2.jpg   USCAN.jpg  

Last edited by bensimpson1981; 01-31-2017 at 11:02 PM. Reason: Upload pics from scanner
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post #2 of 12 Old 02-02-2017, 07:24 PM Thread Starter
bensimpson1981
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Today after about an hour and a half of driving and running great, it tried to stall 3 times while driving down the highway, it stalled and died at 3 stop lights.
I got home parked it ate dinner did some laundry and other stuff.
Went out about 2 hours later and it started right up ran fine for a 45 minute drive.
Then right as I was about to put into the driveway it tried to stall again.

Still no codes other than P0420 Catalytic Converter.
NOTE: Coolant Temp is not a very accurate representation of Engine Temp due to our 20 degree weather.

It seems obvious to me that it is some sort of heat soak issue, something is failing to work properly once it heats up.


Could a bad catalytic converter cause that?

I know that upstream o2 sensor tells the computer how to adjust fuel trim, does the downstrem o2 sensor affect how PCM controls trim or is it simply to tell you the condition of your catalytic converter?

I did notice that when at idle (740-790 rpm) the ignition advance stays around 17 degrees on average most of the time but does sometimes fluctuate between 13 and 24 degrees, Is that normal?
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post #3 of 12 Old 02-03-2017, 06:32 AM
S8NNG8
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Go get a new cat and replace the O2's and it should fix the issue. Shop around though. I had one shop quote me $750, while the next shop charged me $120.

D3<!L!>3D
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post #4 of 12 Old 02-03-2017, 03:32 PM Thread Starter
bensimpson1981
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The o2 sensors are both brand new.
I don't want to continue to put in any parts that are not vital.

Last thing I want to do is spend more money fixing an exhaust system only to find out it did not fix the problem.
It does not seem right to me that the catalytic converter would cause the engine to randomly cut out?

If I can't fix it then I am not going to keep it, and if I am not going to keep it then I don't want to spend any more on it.
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post #5 of 12 Old 02-03-2017, 05:51 PM
S8NNG8
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Well tell the person you sell it to that the cat needs replaced, you just didn't want to.

D3<!L!>3D
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post #6 of 12 Old 02-03-2017, 06:36 PM Thread Starter
bensimpson1981
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Have Some Manors

I probably should have noted in the original post that the cat that is in the vehicle is less than four years old and extremely unlikely to be the problem.

I have 8 different code come up for several different parts, replaced every indicated part and it has not fixed the problems.

There is no reason to believe that throwing another part at another code will fix anything.

PCM's can trigger codes on parts that are functioning perfectly, and PCM's can OFTEN not detect when some parts go bad.

Making assumptions and rude statements is a disrespect to the community as a whole.
If your typing just so that you can read your own words online and feel important, start a blog.

Otherwise, do the entire forum a favor and buzz off.
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post #7 of 12 Old 02-03-2017, 06:53 PM
S8NNG8
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Quote:
Originally Posted by bensimpson1981 View Post
I probably should have noted in the original post that the cat that is in the vehicle is less than four years old and extremely unlikely to be the problem.

I have 8 different code come up for several different parts, replaced every indicated part and it has not fixed the problems.

There is no reason to believe that throwing another part at another code will fix anything.

PCM's can trigger codes on parts that are functioning perfectly, and PCM's can OFTEN not detect when some parts go bad.

Making assumptions and rude statements is a disrespect to the community as a whole.
If your typing just so that you can read your own words online and feel important, start a blog.

Otherwise, do the entire forum a favor and buzz off.
This attitude of yours is not gonna help you get answers. Those of us who choose to help want to share our knowledge from owning and fixing these rigs for years. I happen to have experienced your exact problem. Now if you'd like to beat around the bush and waste your time, have at it. Cuz with the information you've provided, you're either gonna get the same answer I gave you, or you're expecting someone to chase your tail for you.
You got my advice, have fun.

D3<!L!>3D
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post #8 of 12 Old 02-09-2017, 03:10 AM Thread Starter
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On a bet with a friend, I replaced the crankshaft position sensor three days ago and so far running flawlessly. No catalyst P0420 code, no codes at all runs smoother than it ever did.

Just pointing it out one more time, just because the PCM triggers a code does not mean that the part it indicates is bad.

It often indicates symptoms and not problems.
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post #9 of 12 Old 02-09-2017, 08:16 AM
S8NNG8
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I'm glad you figured it out. Now if you'd care to safeguard yourself you could always drive it to a muffler shop and have one of the techs listen to it while it's running they could at least give you an idea if the cat is bad or close to it. It's free and then you'd know. Not to push the issue to say I was right, but just so you'd know for sure. If it is plugged it'll waste alot of gas. Being that you're not in a moment of desperation, it would be a good time to patiently shop around for a decent price. It just seems odd that you'd get a cat code and not a CPS code.

D3<!L!>3D
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post #10 of 12 Old 02-09-2017, 09:50 AM
rubicon17
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Quote:
Originally Posted by bensimpson1981 View Post
On a bet with a friend, I replaced the crankshaft position sensor three days ago and so far running flawlessly. No catalyst P0420 code, no codes at all runs smoother than it ever did.

Just pointing it out one more time, just because the PCM triggers a code does not mean that the part it indicates is bad.

It often indicates symptoms and not problems.
hey, what brand did you use? i have one i got awhile ago but it is not a mopar one i think it was a crown.
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post #11 of 12 Old 02-09-2017, 11:41 AM Thread Starter
bensimpson1981
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I just used a crappy BWD from O'Reily's so I don't plan on it lasting to long, based on some of the stuff I have read.

I plan to replace it again this summer with an actual Mopar.


My buddy that I made the bet with, gets 17+ MPG, I am getting around 14 MPG, I imagine that the catalytic converter is the culprit behind that particular problem.


Good advice getting the tested, I am going in on my lunch hour today to have it tested.

I plan to look into replacing it this summer as well regardless, now that I now the engine is still running good.

Got to have it running rock solid before hunting season.


Oh, I lost the bet by the way, I said no way is a cat code related to the crank sensor, and he nagged until eventually the bet was borne.
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post #12 of 12 Old 03-18-2017, 05:49 AM Thread Starter
bensimpson1981
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Update:

I replaced the crank sensor again, this time with a Mopar and instantly noticed a difference in how it runs. Much smoother idle, drives smoother, I know it has been said a hundred times all over these forums but I have to say it again, if you are buying a sensor that is not a Mopar sensor then you are wasting money and asking for problems.

After installing the new Mopar crank sensor and a full month of flawless driving the stalling problem resurfaced, no codes, so a mechanic friend agreed to take on a little charity work and fixed it for free and only took him three hours. He hooked up leads to all of my sensors, injectors, and plugs to an osciliscope and graphed them and was able to determine that all of the electric system were operating flawlessly and that the problem must be mechanical. His graphs were able to locate the problems in cylinders 3 & 4.

Long story short lazy valves on 3 & 4 due to bad lifters.
Since then, been running flawlessly for about two weeks, sounds, feels, and drives like a whole new vehicle.
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