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Strange power lost after weekend overland trip to Sequoia National Park


Kaptainkid1

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Aug 19, 2019
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Recently my Jeep just had all the fluids zeroed out and new parts installed to fix any leaks. Oil change, Tune up too with new spark plugs and refreshed the cooling system. New radiator and coolant. Needless to say she ran fine the 1st half of the trip fully loaded for a overland camping weekend. No RTT yet but 5 gallons gas, 6 gallons of water, 10x10 pop up, ARB fridge, camping gear and supplies.
I was going up to Lloyd Meadows via 14, 395 to 178. This route is all inclines up to campsite. Fully loaded and done this trip before in my rig seems to have better power going up hill the first half of the trip. I felt the engine oil, gear oil, diff oil, tcase oil and transmission oil changes made difference and freeing up some power.
Once at the campsite the Jeep sat all weekend.
So here is the strange part coming back down and driving down the 395 the Jeep struggled to maintain 60 mph eventhough days earlier I was doing 70 mph going up hill on 395. Also my rig was lighter too. No water and gas in my external tanks. They were empty out to save weight.
Only issue I found on the Jeep after getting home the next day was one back tire was 20 psi and the other 3 we're 26 psi. I aired down 1x time to do a fire road. I must have not filled all the tires correctly. Starting on the trip my tires we're filled to 32psi all four. Can the low air in one tires contribute to going slower on the highway? The rest of the ride home seems to be low in power in passing and getting on the highways. So the second half of the trip the Jeep seems to loose power. 80% of the trip was above 3500 feet to about 8000 feet at campsite.
I know altitude can kill the power but why going up the first day I didn't feel the power loss?
Can anyone help me pin down this possible problem. No check engine light.
2002 TJ, 4.0l, 5 speed, 3.73 gears, 31 tires, 170k miles. 87 octane the whole trip.

20200626_135321.jpg
 
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pagrey

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Not the tire pressure for sure. Run a tank of gas, I've gotten some bad stuff. Hopefully nothing serious but you'll get a code if it is. Nothing like getting on the 395 out of the city, sounds like a good trip.
 
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Kaptainkid1

Kaptainkid1

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I'm going to do a compression test next and check the condition of all the cylinders. I know dry test should be 140-160 psi. One my other concerns is the age of my Cat. It looks like the original and I have 170k on it and they seem ok since I do not have any check engine lights.
I did have a stuck fuel injector 6 months ago. I ran it for about 20 mins to drive it home while shopping. It was 1x injector and it was spilling gas down the exhaust. After changing it out it ran fine. I assume the Jeep was fixed and didn't have any damage. Is this a possible concern? Could my cats be getting clogged? Right now the Jeep is driving fine but it feels down on power. I'm guessing maybe 20 whp loss. It strange because the loss power happened on a 5 hour drive home.
Will do these test and see if I have any strange results.
 

Flivver250

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Cats do get clogged and go bad, that is why it is easy to find replacement parts. You are smart to run some basic checks like you are doing. Compression is good to know for many reasons, but unless there was a sudden component failure, it is not likely to go bad in a week. A component failure is usually accomanied by bangs, screaching, smoke and general distress. When in doubt, put fresh fuel in and flog the shite out of it. It might get better fast or abruptly worse.
 
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Flivver250

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BTW, when I replaced my entire exhaust my Jeep ran much better and noticiably cooler, it had been cobbled together by the vivisectionist PO with no cats at all. Installing the pre cats and main cat along with all new pipes and muffler helped considerably. Even an archaic design like the 4.0 can be fussy.
 
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jodomcfrodo

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Sounds like a cat to me. Internal engine issues are unlikely since you drove it home. Compression is probably fine. Not too many things just abruptly rob TJ’s of power besides the cats.
 
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toximus

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Any chance you filled up with gas at some point during the summit? Maybe it was bad gas?
 
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Kaptainkid1

Kaptainkid1

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Any chance you filled up with gas at some point during the summit? Maybe it was bad gas?
I got gas at Mobile at Kernville River and only filled 9 gallons plus I had 2 week old gas in my Jerry cans. Jerry can gas and gas tank gas ran fine for the previous weeks before I put rest in to the Jeep to drive out of the national park. I guess I could have gotten bad gas but it strange because the Jeep ran fine until I started to drive hard on the highway. It was at least 70 Miles of mountain roads going slow and no signs of bad gas then. I will drive the Jeep to empty too and put in fresh gas and see if that makes a difference. I really hate that this Jeep doesn't have a typical fuel filter on the fuel line to replace. I generally changes those on my other vehicles and they seem to be important part on most cars.
 

Lou

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You jeep just couldn't handle all that camping... Errr I mean overlanding.
 

CharlesHS

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Since you havent received any codes I would guess your MAP sensor is not the problem and as others have responded... It sounds like either the pre's, primary or both cats....
 
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Kaptainkid1

Kaptainkid1

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Going to Harbor Freight and getting a Catalytic Converter pressure gauge. Hopefully this test will prove it's a clogging Cat. Found a used Cat from a used Jeep with 80k for $350 and get all 3 California certified Cats. New is $1700 from Magna flow. Just dont have the cash for a new exhaust right now. Wish me luck!
 

pagrey

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For my 2004 if it's just the rear you can use the Walker 82701 which is carb legal and about $200. If the fronts are bad the Walker 81815 can be used, unfortunately they are $200 each. That's still less then the Magnaflow if you find a good muffler shop. The fronts normally throw codes when they fail so you might find the rear is bad. You can search all the options here.

https://ssl.arb.ca.gov/AftermarketParts/catalysts