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Major loss of power when hot

mikerhyne

NAXJA Member # 1375
Location
Aurora, CO
Rig: 98XJ, AW4, 177k, 5" lift, 4.56s and 33s, stock under the hood.

So the other day I took the jeep for a longer drive on a hot day since I suspected my radiator was not cooling great to test it and something else weird happened. Once I got it running good and hot 216-220 range without AC at highway speeds all of a sudden it lost most of it's power to the point where I could not accelerate on anything other than flat under about 40MPH. It didn't sound like it was missing, no backfires, it did sound like it had a cold air intake on it when it bogged down as it was louder and it sounded like it was a louder intake noise. I pulled over thinking something was loose and could not find anything and limped home. Anytime it was over about 2100 RPMs if lost most power and I had to nurse it along below those RPMs.

Yesterday I tried to reproduce it and I couldn't but I didn't get it as hot or drive it as long. I did not find any intake leaks either.

It is not throwing any codes.

Recent changes
-Reman alternator - the factory one was having low voltage output
-Coolant temp sensor from Autozone - gauge was not working at all before
-Map sensor from Autozone - was having the occasional hesitation and this solved that

Clearly it is running hotter than desirable so I will go get a factory radiator for it this week and put on a trans cooler too. I may grab a factory coolant sensor too.

What else should I check to avoid repeating the power loss and getting stranded somewhere? I have some ideas but figured I'd ask for you help to help me decide what to check or replace first.

Thanks!!
 
Cheap crappy Chinese engine sensors and hard parts with a "Lifetime Warranty" are well proven to be faulty or even failed right out of the box. Often they are out of specification and provide faulty data. Genuine Jeep sensors are accurate and reliable and will provide the correct data to make your Jeep run right.

I would suppose that a sensor is affected by the heat and shorting out or providing erratic data. I would suspect the IdiotZone sensors, and the TPS. Electrical connections and to a lesser degree wire harness connections are also affected by heat which increases resistance. Make sure all the battery/alternator wires and wire connections are clean, tight, and in top condition.
 
Thanks for pointing me at the cat!

I tried to pull it and everything is too rusted since it is original so now I need to decide how much of it I'm going to replace and let it soak in PB Blaster to see if that helps.
 
Okay so I put on a Magnaflow cat and Dynomax cat back and I think things are running hot in a different way. After about an hour on the highway without AC at 75-80mph I was running 210-215. With the AC on it got up to about 223 on hills but would cool back off. I didn't have the sudden loss of power. After getting off the highway and cruising at about 45 it stayed around 214-216.

These temps still seem to high and now I'm thinking a new radiator or should I look at something else?
 
Sounds normal to me.
 
220-230 uphill with the A/C on is warm, but not overheated.
 
In the summer mine stays between 220-230 ish no matter. I just noticed you're in the northern part of the country. Has the temp been hotter than usual? I'm in southeast Pa so the heat and humidity is or could be the difference.
 
Those temps are a little high, not bad but definitely a little high. The sensor could be off a hair, point an IR temperature gun at the thermostat housing and compare it to the gauge reading (or read the ECM if you can)
 
I'll go pick up a thermo gun today and see if the Autozone sensor is right or not.

Thanks!
 
I'll also add that the jeep hovers at about 195-200 for quite a while if you are driving mildly until you hit the highway and build up some heat then it stays hot.

The day I had the loss of power it was pretty hot for Denver at about 92 yesterday it was about 80 when I was doing my tests. I'm going to get an IR gun and repeat my tests again today.
 
Replace the wire ring terminal at the 2 ground wires that are on the threaded stud
that holds oil dipstick tube bracket on to the block. Nip it off. Add approximately 4"
of extra length of wires (pigtails) to those ground wires to relieve the strain (tension)
on the original wires as they are rather short. Do not just crimp the wires on to the
new ring terminal - solder all the wire splices, and wires at the new ring terminal.
Use heat shrink tubing on all splices and at the ring terminal after you're done.

Why should you do this? Because the 2 ground wires at that ring terminal are the grounds for both O2 sensor heaters, and for the fuel injectors. Those wires are only
crimped on by the factory. After about 17 years of being exposed to heat, oil, dirt,
and water, the electrical contact at the ring terminal crimp becomes dodgy. Heat
from the engine expands that crimp, and then that electrical contact becomes worse.

Also, the length of those wires that comes out of the main loom are a bit short and
so it is subjected to tension and engine vibration. Adding a pair of 4" pigtails relieves
that strain, and soldering the connections and splices assures a much superior
metal-to-metal electrical contact than a mere crimp.

While you're there, you might also want to remove, check, and clean the ASD Relay
(Automatic Shut Down Relay) that is in the Power Distribution Center (PDC). That
relay also controls the power going to the O2 sensor heaters, and the fuel injectors.
 
I'll redo those ground wires as that is something easy to try. So the temp sender seems to be about right based on an IR gun but depending on where I point it in the termo house it can be 25 degrees different. I also discovered that my AC clutch is on it's way out and I suspect that could be part of the issues. It sometimes makes noise that mostly goes away when I turn the AC on. So i need to address that too.
 
I have had awful luck with sensors from Autozone, they seem to buy the cheapest available and are never accurate. I used to have all kinds of "overheating problems" until I started buying Standard brand sensors and switches from rockauto and everything works right since.
 
So I picked up my XJ after having the AC compressor replaced (one of the few things I won't do since I don't have the tools to charge/discharge). So the temperature gauge dropped to 0 on the drive home and then the vehicle stalled and would restart until I coasted into my yard. The noise and drag from the AC compressor is gone for sure and maybe that was my running warm issues. I'm picking up a Mopar coolant sensor and going to check/clean/extend all of the ground wires as needed. It did throw a P0118 code too so I have a sensor or voltage issue. Always something to work on I guess.
 
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