95 4.0 power loss

Iamanidiot

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Jun 1, 2020
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Tomball, TX
Ok so I used to belong to the facebook page but it was shut down in lieu of this forum, and now I am here with an issue that has me puzzled. I have a 95 with the 4.0 (HO). Its struggling producing top end power and even is somewhat weak on the low end. I've replaced spark plugs and a bad alternator for the electrical system (problem existed before this) which did seem to pep it up some. Also I have replaced the fuel filter. The rubber connecting lines had dry rotted and were leaking and after inspecting fuel filter decided it needed changing as well. Well I've noticed two things, not only is my throttle cable seemingly stretched (temporary fix for that did determine it wasnt the power loss issue) but despite gaining some low end pep it refuses to carry the power to higher rpms. Is this catalytic converter? Throttle position sensor? Maybe timing? I'd doubt timing since it idles fairly smoothly for the 4.0s I have encountered. Just very slow revving and does not at all drive like the other 4.0s I have had particularily in cherokees which were often heavier. Some info the prior owner made some changes to the drivetrain mostly beefed it up, I have not researched who or what but it's still Dana family for the differentials. I have 32x11.5s, and the AX15 transmission.
 
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Iamanidiot

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Jun 1, 2020
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Tomball, TX
Tomball? Small world, I was just there an hour ago. Have you checked for any engine codes? If you haven't done it you need to count the blinking Check Engine light after turning the key on and off several times.

Try this: https://www.quadratec.com/jeep_knowledgebase/article-24.htm
I do plan on checking the codes ASAP next chance I get I have a fairly nice code reader. The reason I'm waiting till I get an off day is on my own I couldn't locate the connector. AC vent sits right where the connector normally would be. Of course no check engine light present but I did forget about the key trick. Thanks!
 
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Iamanidiot

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Jun 1, 2020
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Location
Tomball, TX
Tomball? Small world, I was just there an hour ago. Have you checked for any engine codes? If you haven't done it you need to count the blinking Check Engine light after turning the key on and off several times.

Try this: https://www.quadratec.com/jeep_knowledgebase/article-24.htm
Also it really is a small world lol!!! If you ever see a really badly faded black YJ rolling around with full doors and top it's probably me!
 
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Walt Jaquith

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Apr 12, 2020
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Lafayette, OR
Feels like a partially plugged cat to me. Have you done a compression check? Inline sixes will still run fairly smooth with a weak cylinder.
 
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Flyer58

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Apr 12, 2020
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Magnolia, Texas
The part where you mention "changes to the drivetrain" makes me question what differential gear ratio you have with the 32" tires.

Here's a link to show what your RPM should be in 4th gear at 65MPH. Use a phone app to determine the true speed not your speedometer. The diffs may have a low gear ratio and struggling but without checking you'll never know. I'm sure you'll find the speedometer is off just from tire size alone. I have 31" tires and the speedometer reads 5% slower.

Link: https://www.quadratec.com/c/reference/gear-ratio-guide-for-larger-tires

Chart for 65MPH in 4th gear (1:1 ratio)

1a.jpg
 

machoheadgames

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May 19, 2020
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Location
Dallas, TX
I do plan on checking the codes ASAP next chance I get I have a fairly nice code reader. The reason I'm waiting till I get an off day is on my own I couldn't locate the connector. AC vent sits right where the connector normally would be. Of course no check engine light present but I did forget about the key trick. Thanks!
You have a 95. It is not an OBDII vehicle, so it does not have a standard under dash OBDII port. You have an OBDI vehicle, which has a connector for an OBDI scan tool under the hood zip tied to the wiring loom nearby the brake booster. But, it's easier to just use the key because the key will tell you everything the scanner will and it's one less tool to have to mess with. So, after 7 years, this is why I still just use the key trick and it always told me everything I need to know.

As for the problems, did you ever end up reading the codes? Anything show up if you did?

If I'm understanding correctly, this hasn't always been a problem and is now a problem? If it is a problem you've always had, then you may just be experience sluggishness from stock gears on larger tires, but if the problem arose as of late, then it is probably an actual issue developing.