Solve this... loss of power - JeepForum.com
 
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post #1 of 9 Old 08-18-2012, 09:55 PM Thread Starter
Xanatos
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1991 XJ Cherokee 
 
Join Date: Dec 2011
Location: Hendersonville
Posts: 114
Solve this... loss of power

I've researched my problem some and talked with mechanics around, many suggest different things so I was wondering what you all thought.

So I used to be able to come back from college down from Tigersville, SC to Hendersonville, NC and would make it up with no problem. For those of you who don't know the area, I must drive up the mountain which involves climbing about 1200 feet in less than 12 miles. I used to be able to make it up going in 4th gear at around 2300 rpms without loosing any speed. Lately I have been having to downshift into 3rd gear just over 3000 rpms and struggle to maintain speed.

I don't know when it started losing power and think it has been gradual since I didn't notice the power loss. I didn't go up the grade for at least 2 months, so I'm not sure when it started.

Things that I do know: I have two busted bolts on my manifold. My fuel filter was just changed and full of crap, but did not result in much more power. I recently changed my sparkplugs, on the cheaper end(I think Ford brand). It has lately been idling 300 rpms over than usual. It's a 1991, 4.0, 170000 miles on it. Not sure of any other information that might pertain to it.

If anyone has any suggestions of what might cause this power loss, or what I might try next I would be much appreciated. Thanks!


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post #2 of 9 Old 08-19-2012, 09:11 AM
CJ7-Tim
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Location: out in the garage - Minneapolis
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Lack of proper routine maintenance would be my first suspect. Are ALL your tune-up parts fresh, and top quality parts ? Cheap parts are cheap for a reason. Inspect your exhaust manifold for cracks, and repair or replace any failed exhaust pipes or manifold bolts. When was the last time the O2 sensors were tested or replaced ? Test the Throttle Position Sensor (TPS).

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post #3 of 9 Old 08-19-2012, 10:40 AM
crzmn1
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1998 ZJ 
 
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my exaust looks like that i am going to replace it with a header not much difference in price
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post #4 of 9 Old 08-19-2012, 11:47 PM
Reptile
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1991 XJ Cherokee 
 
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Location: Bakersfield
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A lots of stuff can cause loss of power. Here are a few things:

- Your engine call for NGK plugs. The 4.0 can be sensitive to the type of plugs you're using.
- Refresh your grounds and battery connectors, and distributor. I can't tell you how important this is.
- How old is your air filter. Older than a yr? Replace it.
- Cracks on manifold, upstream of O2 sensor. As Tim mentionned. This will fool your O2 sensor and cause improper air/fuel mixture.
- Check your vac lines to MAP sensor. This can affect idle, performance, etc.
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post #5 of 9 Old 08-20-2012, 07:10 AM
n5xl
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1998 XJ Cherokee 
 
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Location: Colorado
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Good list so far of things that need attention. Further down the list of things to check would be to look for exhaust restrictions (think plugged up catalytic converter). Old wrenches know how to check for exhaust flow issues with a vacuum gauge ...you can check it for yourself if you google how to do it...very easy to check.

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post #6 of 9 Old 08-20-2012, 08:18 AM Thread Starter
Xanatos
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1991 XJ Cherokee 
 
Join Date: Dec 2011
Location: Hendersonville
Posts: 114
Thanks for the list guys! Now I have somewhere to start. I have only owned it since January so I don't know how well it was kept up before, it seemed pretty nice when I got it. Today I will probably change the air filter just so I know that is good. Sometime soon I think I will probably upgrade my plugs, hopefully next paycheck. I was driving yesterday and hit a few bumps and lost tons of power, a friend took a hammer and banged on my catalytic converter which helped regain some power. So today I will also change out my cat... if I can get the rusted bolts out I'm gonna clean my connections hopefully to, is there any type of cleaner that would be useful? or just a good brush?

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post #7 of 9 Old 08-20-2012, 09:07 AM
crzmn1
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1998 ZJ 
 
Join Date: Aug 2012
Location: crawford
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i used baking soda on the battery posts and a wire brush on the rest
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post #8 of 9 Old 08-23-2012, 03:00 PM Thread Starter
Xanatos
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1991 XJ Cherokee 
 
Join Date: Dec 2011
Location: Hendersonville
Posts: 114
I changed my air filter which helped a little bit, but it turns out my cat was very clogged and broken. My muffler was in pretty bad shape also. Since I was not able to get the cat off and I can't weld, I had my mechanic change it out. The difference is night and day... and it sounds freakin awesome now! I'm still gonna get around to cleaning my wires this weekend hopefully because I was looking under the hood at wires and some connections are pretty bad. Thanks for all the advice guys!

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post #9 of 9 Old 08-24-2012, 05:43 AM
cruiser54
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1990 MJ Comanche 
 
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Have you ever checked the level and condition of all the fluids in this Jeep?
I do that right away on any "new to me" vehicle.
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