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  #76  
Old March 30th, 2017, 21:14
cherokeefan_1 cherokeefan_1 is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

Have you done fluid/filter lately? Just wondering how much material may be in the pan but that won't really tell much about the converter unless there's aluminum and I'm not even sure that's a common issue with these. The aw4 is one tough tranny. I'm pretty sure mine is original at 376k and still shifts like a champ. I believe the TV cable controls line pressure like on the 700r4 and those are easily burned up by misadjustment. Maybe get a pressure gauge hooked to it also for pressures. Just something else to consider.
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  #77  
Old March 30th, 2017, 21:37
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clydefrog clydefrog is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

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Originally Posted by JohnX View Post
No real reason to run compression wet or dry, or leakdown. Vacuum reading was well within reason considering the elevation. He stated it runs very smooth, so no reason to suspect a weak cylinder.

With that new info, I'd be moving on to fuel pressure AND volume.
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Originally Posted by notamos View Post
Vac @ idle is around 18-20.
I wouldn't rule out a back pressure issue. Whats the vac reading under load at ~2k to ~3k after a few seconds? Idle vac readings rarely show excessive back pressure. I have seen back pressure numbers in the 2-5 psi range that can make these 4.0's feel pretty slow.

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Originally Posted by cherokeefan_1 View Post
Just because a cat was new doesn't mean it's good, especially after 14k miles if it's been overly rich. Get a shop to do back pressure on the cat but if it free revs quick it's probably not the issue. Some sensors are designed for high altitude, same with computer tuning, at least with various other vehicles.
Agreed. I have seen rich running vehicles destroy cats in hundreds of miles, not thousands. 14k IS pretty long if there was a slight issue.

Honestly, if everything else checks out I would do a back pressure reading. Most muffler shops can do it pretty cheap.
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  #78  
Old March 31st, 2017, 13:02
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

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Originally Posted by clydefrog View Post
I wouldn't rule out a back pressure issue. Whats the vac reading under load at ~2k to ~3k after a few seconds? Idle vac readings rarely show excessive back pressure. I have seen back pressure numbers in the 2-5 psi range that can make these 4.0's feel pretty slow.



Agreed. I have seen rich running vehicles destroy cats in hundreds of miles, not thousands. 14k IS pretty long if there was a slight issue.

Honestly, if everything else checks out I would do a back pressure reading. Most muffler shops can do it pretty cheap.
Excellent point
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  #79  
Old March 31st, 2017, 21:40
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

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Originally Posted by clydefrog View Post
I wouldn't rule out a back pressure issue.
Just to add to this, every bent pipe I have seen from walker has been a kinked up mess.
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  #80  
Old March 31st, 2017, 23:06
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

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Originally Posted by notamos View Post
OK. I finally had time to hook my scanner (Torque Pro) up to it and give it a run. Torque has a website available for the runs, if anyone wants to take a look at it.

http://view.torque-bhp.com/ and login w/ my Device ID (351713082230320).
I can't log in there. I am interested in your cruise RPMs. It might be time to borrow a set of 33-inch tires.

Quote:
Originally Posted by clydefrog
Honestly, if everything else checks out I would do a back pressure reading. Most muffler shops can do it pretty cheap.
http://www.secondchancegarage.com/public/186.cfm

There is an interactive chart at the bottom of the page that tells you how to diagnose using an analog vacuum gauge.
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  #81  
Old April 1st, 2017, 07:56
trippled trippled is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

Quote:
Originally Posted by clydefrog View Post
I wouldn't rule out a back pressure issue. Whats the vac reading under load at ~2k to ~3k after a few seconds? Idle vac readings rarely show excessive back pressure. I have seen back pressure numbers in the 2-5 psi range that can make these 4.0's feel pretty slow.



Agreed. I have seen rich running vehicles destroy cats in hundreds of miles, not thousands. 14k IS pretty long if there was a slight issue.

Honestly, if everything else checks out I would do a back pressure reading. Most muffler shops can do it pretty cheap.
You can make a back pressure gauge super easy if you have a vac/fuel pressure gauge. Cut up an old o2 sensor and thread a Barb fitting​into it. Under 2 would be ideal and anything over 5-7 would be bad.
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  #82  
Old April 1st, 2017, 10:31
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

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Originally Posted by trippled View Post
You can make a back pressure gauge super easy if you have a vac/fuel pressure gauge. Cut up an old o2 sensor and thread a Barb fitting​into it. Under 2 would be ideal and anything over 5-7 would be bad.
Doesn't need to, he has torque. It does live manifold absolute pressure. To test for restricted exhaust, run at 2500 rpm for 3 minutes in neutral/park. If vacuum drops, exhaust system is restricted. If vacuum maintains whatever it started as, no restriction.
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  #83  
Old April 1st, 2017, 16:41
Green XJ Jeep Green XJ Jeep is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

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Originally Posted by Hypoid View Post
I can't log in there. I am interested in your cruise RPMs. It might be time to borrow a set of 33-inch tires.
At 60 and in 4th his cruise rpm's should be right around 2225.
A little high but acceptable and shouldn't hurt mileage that much.
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  #84  
Old April 3rd, 2017, 04:52
md21722 md21722 is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

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Originally Posted by trippled View Post
You can make a back pressure gauge super easy if you have a vac/fuel pressure gauge. Cut up an old o2 sensor and thread a Barb fitting​into it. Under 2 would be ideal and anything over 5-7 would be bad.
Some of the gauges kits come with an adapter that goes into the O2 sensor location. Mine does.
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