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Unread 03-31-2012, 03:19 PM   #1
srhdog90
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1987 MJ Comanche 
 
Join Date: Mar 2012
Location: winneconne, wisconsin
Posts: 4
87 comanche

I'm having shifting problems with my comanche it will drive and shift fine and then before I know it it will starts downshifting and won't go any higher than first gear... very big problem when you going 55-60 on a highway! Any solutions to my problem? This comanche was a shell until a friend of mine sunk almost 4 grand and rebuilt the whole thing so I'm not sure if any of it is original jeep besides the body and frame.

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Unread 03-31-2012, 06:08 PM   #2
ftpiercecracker
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1990 MJ Comanche 
 
Join Date: Jul 2011
Location: woodbury, Tennessee
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need to ask your friend what kind of auto tranny he dropped in it.
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Unread 03-31-2012, 09:09 PM   #3
cruiser54
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1990 MJ Comanche 
 
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Location: Prescott, Arizona
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Do this as the shift logic ground is at the dipstick tube stud.

Renix Ground Refreshing

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.

The components grounding at the dipstick tube stud are:

Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.

The factory was aware of the issues with this ground point and addressed it by suggesting the following:

Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.

Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.

While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.

Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.

First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4” socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.

A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18” long with a 3/8” lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.

A further improvement to the grounding system can be made using a #4 cable, about 10” long with 3/8” terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.



If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.


Revised 11-28-2011
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Unread 04-01-2012, 08:19 AM   #4
srhdog90
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Location: winneconne, wisconsin
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Cruise54 thanks for the info have you run across this problem yourself ?
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Unread 04-01-2012, 01:57 PM   #5
cruiser54
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Quote:
Originally Posted by srhdog90 View Post
Cruise54 thanks for the info have you run across this problem yourself ?
Yes. Sounds like your TPS may be bad or the dipstick ground is disconnected or poor. The shift logic for the trans controller grounds there as does the TPS.

The ground refreshing is NEVER a bad idea.
Neither is the C101 connector cleaning.
Neither is a sensor ground test.
Neither is a TPS test.

They're all free and need to be eliminated as contributors to your problem.
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Unread 04-05-2012, 07:18 PM   #6
srhdog90
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1987 MJ Comanche 
 
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Location: winneconne, wisconsin
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Well everything you said cruise checked out clean and its still doing the shifting thing now my waterpump apparently blew. After I took it into town. I have antifreeze everywhere it is coating the entire engine compartment even the inside of my wheelwells in the front are soaked. All my anti freeze just poured out from under the truck. Ugh.... man
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Unread 04-05-2012, 10:10 PM   #7
automan2164
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1986 MJ Comanche 
 
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Location: Harvard, IL
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There is a very specific way to bleed a 4.0L Renix to get all the air out of the coolant... Make sure to follow it, or it will constantly overheat.

Rob
__________________
'86 MJ 2.1L 4x4 MT LWB - Factory Diesel
'87 MJ 4.0L 4x2 AT LWB - Metric Ton
'97 XJ 4.0L 4x4 AT Country
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Unread 04-06-2012, 06:54 AM   #8
cruiser54
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1990 MJ Comanche 
 
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After you get your engine bay cleaned up, try this:

Cruiser’s Trans Plug Refreshing


Over near the trans dipstick tube are 2 rather large connectors. One is black and the other gray. These 2 connectors carry all the info between TPS, TCU, NSS, speed sensor, and trans solenoids.
Unplug each one, visually inspect for corrosion or bent pins, spray them out with electrical contact cleaner and plug them back in.

Revised 3-28-2012
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Unread 04-08-2012, 04:47 PM   #9
srhdog90
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Location: winneconne, wisconsin
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Automan its just a little 2.5L
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