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Unread 08-02-2012, 09:03 PM   #1
Che88
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1988 MJ Comanche 
 
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Location: Raleigh, North Carolina
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88 Comanche Stalls

Hey there, My first post - I've seen several posts about Jeeps stalling, and I know it's a common problem, but I feel like there is more than one thing wrong with this one.

I bought it yesterday, and the body is sweet, but it stalls every time it coasts or when I hit the brakes. Sometimes it won't start (it does crank), but an hour later it will. I plan to change the valve cover gasket, all vacuum hoses and the CPS. The intake manifold and the gasket and all bolts are really rusty, and I can't imagine the seal there is very good. I also bought a fuel filter and changed the oil yesterday. There is excessive blow-by to the air filter, which leads me to believe the major problem is vacuum.

I pulled the EGR today and it is shot. I plan to go to the local EKQ in the morning to find some parts. Also, the charcoal canister is in the engine bay, but disconnected. ???

Thanks for any help, I muchly appreciate it!
-April

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Unread 08-03-2012, 07:44 PM   #2
Che88
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An update; today I replaced the EGR and MAP sensors with ones from the junk yard, and the CPS, new from the parts store. I changed the air filter and re-attached the charcoal canister which had been disconnected with it's hoses dangling. The CPS cable was all chewed-up in the middle.
I had the battery tested and it showed "good". I checked the mounting bolts on the valve cover and intake manifold. They are secure, but I plan to change the gaskets later anyway. I thought I had a fuel filter, but don't, and my husband will pick that up tomorrow along with the brake rotors.
I started it up and it ran okay in the driveway, still idling inconsistently, but we drove it around and to the store a few miles away and back, and no stalling, even when applying brakes, coasting, and stopping. We checked the air filter when we got home and no oil blow-by signs. We are hoping, *fingers crossed* that the majority of the vacuum leak has been addressed.
I don't like the way it's idling but maybe it will get better with the items I have lined up: Valve cover gasket, intake manifold gasket, fuel filter.
Would love to hear any ideas.
Thanks
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Unread 08-03-2012, 09:56 PM   #3
cruiser54
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Here's a homework assignment or two for you.

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


Renix Jeep C101 Connector Refreshing


The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of almost 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before.

Almost every critical signal between the engine sensors, injectors, ECU, and some to the TCU, travel this path through the C101 connector.

The C101 connector is located on the driver’s side firewall above and behind the brake booster. It is held together with a single bolt in it’s center. To get the connectors apart, simply remove the bolt and pull the halves apart. You will find the connector is packed with a black tar like substance which has hardened over time.
Take a pocket screwdriver or the like and scrape out all the tar crap you can. Follow up by spraying out both connector halves with brake cleaner and then swabbing out the remainder of the tar. Repeat this procedure until the tar is totally removed. This may require 3 or more repetitions. Wipe out the connectors after spraying with a soft cloth.

If you have a small pick or dental tool, tweak the female connectors on the one side so they grab the pins on the opposite side a bit tighter before bolting both halves back together.


Revised 07-17-2012


I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals making sure they haven’t retracted into the plastic holder, and then plugging it back together. There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one. Also be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.

ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then plug them back in. I do this on every Renix Jeep I purchase or work on for someone else.

Revised 07/23/2012
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Unread 08-03-2012, 09:58 PM   #4
cruiser54
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Oh, and this:

--------------------------------------------------------------------
The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

“Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled
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Unread 08-16-2012, 08:17 AM   #5
Che88
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cruiser54, Thank you so much for the excellent list.
We've been working on these items and have most of them completed.
We did get sidetracked, however, since my husband replaced the front rotor/bearings and pads. He noticed that the soft lines should be replaced, and successfully changed the right front, but the left is seized. Actually, they all are. I replaced the brake power booster, and had to disconnect the master from the lines to the proportioning valve. What a nightmare. We've come to the conclusion that we'll need to replace all of the brake lines. Now we're researching upgrades. There is a lot of talk about deleting the "extra" line to the back. I'm ready to order parts, just need to decide which direction to go and find part numbers.
Thanks for all of your help!
-Greasy Lady
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Unread 08-16-2012, 10:58 AM   #6
97_4popper
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Hey, a couple of things.
1st, go over to comancheclub.com and get signed up.
Loads of info over there. Everything you ever wanted to know about these trucks and more.

2nd, post pics. We like pics.

these old trucks are fun and frustrating all at the same time.

Check out my build thread over at cc and you'll see what all I've been through with it. It runs reliably now and I drive it at least once a week. But I still have things to do to it.

__________________
90 MJ 4.0 4X4 5sp LB Pioneer Big Ton.
Truck contains parts from 3 MJs, 2 XJs, 1 TJ and a dishwasher.
http://img.photobucket.com/albums/v1...IMG_0101-2.jpg
Check out comancheclub.com...
My build thread: http://comancheclub.com/forums/viewt...hp?f=7&t=27756
Wifes: 97 TJ 2.5 4X4 5sp 31's stock. . . Slow but; reliable.
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Unread 08-16-2012, 02:07 PM   #7
cruiser54
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Quote:
Originally Posted by Che88 View Post
cruiser54, Thank you so much for the excellent list.
We've been working on these items and have most of them completed.
We did get sidetracked, however, since my husband replaced the front rotor/bearings and pads. He noticed that the soft lines should be replaced, and successfully changed the right front, but the left is seized. Actually, they all are. I replaced the brake power booster, and had to disconnect the master from the lines to the proportioning valve. What a nightmare. We've come to the conclusion that we'll need to replace all of the brake lines. Now we're researching upgrades. There is a lot of talk about deleting the "extra" line to the back. I'm ready to order parts, just need to decide which direction to go and find part numbers.
Thanks for all of your help!
-Greasy Lady
Glad to help. There's more where those came from. Enjoy your Jeep.
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Unread 08-17-2012, 09:53 AM   #8
Che88
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Ain't she a beaut, Clark?
che.jpg  
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Unread 08-17-2012, 10:02 AM   #9
Che88
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I signed up for an account over at Comanche Club, awaiting approval. Will commence research on brakes post-haste!
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Unread 08-17-2012, 10:43 AM   #10
Che88
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okay, so I'm looking into switching out the prop valve. I thought they didn't make these new, but found some at summit racing. Is this going to work for me, or do I need to switch to an adjustable valve for an XJ? Do I need to upgrade the MC as well? Mine seems fine.
http://www.summitracing.com/parts/CLP-PV-2/
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Unread 09-01-2012, 01:33 PM   #11
Che88
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Alright, today is the day, finally.
I have pulled all of the brake lines from the truck, except for the line to the load/height-sensing valve, which I have capped on both ends, and am leaving in just in case anyone ever wants to hook it back up.
I pulled the metering block/proportioning valve and cleaned it out, and am ready to flare new lines to the front and rear brakes, minus the load-sensing valve. I have read many conflicting opinions on which port to plug. I know for a fact that the front port on the nose of the block is the one that went to the valve and have a plug for it, but Eagle has specifically said to use that one for the rear brakes and plug the bottom-front one. Is there a difference in the amount of pressure that will go through the different ports? I just can't make the lines until I know for sure.
Eagle! help!
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Unread 09-04-2012, 01:04 PM   #12
Che88
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Below is a message and response about the above post. We made (flared) all-new lines for the Comanche on Saturday, and when we got to the valve, decided to use the old one after opening it up and cleaning it, instead of the XJ one I'd ordered online. We were out there for 13 hours hanging out and working, and at 1am got it all together and commenced bleeding. At the last caliper, I checked the master reservoir level, and glanced at the valve, and WOULDN'T YOU KNOW IT - it was leaking fluid at the sensor on top.
So, we'll be replacing the valve as soon as it comes in. But, I got great advice, and we will have it all hooked up properly so soon. I just can't wait to drive it!

"Che88 wrote:
Hey there, I'm a newbie, and your expertise has helped me a ton already, but I'd love to hear your opinion. You've said more than once that when eliminating the rear load-sensing valve (which you don't recommend, I know) to use the front "nose" port when re-connecting the rear brakes. This is the line that went to my valve before - Why should I use that instead of the bottom-front one? Is there more pressure going through the front than the bottom?

Thanks, I really appreciate you!

my thread:
http://www.jeepforum.com/forum/f53/88-c ... s-1400864/
The reason is that the bottom one normally doesn't provide any fluid or pressure to the rear brakes. Search up the photo I've posted of an MJ distribution block (I call it that because that's really all it does) cut in half. Under normal conditions, applying the brakes sends fluid and pressure to the rear through that front ("nose") port. The one on the bottom is blocked off by the shuttle valve that controls the brake warning light.

If you lose the front brakes, then that same slider that turns on the brake warning light switch also opens up a bypass to allow fluid and pressure to go through the bottom port, which is connected to a second hard line that bypasses the rear height sensing valve. That gives you full braking power to the rear wheels, even if the truck is unloaded and the height sensing valve would be allowing only a small percentage of braking power to the rear wheels.

BTW - I think you have me confused with Hornbrod. I **DO** recommend eliminating the rear height sensing valve. I've had one explode under panic stop conditions. After that happened, I just don;t trust them. Now -- you have to understand that if you bypass it, you WILL have 100% brake power to the rear wheels at all times. In rain or snow, especially when the back is empty, this can result in the rear wheels locking up before the fronts, and that usually makes you spin out. If that's going to be a problem for you, I suggest using a Wilwood or Mopar manually-adjustable proportioning valve for the rear wheels. For myself, I'm an old fart who had been driving for probably 15 years or more before I ever encountered a rear proportioning valve -- and that was in a friend's car, not mine -- and the first thing we did was to get rid of it because it didn't work. I EXPECT the rear wheels to lock up first in slippery conditions, I've trained myself to handle it, and I drive slow enough under such conditions that it's not an issue.
Sent: Sat Sep 01, 2012 5:10 pm"
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Unread 09-09-2012, 08:34 PM   #13
Che88
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All done! The valve we'd re-used blew just as we were bleeding the last caliper, so we had to order a new one and install it yesterday. The parts guy at the dealership gave us the wrong part, one for a Cherokee, but we used an adapter to use the 1/2" port with our 3/8" fitting for the rear line. We drove it straight to the dump, finally able to use our "work truck" for work.
I'll take some photos of the shiny new parts asap.
Thanks for all of the help, fellas!
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