Chasing Gremlins, The Electrical Kind

[LarryH88bt]

My dad had the truck at the farm and hit a couple bumps, stalled, and would not restart.  Had it towed home, I poked around, jiggled a few wires, would not start.  Jiggled a few more wires and it started fine...  I drove it around the yard a bit hitting bumps and I could not stall it.  I let it run and tapped the ecm and a bunch of other relays, sensors, and harnesses.

 

The fuel gauge doesn't work but every now and then it will start moving.  I've double and triple checked the ground wires for it.  Fresh and clean at the rear tail light and then another closer to the sending unit.  But I have a feeling its the actual sending unit or whatever that thing is that holds the pump in place.

 

The speedo has gone weird after this incident, it will sink further down at idle or going reverse but reads upwards fine. 

 

I need some more heads.

 

 

[Biotex]

Larry, Your post is kind of all over the place. Not sure exactly what you are asking. Have you read cruisers tips?

[LarryH88bt]

Well I'd like to know why it stalled, why it wouldn't restart, and then why it would restart without actually fixing anything.  :???:

[cruiser54]

Well I'd like to know why it stalled, why it wouldn't restart, and then why it would restart without actually fixing anything.  :???:

You may never find out why so you've gotta take some steps.

 

I would do the complete ground refreshing, connector refreshing, and test the CPS. stick or auto trans?

[LarryH88bt]

Ok, I did replace and clean alot of grounds and connectors already but I guess I can do it again.  I'm also going to do the instrument panel refresh.  It's an automatic.

[cruiser54]

Ok, I did replace and clean alot of grounds and connectors already but I guess I can do it again.  I'm also going to do the instrument panel refresh.  It's an automatic.

Gotta do ALL of them. No shortcuts.

 

Here. I'll lay them all out for you. Did you even click on my link? There's photos there.

 

 

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, failed emission tests, and wasted money replacing components unnecessarily.

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.

For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.

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 03-04-2013

 

 

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

 

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 ¼" 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 03-02-2013

[LarryH88bt]

Yeah, this one http://comancheclub.com/topic/36382-cruisers-renix-tips/

[cruiser54]

Yeah, this one http://comancheclub.com/topic/36382-cruisers-renix-tips/

How's it coming along?

[LarryH88bt]

Got through the connections.  Most of them were clean.  Did the grounds including the stuff behind the dip stick.  Haven't found the time for the tests yet.  I'll probably start with just a general tune up and the CPS adjustments.

[cruiser54]

Got through the connections.  Most of them were clean.  Did the grounds including the stuff behind the dip stick.  Haven't found the time for the tests yet.  I'll probably start with just a general tune up and the CPS adjustments.

Good tune-up. Cap and rotor with brass contacts, Napa wires. NGK or champion Copper plugs only.

 

CPS can be tested.....

[Oddmodman]

I had a Geo Storm that had this problem. Hit a bump, died, and then would intermittently die even when I was driving, and sometimes wouldn't start for hours after an episode. Turned out it was my ignition coil (think that's what it's called), got bumped loose and then would lose connection every once in a while. Its fasteners failed.

[1989 Eliminator]

Follow Cruiser's tips... I had a similar problem and his tips fixed my problem. :D