The Mj Is Posessed

[MJeep]

89 4cyl 4spd 2wd shortbed. Yesterday the whole electrical system decided to play a game. Every time I turned on the headlights or hit the brake the radio would cut out for a second then come back. Then it started doing that when the engine would miss. Then it shut off. Now it cranks but won't fire. Key off- radio display is on but no music. Headlights on or brakes on-idiot lights come on, radio and dome lights turn off. There's no exterior lights working at all. And the blower motor doesn't work at all anymore. Anyone have any ideas or schematics on this?? Help!!!!

[TheDirtyJeep401]

Sounds to me like some bad wiring.

[Geonovast]

Check your fuse box to see if the clutch master cylinder decided to piss all over it.

 

Also do a search for Cruiser's ground refreshing.

[AeroNautical]

Here's something that might help you out: http://www.alpinefurniturestore.com/JeepDocumentation/MJs/mj1988electrical_troubleshooting_manual.pdf

It's for an 88, but electrical couldn't have changed that much. I have had a long history of electrical problems with my MJ, however I've managed to fix everyone of them, one being a flickering radio. Have you installed anything new recently, like a cb radio or fog lights? 

 

 

 

Check your fuse box to see if the clutch master cylinder decided to piss all over it.

 

Also do a search for Cruiser's ground refreshing.

This made me laugh more than it should have.

[cruiser54]

     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
 

[MJeep]

Thanks for all the replies. And sorry for the late response. I narrowed it down to the head to firewall ground strap. I tested it and it had 8 ohms of resistance from one end to the other. New strap=no more mj deamons. Haha.

[JFAComanche6]

Check your fuse box to see if the clutch master cylinder decided to piss all over it.

 

Also do a search for Cruiser's ground refreshing.

That would SUUUUUUUUCK

[comanchedude]

Thanks for all the replies. And sorry for the late response. I narrowed it down to the head to firewall ground strap. I tested it and it had 8 ohms of resistance from one end to the other. New strap=no more mj deamons. Haha.

Nice...!   glad to hear you found it.  that's always a nice feeling :banana:

[cruiser54]

Imagine that!!! Congratulations.

 

Did you do the dipstick tube stud also?