Charging Issue

[ComancheFan]

I've been having a issue with my charging system in my 4.0 renix Comanche. The jeep charges fine at idle and while driving if the rpms are below 1500. Anything above that and my voltage drops down to 12. I know it isn't a gauge issue because if I'm driving at night I can see my headlights get noticeably dimmer when the voltage drops. I have tried a new alternator and the problem persists. My old alternator tested good at AutoZone. I'm not sure where in the system to even look for a bad ground? Possible a relay? 

[eaglescout526]

Follow cruisers tips on cleaning grounds. Then clean all terminals connector to the alt and starter relay. You want to eliminate as much resistance as possible. Also we recommend to get the headlight harness upgrade so your lights aren’t being powered by a 30 year old switch, but by a relay instead. You should see an increase on the volt gauge but it might not be enough to please you. It also depends on what’s all running too like your stereo, AC, fog lamps, cargo lamp, all the main lights on the outside of the MJ. 

[Ωhm]

Belt routing, correct? Belt tension, correct? New/old belt? Check and make sure that the belt is not just slipping.

[cruiser54]

CRUISER'S MOSTLY RENIX TIPS

RENIX GROUND REFRESHING

OCTOBER 30, 2015 SALAD 72 COMMENTS

 

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.

All the components listed below ground at the dipstick tube stud:

Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition Control Module, Fuel Injectors, ECU main ground (which other engine sensors ground through, including the 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. If the whole stud turns, you can use a 7/32″ six point socket or wrench to hold it so the nut can be removed. Worst case, cut the wires and remove the stud and nut. Install new terminal eyelets on the wires when going back together.  Scrape any and all paint from the stud’s mounting surface where the wires will attach. Surfaces 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. Apply a liberal coating of OxGard, which is available at Lowe’s and other stores. 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, apply OxGard, 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 its intended use and subject to corrosion and poor connections at each end.

• 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. Apply OxGard. 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 with a liberal coating of OxGard.

2 STRONG suggestions regarding the ground system:

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 tail lamp 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.  Add a 10 gauge wire, with an eyelet on each end, from that grounding point to a bolt on the frame. Better yet, on both Cherokees and Comanches, complete Tip 29 for the best fuel pump grounding. Be sure to scrape all mounting points to bare metal and apply OxGard also.

If you want to UPGRADE YOUR GROUND AND BATTERY CABLES with custom made parts, contact Paul at www.jeepcables.com 

Revised 02/04/2017

 

[cruiser54]

You really need to complete Tips 1 through 5 at www.cruiser54.com first. I posted Tip 1 above in it's entirety since you said you had no clue on the ground locations. 

Go to the website for Tips 2 through 5. 

[zomeizter]

11 hours ago, Ωhm said:

Belt routing, correct? Belt tension, correct? New/old belt? Check and make sure that the belt is not just slipping.

^^This^^

[ComancheFan]

Thanks for the replies. I'm going to start with upgrading the stock wiring with the Big 7 kit from Paul. It's definitely not a belt, I can see how not charging at higher rpms would make it seem likely. While watching the installation video on the big 7 I noticed the alternator positive wire goes to a relay box just behind the battery that then distributes the power to the rest of the jeep. I think I remember my jeep not starting in the past and tapping on the box made it start it's been a while so I can't remember if it's same box.