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.

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 thdipstick stude 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.Fuel Pump Ground Comanche

If you want to upgrade your ground and battery cables with custom made parts, contact Neal at www.meanlemons.com 

Neal's cables

Revised 02/04/2017

 

21 thoughts on “Renix Ground Refreshing”

  1. Great post; thx for all the tips; much needed Rx for my 90xj.

    I refreshed the dipstick tube stud grounds today; was expecting only sensor grounds at that stud. Surprisingly, the battery negative cable was grounded to the dipstick stud along with the sensor grounds (battery cable not attached to its own stud).

    If this is a mod then it must have been done by a Jeep service tech which makes me think it might be okay or maybe even advisable (I didn’t make the change and I’m the original owner).

    Have you heard of this mod before? Is it okay to leave the battery cable co-grounded with the sensor grounds on the dipstick stud?

      1. Thank you. I cleaned it and left it. Today I followed your second “suggestion” and added a 12″ ground cable between the battery negative bolt and the closest 10mm radiator support bolt.

        With my sensors and battery already co-grounded at the dipstick, there’s now a much more direct and irresistible ground path to the chassis for the sensors. TPS ground resistance measured at the connector dropped by nearly 1-Ohm from 1.7 to .8-Ohms; I’m jazzed! Thanks for the great suggestion.

  2. hey cruiser54, ive been buggin you with some questions lately hope that is alright, i have only about 2 weeks left to fix and recheck all these points so im making a hurry on it 🙂

    ive added an extra ground from the negative battery terminal to the radiator support bar bolt 10mm. by looking up the part number you mentioned to get at Napa https://www.napaonline.com/napa/en/p/MPB781115/MPB781115_0196438759?interchange=1
    this cable at Napa looks A LOT thicker than the one i have installed, i believe the one i installed is 10,12 or 14 gauge its hard to see but i count 18 strands in this wire.

    will this give any trouble does it have to be as thick like the one from Napa ? will the current take the shortest way and use this wire now to start and eventually give troubles cause it might be too thin ?

    marc

  3. I am so put out by my comanche these days..1989 renix 4.0 auto. I have replaced coil..plugs..wires cap and rotar…new battery refreshed grounds..oil change..filters serviced transmission..UUUgghh! finally driving fine on way home and started spitting and sputtering…almost like a backfire up through the manifold…slowly loosing power get it home and each attempt to restart and simply quit wont start at all…replaced the CPS,TPS..new CPS only shows maybe .2v at crank. weak spark..I need help any suggestions..rail has fuel..starting fluid nothing..

  4. I wanted to add That I did remove the thermostat for one day until my pump came in…could that of caused a problem with the temp sensor???? Im frustrated as H#$% and don’t wanna kick any more dents in her since maybe it’s just bad mechanic. Cruiser if anyone can help it’s you sir??

    1. Wow. Lots of stuff done. So, there’s an orange spark instead of a crisp blue one at the plugs? If there’s any spark at all, the CPS is good enough. Too bad you didn’t drill it before you installed it though.
      I’d be suspicious of the coil/ICM. No real good way to test them though. Tip 4 might be worth doing at this point.

  5. thank you for responding this now is a mission if it turns out simplicity ..New coil by the way strong spark going to middle point..made me drop it quick…at this stage I guess fuel pressure or maybe injectors??? although there is fuel at rail..even after starting fluid will not fire for even a second
    new CPS and I will drill it if you think that might help just the actual holes on the sensor itself correct?..but out the box “NAPA” only reads 2v. i appreciate your time Cruiser your the man.. real quick does the CPS connector from the harness have any power coming from it? it reads a flat 0 .

  6. Hi Cruiser. I swapped a ’98 4.0 into my son’s ’90 XJ. Tranny stopped shifting. He has to shift manually now. I suppose this ground would influence the shifting? All I’ve done thus far is adjust the TV cable and TPS. Is/are the grounds a single bundle of wires or several individual wires? What should I look for?

    Thanks, Scott

  7. I’m embarrassed to say but I didn’t pay any attention when I removed the original engine. Are there multiple wires that go to that stud? I’m wondering if I missed one. I understand about ensuring good contact. Thanks.

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