weird power problem..... (I know, crazy right)

[starkizer]

My MJ is my daily driver but I only drive a few miles a day. Well, I've started to put more miles on it and drive on the highway more. Tonight I noticed at full throttle against the wind trying to stay at 70 mph giving her all she's got etc etc. Basically pushing her harder then I ever have. The blower fan for the heater would lose power. it was just on vent as I have no factory a/c. It also seemed like the dash lights kind of dimmed in and out ever so slightly. Maybe a bad ground? Think the 2 problems are connected? I know, electrical problems on a Comanche?!?! Unheard of! :P. Thanks as always!

[starkizer]

To clarify, by lose power I mean it didn't blow as hard like it was cutting in and out. Never shut off or anything. And only does it when run at 70+ mph. So no trouble in town.

[Comanche County]

Not sure about the loss of engine power, but the other symptoms you listed sounds like the alternator is getting weak or the belt could be slipping. Do you have a voltmeter or idiot gauge? How's the battery condition?

[cruiser54]

Just for fun, check the ground cable that goes from the firewall to the back of the head. Using a 15mm wrench, remove the bolt holding the cable on to the firewall. Scrape the paint off the firewall down to bare metal where the cable attaches. Polish up the cable end and reattach securely.

[cruiser54]

Double post. Ooops.

[starkizer]

My belt is in bad shape. I think the fan pulley it wraps around is off set. It pulls it off and splits a rib off it. My other MJ did the same thing. Battery is just a year old but there is some minor acid build up around posts. I will check the negitive to the motor. Thanks for the tip. I will post again if that doesnt solve it. Will also have all electrical systems checked at work.

[cruiser54]

My belt is in bad shape. I think the fan pulley it wraps around is off set. It pulls it off and splits a rib off it. My other MJ did the same thing. Battery is just a year old but there is some minor acid build up around posts. I will check the negitive to the motor. Thanks for the tip. I will post again if that doesnt solve it. Will also have all electrical systems checked at work.

 

 

Just do the cleanup of the ground at the firewall. You're not gonna SEE the problem.

[starkizer]

Yeah, I realize I can't see it.... It is covered in grease so I imagine cleaning it up and sanding then connection will help loads. Alt, bat, and starter all check out fine btw

[starkizer]

Went to take off the negative cable, all the insulation crumbled! Had a good two inches of completely exposed copper wire. Took forever to get that bolt off to change it out. Then another forever to take the nut off the stud that was supposed to stay in the motor! I bet this solves a lot of issues though. Thanks all. Will post if it still does it.

[cruiser54]

Time to do this. Actually it was time a long time ago. LOL

 

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