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Unread 07-05-2012, 06:05 PM   #1
aldersonfilm
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1998 TJ Wrangler 
 
Join Date: Jun 2012
Location: Pasadena, CA
Posts: 177
Engine "skips" on some bumps.

So my XJ has started doing a funky thing, like they do... Sometimes, when I hit a bump on the road, the engine cuts out for less than a second. It's just a quick skip. It also sometimes does this when accelerating from a dead stop. I get up to about 1000 RPMs, it skips, and then continues like nothing happened.

Any ideas? Someone said cam shaft position sensor.

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Unread 07-05-2012, 07:29 PM   #2
Paradise XJ
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1990 XJ Cherokee 
 
Join Date: Jan 2007
Location: Paradise, CA, Northern California
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Sounds like something is loose, like a battery connection...or a ground. Only jarring loose when you "hit a bump". Do you have trouble starting it?? CPS is not the panacea...unplug it, clean the connectors, plug back in.

Do the same with battery, starter relay. Make sure all your connectors are plugged in and grounds on shiny & tight
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Unread 07-05-2012, 09:08 PM   #3
cruiser54
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1990 MJ Comanche 
 
Join Date: Oct 2009
Location: Prescott, Arizona
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You have no camshaft position sensor in a 90.
Do this:

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
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