hi...
my first time on this site.. i bought this xj a couple months ago.. nothing but problems.. first alternator and battery died.. replaced them and the serpentine while i was at it.. so i thought it was fine when it first started up drove to auto zone to bring back old alternator.. wouldnt start... had spark and starting fluid wouldnt start it.. til it cooled off.. kept doing this.

its like this thing has a mind of its own... was told fuel filter. changed it. fuel pump. changed it. crankshaft sensor. changed it. still it would start if cold, then if shut off.. no start and would just keep turning over. when i try to start it and it wouldnt start i would also smell fuel under the hood..

so i find a loose ground wire on the motor behind the oil dipstick.. i thought that was it jeep would fire up immediately every time for weeks.. until out of nowhere back to stalling.. so now when it starts if i rev the idle it wants to bog out and die. then after driving out of nowhere it would drive perfectly.. but once again when i shut it off.. wont start again.. this morning was fine.. started up every time and ran great.. went home for about an hour. no start again. and 6 hours later still wont fire.. someone please help me before i drive this thing through the front door of the guy i bought this from!!!!

 

oh i forgot.. its an 87 cherokee laredo I6 4.0

 

Where do ya wanna start? Pun intended.

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
Renix Jeep C101 Connector Refreshing
　
The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of almost 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before.

Almost every critical signal between the engine sensors, injectors, ECU, and some to the TCU, travel this path through the C101 connector.
The C101 connector is located on the driver’s side firewall above and behind the brake booster. It is held together with a single bolt in it’s center. To get the connectors apart, simply remove the bolt and pull the halves apart. You will find the connector is packed with a black tar like substance which has hardened over time.
Take a pocket screwdriver or the like and scrape out all the tar crap you can. Follow up by spraying out both connector halves with brake cleaner and then swabbing out the remainder of the tar. Repeat this procedure until the tar is totally removed. This may require 3 or more repetitions. Wipe out the connectors after spraying with a soft cloth.
If you have a small pick or dental tool, tweak the female connectors on the one side so they grab the pins on the opposite side a bit tighter before bolting both halves back together.
　
Revised 07-17-2012
Renix Jeep ICU/Coil contact refreshing
　
　
The contacts between the coil and the ICU on your Renix Jeep can become corroded and loose causing a complete or intermittent no-start condition. I recommend the following procedure as a maintenance precaution to insure this is eliminated as a possible cause now and in the future.
The coil is attached to the ICU by two T20 Torx bolts. Remove these two bolts and lift the coil up off the ICU. You will see 2 pins and 2 sets of contacts. Clean both the pins and springy contact pieces with a good electronics cleaner.
Squeeze the springy contacts closer together with some needlenose pliers. Apply some dielectric grease to the contacts and bolt the coil back on to the ICU.
While you’re right there unplug the connectors from the ICU and inspect the pins in the harness connector. Make sure the pins are not retracted into the connector. Spray out the connector and the receptacle of the ICU with the same good electronics cleaner you used earlier. Apply dielectric grease to the connectors and plug them back in.
I feel this procedure should be performed at least once in the lifetime of a Renix Jeep.
　
Revised 11-29-2011

 

wow ok.. so it looks like bad grounds would be my main problem then?? ill start checking them all tomoro i hope thats all it is..

 

There are 3 write-ups there. Gotta make sure that stuff is done before you go chasing down any rabbit trails.

 

If it wouldnt start till it cooled I would check an replace the cps

 

Crank position sensor? Cranks but doesn't turn over?

 

He said he already tried the CPS

 

Edited \/ Oleblue explained why I am a DA at times.

 

Revised 11-29-2011

Heres your sign

 

checked my grounds tonight i was impatient.. so they all look decent now.. still same thing wont start and i smell fuel.. almost started.. but didnt. almoststarting to wonder if i have faulty spark plugs but they are new.. bc i spray starter fluid in the intake and still no start

 

and yes i did replace the crankshaft sensor on top of the transfer case.. but ive read there is a camshaft sensor?? to be very honest i didnt know much about mechanics so all these terms sre new but once i find the part ive been able to replace.. am at a standstill though now.. just flipping through the haynes manual and trying to troubleshoot.

and i read through that long text.. it said something about the c101 connector?? on the firewall and its connected to the TCU?? anyone who can explain what those two things are and maybe tell me how to find on the firewall?? im not figuring that part out....

really i appreciate any and all help here guys, thanks.. im just trying to get this done myself.. i recently moved across the country so i DO NOT trust any mechanics out here.. worried ill give to them and replace things ive already done.

 

the camshaft sensor is under the distributor. They can cause no spark also, its just alot more rare for them to go out. Is your issue no spark?

 

.OLE blue.. so i did pull a spark plug and rested it against the engine and there was spark.. so im not sure should i pull each plug one at a time and check them all?? almost acts as if its flooded out though when it wont start.

 

Tps?