squeaky3

ok so i bought an 87 xj a few weeks ago, bought it not running and figured i could get it running

well cranks over fine but no spark, have plenty of fuel air and combustion but no spark out of the coil

the previous owner had replaced the following
crank sensor
ign control module
coil
dist/cap/wire/plugs
spare pcm

ok now i got it running somehow for one day, cleaned some connectors and such up and it ran like crap from not running in while but i got it smoothed out, went out the next day and nothing and still dont have anything

according to the wiring diagram i found online i have power where i am supposed to, crank sensor reads .5 ac volt, cam/sync sensor is good

when i had it running i swapped the pcm with the other one and it had no spark then, swap it back and it ran again so i know that the one pcm is bad, and that the other one at least worked at some point

sorry for the long post but im just not sure where i am missing here, this thing has me stumped

DFlintstone

You probably want to do this weather it's your problem today or not!

Written by Cruiser54 ;


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, and the ECU travel the path through the C101.
The C101 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. Apply a true dielectric grease, not the stuff that came with your brake pads, to the connection and bolt it back together.
　
　
Revised 11-29-2011

cruiser54

Yep. Do the C101 for sure. Here's something else every REnix owner needs to do:

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

squeaky3

thanks guys, i did find that nasty tar crap in the one connector and cleaned it out pretty good

i will go through and fix and upgrade all the grounds i can find and see if that helps

DFlintstone

Hey there. Sounds like you are doing everything right. I'm learning myself. Thought I'd show you this. I guess that connection through the c101 was so bad and so important that they had a process to bypass the c101 for the cps.
(you have an ECM btw, Poewrtrain Control Module's came later)

http://www.bc4x4.com/faqs/yj.cfm?cat=5&faqid=164

cruiser54

FWIW, the bulletin for the CPS bypass included 89s and 90s without the C101, too. But, the C101 was still a major problem. Do not shortcut that refreshing for sure.

I cannot emphasize enough the need for the ground refreshing. A little time and less than $20 and you know it's done. No shortcuts there either. Do it all and don't assume anything. Get your hands dirty.

squeaky3

im not afraid to get my hands dirty, i do work on cars for a living but not real good with the older stuff since my training was on new vehicles and thats all i really work on

but i got some good welding wire and ends and gonna use that for all new grounds and such after the garage warms up

ill see if i cant clean up that connector some more while im at it too and do a lil wiring for the crank sensor, even though i have .5ac volts like i read i should it cant hurt to do it anyways

cruiser54

Tweak the female connectors in the C101 while you're in there.

squeaky3

well i added a whole new ground from the block to the battery with some #2 welding wire and ends, then added a wire from the body to the battery next to the battery with some lil smaller wire, then cleaned up the ground strap

cleaned some more tar out of the big connector

STILL NO SPARK!!!

im not really sure what else is wrong...im gonna check, recheck and recheck all the power and ground wires for everything

this thing is kicking my a$$

DFlintstone

On my mom's Jeep I painted the CPS connector white, so when it wouldn't start she could point at it. "my son says to try un-plugging and re plugging that there"

https://www.cherokeeforum.com/f51/he...ix-links-1397/

Did you separate the coil and icm? I guess those connections can get pretty grody.

Well, I looked all over. Found coil primary resistance figures from zero or 1/2 an ohm all the way to 1.1-1.2, then 1.5 hot....of course open to ground, 12,000-77,000 secondary-93,000 hot. Solved Rubic's cube, but the resistance for an 88 Cherokee coil defeats me. (my 90 fsm neatly leaves that one out, has 2.5 and 4.2, but no 4.0)

squeaky3

yes i did remove the coil from the icm

both of them are new, i checked the resistance of the middle terminal and the output and then the 2 other posts and i know they read something but i dont remember what as it was a few days ago i checked it

cruiser54

Re-check the CPS output.

If it's good, I wold suspect an issue between the CPS and ECU. If that's the case, you might have to check the CPS output on the firewall side of the C101. I have bypassed the C101 by soldering the CPS wires around it. Real easy. I haven't done a write-up on it yet.

squeaky3

its been a few days but i did check for the output at the ecu connector, i will have to recheck that again today

cruiser54

You checked CPS output at the ECU up under the dash?

squeaky3

yes, the ecu is no long bolted up under the dash as the guy i got it from had swaped them out and never bolted it back up under there so its just kinda there now