neonzion

Hey,
I was working on exhaust mods and the ol renix was running beautifully. I left it sitting all saturday and then today morning, I tried to start it, and it just kept turning. im getting no spark to dist or even to the coil (i hooked up a spark plug to the coil thru the wire and held it by metal, i hope thats the right way to do it) i cleaned the coil and the connectors, idk how/what cables to measure on the cps or coil for ohms and volts. there are several threads about this but none ever really explain in detail

The Rooster

Did you clean all your grounds? Clean the grounds to bare metal .... Read the link in my sig hope this helps

neonzion

i got .5 volts from cps. can grounds really make the renix run one day and the next day not start

The Rooster

yes it can

neonzion

i cleaned them up, no difference

67 GMC

Especially the oil dipstick grounds. You sure that the CPS is working? I melted my CPS cable against the exhaust manifold. Couldn't figure out the problem until I traced the wires and saw the melt! That engine gets really hot.
Did you mess around with the Neutral/Start switch at all on the trans? Did you check all the fuses to see if anything was blown? It's probably something simple if you can crank the engine but it doesn't have spark.

BTW-I like to take out a sparkplug (like #1 cylinder plug), re-attach it's wire and touch the base to the valve cover ground to see the spark. That way, you are testing the plug and wire together.

The Rooster

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.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp 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. Reattach securely.
　
　
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 12-04-2012

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The Rooster

i ment to post this one....
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

neonzion

i did the icu cleaning and dipstick cleaning. the cps was a strong 4v and it doesnt look ancient either, i didnt really check for melted wires but while in the area, they did seem alright, i will check again tomorrow. what do you mean by trans switch? i havent checked fuses yet. i already tested for spark both at dist and coil using 3 methods. still no spark. im about to have a breakdown lol i cant afford to send much money and i want to send this pos to a junkyard. i have read SEVERAL renix no spark threads all over the web, and no one really helps, some replace the whole ECU and it works. some people replace coil, CPS, dist, rotor, wires, plugs, and like 3 other ignition components and still no help. I just dont want to spend $200 and still no spark

desertrat71

did you ever get it running?

neonzion

nope, its either the coil, coil pickup, or the renix computer (PCM/ECU?) i havent tested voltages on the coil because idk how

keilan

i had the same problem and all i did was unplug my map sensor and plug it back in and it fired right up and hasnt messed up yet

67 GMC

Check fuses always. Sorry, it wouldn't crank if the trans switch was messed up (I thought it was no crank as well as no start). I'm thinking coil if you can't get a spark at all and the engine turns over. Search for a wiring diagram to trace the path.

neonzion

upon further inspection, cps wire appears to be either very dirty and caked with residue, or slightly melted, could this be the problem? i had the stealership install a new o2 sensor for free, i laos cut my exhaust off so open headers, could either one have damaged the wire? also whats the best aftermarket cps?

The Rooster

That could be a problem... Those wires need to be perfect... Also you must have an o2 sensor to have your jeep run correctly