Please. Someone smarter than me help me out! Got a 90XJ that I been trying to get started for couple months. Jeep turns over good and fires but wont stay running. Have 38psi at fuel rail, and have spark at plugs..(although to me it looks weak) but spark nonetheless. So here is what I think is an important hint.....when I take off the coil wire and crank the motor for 10-20 seconds, then place coil wire back on and crank again, it fires right up and will run for maybe 10 seconds then shuts right down. It appears that cranking the motor for a period of time without spark is allowing enough fuel in cylinders so that engine will run for a few seconds, and that it's not getting enough fuel to maintain running condition. Sound right? But I have plenty of fuel pressure. Could it be weak coil or ignition control modual which the coil sits on....not providing enough spark? Also...plugs are all carboned up with black like soot. Is that a sign of poor spark? Hope someone has some ideas here. Thanks

 

If you had a meter, (digital), I'd go ahead and toss three minutes at the AC voltage test for a CPS in my signature for a start. Supper easy, you just unplug it, and probe for .4 or more AC-V while its cranking. Without a hartbeat the patient might not do well....

 

Thanks. I will try that. I did replace the cps already...pain in the ***....but its possible its not putting out enough.

 

If it fires but won't stay running, in addition to what DFlintstone mentioned, for giggles you might try bypassing the fuel pump resistor mounted on the firewall. It's bypassed in "start", but might be strangling power to your fuel pump in "run" when it's back inline.

 

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

 

Thanks for the response. I did bypass the resistor and clean clean up those contacts on icu...however I did not use elec spray cleaner or grease. They didn't look too bad.But will go over it again and see what happens. Anyway to test the icu?

 

There is a test for the ICU but I don't have it. Sounds like you did a good enough job on the connections.

 

Those relays on the passenger inner fender? Juggle them down one way or another if you know what I mean so they're all in a different socket.

This is never a bad idea on a Renix Jeep.

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

 

Yea I think I covered the icu pretty good. I also cleaned up the grounds and wiggled and switched relays around. What confuses me is how the jeep runs and sounds awesome when I --disconnect coil wire and crank it for awhile, then reconnect coil wire. It fires right up, and like I said runs great until what seems like it running out of the fuel cranked into the cylinders. It seems like its not getting sufficient fuel...but got plenty of fuel pressure. I even pulled the injectors back and cranked motor verifying that they were injecting. Just wonder if I have enough fuel but poor spark to ignite it consistantly, unless there is excessive fuel vapor in cylinders. Follow me?? Coil is new.

 

With it running, wiggle the harness along the intake manifold and back to the firewall.

 

OK I'll give it a try and see what happens. I'll have to wait till I get some help though. Check back to my post here later if you would. You been a big help and i thank you.

 

I'm subscribed. There are some other preventative/maintenance/known issue procedures for your Renix if you want to do them.

 

for sure

 

I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals making sure they haven’t retracted into the plastic holder, and then plugging it back together. There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one. Also be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.
ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then plug them back in. I do this on every Renix Jeep I purchase or work on for someone else.
Revised 07/23/2012


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The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

"Gently" wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled




Cruiser’s Renix Sensor Ground Test
　
This sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate.
Set your meter to measure Ohms. Be sure the key is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.
You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.
Revised 06/12/2012

 

OK here's another twist to the puzzle: As I said before, the only time jeep will run for as much as 7-10 seconds is when I pull the coil wire and crank it, allowing fuel vapor build up in cylinders. Then I replace the wire and jeep starts right up and runs till fuel is burnt up...thats what I think is going on. So what I tried to do was give it the gas during that 7-10 sec run time and every time I do it immediately shuts off. As soon as I touch the accelerator it shuts right down. Why wouldn't it continue to burn up vapor in cylinder??? What would make it shut down like that...like you turned the key right off??