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 and some fine sandpaper.
Squeeze the springy contacts closer together with some needle nose pliers. Apply some OxGard to the contacts. 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.
I feel this procedure should be performed at least once in the lifetime of a Renix Jeep.
5-11-16
Is the coil on the renix different than the non- renix?
Completely different animals.
Thank you for your quick reply.
Would this cause it to idle low and possibly die at stop signs once the engine has reached operating temperature? It’s a 1990 xj.
Not likely. But it never hurts to be proactive and do the Tips that could contribute to the problem.
Is it possible to put a 91-95 engine bay wiring harness on the 87-90 fuse box? I know that all the sensors are different i just want to make sure the wires will on the bulkhead
Ryan, I don’t know if that’s possible.
The bulkhead is the same shape but pinned differently. Much easier to replace the dash harness, splice late model connectors to the body harness and have everything 91-95 forward from there. My 86 is done this way and I’m working on swapping an 89 as well. Makes for a factory appearance short of a few new holes and some which will need to be capped in the engine bay.
I know this comment is as old as the 4.0 swap in my 86, but while I’m here going through an all original 89, I thought I might add to the knowledge base. Thanks for maintaining these pages.
hello cruiser54… i have real enigma regardind spark.. initially i .pulled the coil wire…. to turn over engine during oil change;;; to fill oil filter. dumb…. probably cranked too many times as i flooded it … however .. no spark now..would the ecu have shut down the asd relay … is there even an asd relay on an 87 rennix?… could a 02 sensor smelling raw gas cause ecu to stop pulse. put in.new plugs… they were wet,,new coil..cleaned the coil leads and checked power there with key on…12,5 or so… also checked power to distributor end of coil wire also 12,5 or so…. but no pulse when cranking… cranks hard. checked continuity on crank sensor… seems good..cleaned grounds..cleaned harness on firewall…tried computer reset but maybe didnt reset…. disconnected battery positive…held to ground 30 seconds..reconnected..turned on key swicth..turned on headlights..turned off switch….nothing.. she was running strong before i pulled coil wire… it had to have messed up the logic… i have not unplugged cpu yet. ive heard on the early rennix the asd relay is in the pcm? where is that? there are only 4 relays by the battery. any ideas helpful… fuel pressure seems good,,
fuel pump comes on and primes with turn of key… if there was an asd relay… would it even allow for 12.5 at the coil and power to fuel pump if defective…. no pulse! bad cpu all of the sudden? reset? maybe a short in harness but too coincidental when pulled coil wire…..
yup ….cps shows 205 resistance and ,5 volts when cranking….guess its cpu time….
No need to do that with an oil change. If you ever want to crank the engine over without spark, just disconnect the CPS plug.
Good Afternoon Cruiser, apreciate all you have done to help us out. I am chasing down an intermittent no start, and stalling issue on an 87 grand Cherokee. I checked and voltage to the fuel pump was around 6 volts it would start and die, I put full voltage to the pump and it would stay running. It had a new pump about 15 years ago, and relly isn’t driven much. It only has 90k miles on it.
My dad took it into a shop and they replaced the crank sensor a few mo the back and it has been fine. I noticed someone put in a new coil. And it is kind of loose on the module. I am wondering if the coil being loose is causing an Intermittent spark loss.
He said it always starts up and dies , and when it stalls when driving it will start and die.
Looking for suggestions
I’ll try your coil connector repair today and see
Check out the coil/ICM connectivity and looseness.
You can bypass the fuel pump ballast resistor on the driver’s side inner fender to give your fuel pump full voltage.
I didn’t see a resistor on the drivers in deer fender, but there was one on the drivers side firewall. It had 2 wires on one side, orange with black tracer. On the other side one wire with orange and black tracer.
Everything on this one seems unique. You really have been a life saver. When I was look8ng at it tonight I noticed a blue vacuum line with a check valve on it that was unhooked just past the check valve. I am slowly working through all your updates. Every one has made it better for sure .
In 1987 there was a bulletin to put the resistor on to quiet the pump down. Someone coulda installed it on the firewall.
The deal you describe as the vacuum line with a check valve is the exhaust for the front axle disconnect. No worries.
also checked for pulse coming from cpu at icm connector…..cranking away…. checked using test light. no pulse. will check sync pulse coil pickup in rotor next with analog meter while cranking
forget everything about an asd relay….. guess those came later. checked sync pulse coil pickup with analog voltmeter while cranking. also no problems. Here is the part i forgot ..we had cut out the rust under passenger rear and welded new plate 2 days earlier. didnt think this was an issue cause she ran fine for 2 days after. had disconnected negative battery but guess that wasn’t enough. pulling coil wire to pump oil into filter….must have aggravated the problem in the cpu after initial power shock from welding. hope i can find a good 89 or 90 cpu for a manual.
I’m doing my ground refreshing / contact cleaning and already have eliminated the C101 connector. On my coil there is a spade terminal above the two coil pins that had no wire attached. What is this for?
Another car somewhere in the world that used the Renix system.
Came here looking for this exact answer. Got my first xj about 8 months ago and you’ve been walking me through this every step. Thank you
Hey cruiser54 I’m sure you’ve heard this a lot but I did an engine swap in my Wrangler from a 4.2 to an 89 renix 4.0 I have no spark and everything is new… I checked all my power and ground wires at the ecu but I’m still not getting spark but it is cranking and getting fuel what should I do?
What are you using for a flywheel/flexplate?
I’m having an issue where I’m driving, first and second gear usually work good, it will go into 3rd but sometimes shifts down, the idle drops then I get stuck on a certain speed, sometimes it will kick in and drives normal, it does it between 35 to 55mph, it just fluctuates between those. I’m going to do the steps, the iac and tps have been replaces, I’m starting to think it’s maybe the shift solenoids or just a bad tranny, no grinding or smell on tranny, when it shifts it shifts good and strong, the overdrive is lacking.
Trans solenoids can be tested for resistance from the engine bay. The instructions should be easily found online. Before doing that, do Tip 10. That’s the connectors you would use to test the solenoids anyway. They can have corrosion and cause issues like you are describing.
Did you ever resolve this? I thought I was the only one mad enough to make this swap, but I wanted an AW4 and had the Renix engine.
Replaced the flex plate on a 89 cherokee. After assembly I drove the truck 3/4 mile and it seemed okay.
One day later: at first it idled very good but it would misfire just above idle. 6 hrs later it misfires at idle and higher. Previous to this I have refreshed the grounds using #4 and #6 cable.
Cruiser i need help.
My jeep is a 1989 cherokee 4.0 renix. 190k
Bone bone stock. Older man owned it and i bought it after him. He had never done anything on your lost of upgrades to do. I just got the jeep not long ago and getting used to it. It ran like total dog shhh. After replacing almost every censor on the jeep….. it runs decent. However… I’m getting backfires through exhaust and intake when putting the engine under a load. Ie trying to floor it or rev it up. New fuel pump intake exhaust manifold gasket. Plugs wires distributor you name it. I’m almost in tears because I’m running out od money and this was supposed to be a fun project for off roading. I’ve had the timing checked and adjusted to make sure that wasnt the issue. Unplugged the knock censor to make sure it wasnt retarding the engine. The backfiring seems to switch sides as it warms up. When its cold it wants to backfire through the intake. When it warms up it backfires out the exhaust. The jeep still drives. Motor feels good but when you put it under a load it acts up. Not sure where to go.
There are so many crappy replacement fuel pumps out there now. Have you tested fuel pressure?
Great tips, done almost all of it. Still having issuess. Any chance u got email for more detailes plz? 🙂
cruiser54private@gmail.com
Do you know what the timing signal voltage is coming from the ecm to the icm. Yellow wire on an 89xj. Have done all of the tips twice still have no spark. And it seems to not have any voltage going out to the icm. CPS has .45v ac.
I don’t know that.
Ok looking at the comments above I’m not sure if ill get an answer. On my 1987 4.0 I’m not getting any spark. I’m getting .50ac from the CPS to the ECU. I believe I’m not getting any signal out of the ECU to the coil. What is a good way to test that? I’ve read test light but I’m not sure if that’s right. And what does the ECU need to see to send spark?
Thank you.
I’ve never found a good test for the ICM, ignition control module. Have you ever cleaned it up inside per tip 3?
Hello, I have a 88 Jeep xj 4.0. My problem is after warming up my Jeep backfires like crazy through the throttle body. I have a new crankshaft position sensor, throttle position sensor, ignition air control valve, fuel pump, check all the plugs all clean and a few months old, new plug wires, no wear on distributor contacts or rotor, new o2 sensor. I’m honestly out of ideas and would appreciate any help.
could be a weak fuel pump. Easy to test pressure with a gauge borrowed from an auto parts store. Which Tips have you completed so far?
I have just done the c 101 cleaning. Also I have fuel pressure. I’m still stumped. Thanks for the help
How much fuel pressure?
I have a 88 Cherokee 4.0 Renix. The ignition coil is excited but not sending the spark to the distributor. Any suggestions ? Thanks in advance!!
I’ve never seen a reliable method of testing those. I think it’s a good idea to have a spare from the junkyard. they rarely fail.
Did you clean the internal contacts yet?