1989 Eliminator Posted August 28, 2012 Share Posted August 28, 2012 Okay so I have done a lot of reading into this problem and I am still having a no-start issue. I have replaced the CPS (which is common and its a sensor from the dealer), new plugs, cords, distributor cap, ignition coil. But I am still having the same problem. :doh: I just ordered a ICM and hopefully this could solve it. But just wondering if there was anything else because ive tried everything. The only other thing to replace would be the pick-up coil and the actual distributor... Link to comment Share on other sites More sharing options...
phenryiv1 Posted August 28, 2012 Share Posted August 28, 2012 So it cranks but won't start? i always look to this page for clues, but it seems like you already covered much of it... http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm Link to comment Share on other sites More sharing options...
1989 Eliminator Posted August 28, 2012 Author Share Posted August 28, 2012 it cranks strong and everything. I know I have fuel pressure. It is defiantly a ignition problem I cannot seem to diagnose. I made this post so maybe someone could give me a better idea so I don't waste my money on replacing everything for the ignition system. But thanks for the link. Link to comment Share on other sites More sharing options...
phenryiv1 Posted August 28, 2012 Share Posted August 28, 2012 it cranks strong and everything. I know I have fuel pressure. It is defiantly a ignition problem I cannot seem to diagnose. I made this post so maybe someone could give me a better idea so I don't waste my money on replacing everything for the ignition system. But thanks for the link. I'm with you on not just buying parts without a plan. My start issue has almost always been a dirty/damp CPS connection, but before I took over working on the truck it had a series of no-start issues that I imagine were the CPS but were "fixed" with hundreds of dollars in ignition parts. Link to comment Share on other sites More sharing options...
1989 Eliminator Posted August 28, 2012 Author Share Posted August 28, 2012 I mean its been a few months since I replaced the CPS but I wouldnt guess for it to be dirty again... I suppose I could take it off and see what it looks like but after reading that link its possible for the actual plug for the CPS, that goes into the ICM, could have a bad connection. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 28, 2012 Share Posted August 28, 2012 Test the CPS first. Renix CPS Testing and Adjusting Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark. Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad. The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark. Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected. You should get a reading of .5 AC volts. If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer. Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off. A little trick for increasing the output of your CPS is to drill out the upper mounting hole, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts. Revised 07-30-2012 Link to comment Share on other sites More sharing options...
cruiser54 Posted August 28, 2012 Share Posted August 28, 2012 The sync generator inside the distributor has nothing to do with ignition. Leave it alone. Here's something to try while waiting for your new ICM: 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 Link to comment Share on other sites More sharing options...
1989 Eliminator Posted August 28, 2012 Author Share Posted August 28, 2012 I mean I kind of did all of that already. I replaced the CPS and bought it from the Jeep dealer so its a quality Mopar part. I did all the di-electric grease on all of my connections about a month ago and made sure connections were good. Ill do the CPS/ICM plug once more and give it a better cleaning. Thanks for telling me about the pick-up coil. Time to get cleaning! :wrench: Link to comment Share on other sites More sharing options...
cruiser54 Posted August 28, 2012 Share Posted August 28, 2012 Be sure to check the CPS output. Link to comment Share on other sites More sharing options...
Geonovast Posted August 28, 2012 Share Posted August 28, 2012 How's the ground strap from the back of the block to the firewall? Link to comment Share on other sites More sharing options...
cruiser54 Posted August 28, 2012 Share Posted August 28, 2012 How's the ground strap from the back of the block to the firewall? Actually, have you ever done this? 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 Link to comment Share on other sites More sharing options...
1989 Eliminator Posted August 29, 2012 Author Share Posted August 29, 2012 How's the ground strap from the back of the block to the firewall? The ground strap to the firewall is fine. Ill clean the stud on the engine though. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 29, 2012 Share Posted August 29, 2012 How's the ground strap from the back of the block to the firewall? The ground strap to the firewall is fine. Ill clean the stud on the engine though. If you read the instructions for the ground refreshing, you can see how important that ground at the stud is. Link to comment Share on other sites More sharing options...
1989 Eliminator Posted August 29, 2012 Author Share Posted August 29, 2012 Yeah I read the whole thing and it definatly is important. The possible cause could be because my original rubber valve cover gasket went bad, so i bought a new one but it was a cork one.. cheap and now I see why because there is a "mist" or glaze of oil down the whole side of my engine. Which then got on those ground wires. I'm trying to figure out a way to insulate those from the oil. (I'm going to buy a rubber gasket...$50!). Ill try heat shrink. :thumbsup: Link to comment Share on other sites More sharing options...
sinkrun Posted August 29, 2012 Share Posted August 29, 2012 Mine did this after some work under the hood there was a broken soldered ground wire connection in the main engine wiring harness. I did just what you have hundreds in new sensors several weeks on it. I gave up towed it to a retired USAF mechanic it took him a few hours to find and fix it. Link to comment Share on other sites More sharing options...
1989 Eliminator Posted August 30, 2012 Author Share Posted August 30, 2012 I cleaned all the grounds, added the two "upgraded" wires and I havent had any problems yet... :thumbsup: it happens randomly so hopefully it lasts. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 30, 2012 Share Posted August 30, 2012 Keep us updated please. The ground refreshing/upgrading is NEVER a bad idea. Link to comment Share on other sites More sharing options...
1989 Eliminator Posted August 31, 2012 Author Share Posted August 31, 2012 Will do. and I have a question about the form on the last page... it suggests to take a #4 gauge wire from the firewall to one of the bolts for the heat shield or fuel rail. This is because the stock braided wire is not enough but why can't I just go from the head to the heat shield/fuel rail? That would make more sense than going from the firewall (A more direct connection). Link to comment Share on other sites More sharing options...
cruiser54 Posted August 31, 2012 Share Posted August 31, 2012 Will do. and I have a question about the form on the last page... it suggests to take a #4 gauge wire from the firewall to one of the bolts for the heat shield or fuel rail. This is because the stock braided wire is not enough but why can't I just go from the head to the heat shield/fuel rail? That would make more sense than going from the firewall (A more direct connection). You want to improve the ground from the engine to the chassis, not from the head to the manifold. Those two pieces are bolted together and ground just peachy. Link to comment Share on other sites More sharing options...
1989 Eliminator Posted September 4, 2012 Author Share Posted September 4, 2012 :agree: Okay that makes sense... but in that article it does say to make another wire going from the chassis to the manifold. Still keeping the one going from the head to the chassis.. Link to comment Share on other sites More sharing options...
cruiser54 Posted September 4, 2012 Share Posted September 4, 2012 :agree: Okay that makes sense... but in that article it does say to make another wire going from the chassis to the manifold. Still keeping the one going from the head to the chassis.. That is correct. Link to comment Share on other sites More sharing options...
1989 Eliminator Posted September 7, 2012 Author Share Posted September 7, 2012 Question on the CPS adjustment... the CPS form says to drill out the top mounting hole in the actual CPS and then push down on it while tightening it onto the bell housing. I'm not seeing how making the hole diameter bigger would make the CPS come closer to the flywheel. Link to comment Share on other sites More sharing options...
1989 Eliminator Posted September 7, 2012 Author Share Posted September 7, 2012 Also, sometimes when I first start up my truck its very weak. Usually it cranks then revs up for a sec and goes back to idle (normal). But sometimes it cranks and starts up staying at or lower than 500 rpm. Link to comment Share on other sites More sharing options...
cruiser54 Posted September 7, 2012 Share Posted September 7, 2012 Question on the CPS adjustment... the CPS form says to drill out the top mounting hole in the actual CPS and then push down on it while tightening it onto the bell housing. I'm not seeing how making the hole diameter bigger would make the CPS come closer to the flywheel. I've got a diagram of it but can't post it up. PM me your email address and I'll send it to you. Link to comment Share on other sites More sharing options...
cruiser54 Posted September 7, 2012 Share Posted September 7, 2012 Also, sometimes when I first start up my truck its very weak. Usually it cranks then revs up for a sec and goes back to idle (normal). But sometimes it cranks and starts up staying at or lower than 500 rpm. Ever clean your throttle body and IAC? -------------------------------------------------------------------- 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 Link to comment Share on other sites More sharing options...
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