metrictonner Posted August 15, 2013 Share Posted August 15, 2013 It was running fine the last time I parked it but I don't seem to be getting any signal from the computer to the ignition coil module at all. It cranks, turns on the fuel pump and lights up the dash and accessories fine. Any suggestions? Link to comment Share on other sites More sharing options...
Minuit Posted August 15, 2013 Share Posted August 15, 2013 A crank sensor spontaneously failed on me one time with the truck parked overnight. That would be the first place I would check for a no-spark. How long has it been since the engine has been up to operating temperature? Link to comment Share on other sites More sharing options...
metrictonner Posted August 15, 2013 Author Share Posted August 15, 2013 Minuit: I ran it for a few hours a week ago. Between the off and on it got up to temp maybe three times during the day. Thanks. Link to comment Share on other sites More sharing options...
metrictonner Posted August 16, 2013 Author Share Posted August 16, 2013 CPS nogo. You know, that would be hell if my MAT finally went out. That's about the only sensor there is no advertised replacement for. I don't know if it would cause total ignition failure but what are we doing for a replacement MAT nowadays? Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2013 Share Posted August 16, 2013 IAT/MAT will not cause a no spark condition. Link to comment Share on other sites More sharing options...
Zeke&Me Posted August 16, 2013 Share Posted August 16, 2013 Are you getting spark? Check the Ignition control module in the distributor. I find thats the case most of the time. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2013 Share Posted August 16, 2013 Are you getting spark? Check the Ignition control module in the distributor. I find thats the case most of the time. Really? Did you know you can disconnect the harness to that sync generator in the distributor and a REnix Jeep will still run? Link to comment Share on other sites More sharing options...
JeepcoMJ Posted August 16, 2013 Share Posted August 16, 2013 Maybe on your renix it will, but not on any I've ever owned... Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2013 Share Posted August 16, 2013 Maybe on your renix it will, but not on any I've ever owned... Never seen one yet since 1987 that you can't unplug the dizzy harness and it runs fine. The sync generator inside the dizzy has absolutley NO effect on spark. Only sequential firing of the injectors. Try it. I challenge any others on CC to unplug the dizzies on their Renix 4.0s and see if they still run. Please report back. Link to comment Share on other sites More sharing options...
metrictonner Posted August 16, 2013 Author Share Posted August 16, 2013 There is no chance for a spark: The line from the ECU to the coil is dead. As a matter of fact, I sniffed the throttle body inlet and I don't smell any gas either. All of my fusable links have continuity. The closest I've ever come to this problem was when the vacuum hose fell off of the fuel pressure regulator...no such luck now. I agree on the MAT. The Renix manual talks about at least trying to start. The engine electrics seem to be deader than a doornail for some reason. I could say I've replaced everything that was replaceable before this happened but I know that never pulls any weight. Link to comment Share on other sites More sharing options...
Bornindesert Posted August 16, 2013 Share Posted August 16, 2013 The no spark could still be the CPS circuit. Sensor good, connector or wiring bad. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 16, 2013 Share Posted August 16, 2013 Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2013 Share Posted August 16, 2013 TEST the CPS. And, inspect the wiring while you're at it. It could be melted on the exhaust manifold because it was installed without routing the harness properly. Click on the link in my signature and scroll down to about the 8th write-up to see how the harness is supposed to be routed. 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 to 3/8" from the stock 5/16", 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 01-26-2013 Link to comment Share on other sites More sharing options...
metrictonner Posted August 16, 2013 Author Share Posted August 16, 2013 Cruiser: I got .47 VAC and 200 ohms. This is from my OEM CPS. My store-bought one is at 215 ohms. I'm thinking the OEM is ok? Glad to hear that things are probably localized in the CPS. I'm going to check connections and all black grounds off of the ECU and if that is ok I'm going to swap the ECU back to the OEM. So you are the one with those tips? Pretty good, thanks. I've been using the wiring routing clips through 2 or 3 CPS changes already. A tip I discovered is how to install without popping out the plastic bell housing cap. Swing the CPS into position with the lower bolt already finger tightened. I have a 5-speed and when I swapped CPS's back at 130k miles the OEM was clean as a whistle. You are telling me my clutch isn't falling apart, thanks, nice to know. Link to comment Share on other sites More sharing options...
metrictonner Posted August 16, 2013 Author Share Posted August 16, 2013 My part in this topic is officially closed. Thanks for the help. Yaaas the old buggie is now running. No low battery, no open fusible links, no bad grounds, no ignition coil, no CPS, no distributor, no connection shorts, my suddenly dead...had a bad Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2013 Share Posted August 16, 2013 My part in this topic is officially closed. Thanks for the help. Yaaas the old buggie is now running. No low battery, no open fusible links, no bad grounds, no ignition coil, no CPS, no distributor, no connection shorts, my suddenly dead...had a bad Well, what the hell was it? Link to comment Share on other sites More sharing options...
metrictonner Posted August 17, 2013 Author Share Posted August 17, 2013 Ooops. ECU. I think the tipoff was the total absence of coil input from the ECU and no injector squirt. Either the ECU was bad or something else was shutting down the ECU like, as you guys were saying, the CPS. Yet another rebuilt MJ part that didn't last long. The Standard rebuilt ECU lasted about 3 years. The 25 year old OEM is now back in. Think I'll try Cardone next. Why do the swapping? So I know that I always have a tested, working backup ready to pop in when someone says something like...you have a bad CPS. I can go right to my parts bin and pull out a good part to check it out. I also don't have to get hung up on trying to figure out if a new part really works or not. Of course this only works for people who absolutely have to have their Comanche. Link to comment Share on other sites More sharing options...
Warren Mohler Posted August 25, 2019 Share Posted August 25, 2019 I know this is a six year old topic, but after reading I just had to reply before swapping out parts you should always wiggle test unplug connectors check for corrosion. My buddies 88 xj sat in the driveway for five days with a no start condition he was ready to have towed to a shop I just happened to pay a visit that day checked no spark or fuel I unplugged CPS hooked it back up and it fired right up he drove it for two more years before selling with no further repairs. At Jeep training school years ago George Corsones one of the teachers there explained that sealed connectors carrying small voltages can be prone to ozone build up eventually causing open circuit many times just unplug and replug will fix Link to comment Share on other sites More sharing options...
cruiser54 Posted August 26, 2019 Share Posted August 26, 2019 On 8/24/2019 at 5:25 PM, Warren Mohler said: I know this is a six year old topic, but after reading I just had to reply before swapping out parts you should always wiggle test unplug connectors check for corrosion. My buddies 88 xj sat in the driveway for five days with a no start condition he was ready to have towed to a shop I just happened to pay a visit that day checked no spark or fuel I unplugged CPS hooked it back up and it fired right up he drove it for two more years before selling with no further repairs. At Jeep training school years ago George Corsones one of the teachers there explained that sealed connectors carrying small voltages can be prone to ozone build up eventually causing open circuit many times just unplug and replug will fix Always!! Better yet, as a matter of maintenance, do Tips 1 through 5 at www.cruiser54.com Link to comment Share on other sites More sharing options...
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