JeepFanactic Posted April 20, 2014 Share Posted April 20, 2014 My 1987 MJ 4.0 5spd 85k have been sputtering even after doing a complete tune up. Tested the CPS today and I'm getting .3 on the meter. Will a bad CPS cause the sputtering problems? The jeep cranks up fine. Also on the fuel pressure guage I got 30 psi with the vacuum connected and 38 psi disconnected. Any suggestions will be helpful. Thanks Link to comment Share on other sites More sharing options...
cruiser54 Posted April 20, 2014 Share Posted April 20, 2014 .3 is kinda low. Read this below, and since you have an 87 I would do posts 1 through 5, and really 27, in the link in my signature, before proceeding further. Known issues. 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...
JeepFanactic Posted April 20, 2014 Author Share Posted April 20, 2014 Thanks for the reply Cruiser. I definitely got to get on completing your tips. Do you think I should go ahead and change it anyway? Link to comment Share on other sites More sharing options...
cruiser54 Posted April 20, 2014 Share Posted April 20, 2014 Thanks for the reply Cruiser. I definitely got to get on completing your tips. Do you think I should go ahead and change it anyway? Couldn't hurt as they are a weak point in the system. get a quality one though, and do the drilling mod to it. Also take extra care to route the harness on it properly. Link to comment Share on other sites More sharing options...
JeepFanactic Posted April 20, 2014 Author Share Posted April 20, 2014 Which CPS to get? There are several to choose? High altitude or without. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 20, 2014 Share Posted April 20, 2014 Always get high altitude when given the choice. More timing advance!!! Link to comment Share on other sites More sharing options...
JeepFanactic Posted April 28, 2014 Author Share Posted April 28, 2014 This weekend I did Cruiser's tips 1-4, upgraded the batter cables from kelly works and changed the CPS. The truck idles a whole lot better and has better throttle response but still sputters. I must be missing something. I was looking at the distributer and it has a little play when I turn. The engine doesnt do anything when I move it. don't know if that's normal or not? Link to comment Share on other sites More sharing options...
cruiser54 Posted April 28, 2014 Share Posted April 28, 2014 This weekend I did Cruiser's tips 1-4, upgraded the batter cables from kelly works and changed the CPS. The truck idles a whole lot better and has better throttle response but still sputters. I must be missing something. I was looking at the distributer and it has a little play when I turn. The engine doesnt do anything when I move it. don't know if that's normal or not? Glad to hear of the improvement. Make sure your intake manifold bolts haven't loosened up and that the small tube from the intake to rear of valve cover isn't carboned up. What kind of "play" in the dizzy? Might wanna read Tip # 13 in the meantime. Link to comment Share on other sites More sharing options...
JeepFanactic Posted April 28, 2014 Author Share Posted April 28, 2014 It has a little play when you turn it. But the engine stays the same. This is driving me nuts I really don't want to take it to the shop. I havnt tested any of the other sensors. Are there any other sensors that can make it sputter while driving? Link to comment Share on other sites More sharing options...
airspeed Posted April 28, 2014 Share Posted April 28, 2014 I changed the plugs on my son's 96 XJ and afterwards he complained about the engine "sputtering". His OBDII was reporting a random misfire, don't remember what the code was. Turns out we broke one of the rubber boots on the plug wire and it had a dead miss on number 3 cylinder. I got a spray bottle of water and sprayed it on the plug wires while the engine was running, there it was, bright blue spark. Link to comment Share on other sites More sharing options...
JeepFanactic Posted April 28, 2014 Author Share Posted April 28, 2014 Does anyone know what the oxygen heater relay does? Checked the relays on the passenger side and there is one missing on the far right. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 28, 2014 Share Posted April 28, 2014 Does anyone know what the oxygen heater relay does? Checked the relays on the passenger side and there is one missing on the far right. Heats up the oxygen sensor. Closest relay to the radiator. Did you pull the relays and clean everything up when doing the connector refreshing? Link to comment Share on other sites More sharing options...
JeepFanactic Posted April 28, 2014 Author Share Posted April 28, 2014 I'm actually missing the far left relay. What I found online that's the AC clutch relay? I'll go back and freshen the relays also. Hopefully I can figure out the problem. thanks Link to comment Share on other sites More sharing options...
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