parkia86 Posted July 20, 2013 Share Posted July 20, 2013 I just installed a new CPS this morning because my engine was cranking hard and sometimes wouldn't start. My old cps passed the resistance test but failed the voltage test. It was only putting out .225 VAC. When I ran the same test on the newly installed unit it is out putting .265 VAC. I read on here that the output voltage should be .5. I got the part from NAPA.... Is it possible that the new part is faulty? Anyone know of a better brand? Link to comment Share on other sites More sharing options...
cruiser54 Posted July 21, 2013 Share Posted July 21, 2013 Very possible. Read this: 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...
parkia86 Posted July 21, 2013 Author Share Posted July 21, 2013 Interesting. Not sure how I would drill out the upper mounting hole. Maybe I could adjust the mounting bracket so it sits closer to the fly wheel. Anyways I have NAPAordering another part so I will just exchange it and try again. Has anyone ever done this to their CPS? Link to comment Share on other sites More sharing options...
Geonovast Posted July 21, 2013 Share Posted July 21, 2013 That's what he's talking about, you have to drill out the mounting hole on the CPS in order to get it closer. Without modification, there's zero adjustment to the CPS. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 21, 2013 Share Posted July 21, 2013 Uh, yeah. Drill out the upper mounting hole. Click on the link in my signature so you can view the photos. Link to comment Share on other sites More sharing options...
HOrnbrod Posted July 21, 2013 Share Posted July 21, 2013 Very possible. Read this: 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 Cruiser, as I'm sure you know the HO's use a CPS and the induced ACV works on the same principle and the Renix, just different time slots in the flexplate / flywheel. The only CPS checks I've ever found for the HOs are the resistance checks, which can be misleading. I agree the CPS induced ACV amplitude output would be a much more accurate check, as it is on the Renix. So, have you ever run across any voltage specs for checking the HO CPS ACV output to the ECU? I have not, have searched, and found nothing even in the FSM. Do you figure if measured it would be the same or similar to a healthy Renix ~.5 VAC threshold? Link to comment Share on other sites More sharing options...
cruiser54 Posted July 21, 2013 Share Posted July 21, 2013 No I have not. Would be interesting to test one for AC voltage. Are the HO CPSs 2 or 3 wire? . Link to comment Share on other sites More sharing options...
HOrnbrod Posted July 21, 2013 Share Posted July 21, 2013 They are three wire, .5VDC supply. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 21, 2013 Share Posted July 21, 2013 That's the difference then. Renix is 2 wire AC voltage generating. Link to comment Share on other sites More sharing options...
HOrnbrod Posted July 21, 2013 Share Posted July 21, 2013 Yep. The HO ECU is looking for a pulsed DC signal it looks like. Didn't know the Renix CPU was 2-wire. Perhaps there is a specific test for checking out the HO CPS using the DBR-II test set, but I'm SOL for that. Thanks Pete. :cheers: Link to comment Share on other sites More sharing options...
Geonovast Posted July 21, 2013 Share Posted July 21, 2013 It'd be interesting to hook up an oscilloscope to a few of them(that are running perfectly) and see what we got. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 21, 2013 Share Posted July 21, 2013 It'd be interesting to hook up an oscilloscope to a few of them(that are running perfectly) and see what we got. Do you have the equpment and an HO to do that on? It would be great to have an alternative to the unreliable ohms test for the HOs also. Link to comment Share on other sites More sharing options...
Geonovast Posted July 21, 2013 Share Posted July 21, 2013 I just have my 99 XJ, which should be the same as all HOs, correct? I know the flywheel's the same, but I also know that the connector was changed at least twice. I don't personally own one. The college I attended has quite a few, and may even let me use one, but they're all bench units so it might be interesting, also not USB so no logging on a computer to post it here. I have been trying to find a legitimate reason to talk my boss into buying one for work, but no luck yet. Link to comment Share on other sites More sharing options...
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