MJRemi Posted January 25, 2013 Share Posted January 25, 2013 I'm getting ready to do a few things to the '87. I'm about 90% on keeping the OE motor, albeit in a reconditioned state from a reputable engine shop. My AX15 is a '91 and I just attained a '98 bellhousing for the external slave. Since the engine and tranny are going to be apart, I figured I'd install a new CPS. I believe the CPS is specific to year or group of years but does it read off the engine or transmission? While we're at it, has anyone done the CPS relocation or is it not worth the time and money? Link to comment Share on other sites More sharing options...
cruiser54 Posted January 25, 2013 Share Posted January 25, 2013 Good quality CPS for you 87 to 90 Renix. I've done the CPS mod and it's worth it. Cruiser’s Renix CPS Advance Mod The sensor portion of the CPS needs to slide up the perforated bar towards the top of the engine. Mark the perforated bar's top end with paint or marker. Place the CPS in a vice, just not quite clamping the bar, the sensor resting on the vice jaws, with the Top part protruding. Place a bolt that fits tightly into the hole at the Top part of the bar. With a hammer, tap the Top part of the bar and it will slide through the sensor portion of the CPS. Stop when the sensor portion is about 3/8" from the edge of the bolt hole 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...
Minuit Posted January 25, 2013 Share Posted January 25, 2013 The CPS is basically a magnet that reads grooves on the flywheel. What you do for a CPS is I imagine going to be determined by whether or not the flywheel changes. Even then I think you keep the Renix one. Make sure the replacement is a high quality part and not the $13 Beijing Special. I made that mistake once. Link to comment Share on other sites More sharing options...
airspeed Posted January 25, 2013 Share Posted January 25, 2013 I ordered the Standard Motor Products CPS from RockAuto, #PC307. This is a quality part for ~ $37. It is the "high altitude" with 5 degrees advance built into it. If you look close at the photos in RockAuto you can see where the sensor part is shifted on the mounting bar toward the top. Link to comment Share on other sites More sharing options...
MJRemi Posted January 25, 2013 Author Share Posted January 25, 2013 I usually don't cheap out on sensors or vital components so I'll be sure to get a quality CPS. I didn't even know about the modification with the sensor and bracket. I had read about a relocation to the harmonic balancer or something along those lines. Cruiser54's mod. seems much simpler and much, much ($0) less costly. Link to comment Share on other sites More sharing options...
MJRemi Posted January 25, 2013 Author Share Posted January 25, 2013 I ordered the Standard Motor Products CPS from RockAuto, #PC307. This is a quality part for ~ $37. It is the "high altitude" with 5 degrees advance built into it. If you look close at the photos in RockAuto you can see where the sensor part is shifted on the mounting bar toward the top. Would this result in the same benefit as the above modification? I live at sea level. Are there issues with the "high altitude" at sea level? Link to comment Share on other sites More sharing options...
Geonovast Posted January 25, 2013 Share Posted January 25, 2013 At sea level, you're going to want the standard one. I doubt it'll run correctly 5* advanced. Link to comment Share on other sites More sharing options...
Pete M Posted January 25, 2013 Share Posted January 25, 2013 supposedly the high altitude one is supposed to give more power at lower elevations. :dunno: Link to comment Share on other sites More sharing options...
airspeed Posted January 25, 2013 Share Posted January 25, 2013 These ignition systems are designed with some very specific parameters, they don't need the extra advance at low altitudes. On a stock setup I doubt you would gain anything... Unknown to me my engine had the standard CPS in it, when I changed to the high altitude CPS I did notice a difference. Going over Berthoud Pass at 11,306 ft. I don't need second gear quite as much. Link to comment Share on other sites More sharing options...
Eagle Posted January 25, 2013 Share Posted January 25, 2013 I've been running a high altitude CPS in the '88 Cherokee for years. My house is at elevation 460 above sea level. You don't even notice it's there, and if you drive with a lead foot you won't see any benefit from it. It allows the distributor more advance, but the Renix system also has a knock sensor, so any time you put your foot into it far enough to cause detonation, the knock sensor retards the timing back to where it would be with the seal level CPS anyway. I drive with a light foot, and I figure the high-altitude CPS is probably giving me a couple of miles per gallon. Link to comment Share on other sites More sharing options...
cruiser54 Posted January 26, 2013 Share Posted January 26, 2013 We have knock sensors guys. Use the high altitude sensor if you can find a good quality one still available. Mopar discontinued them. I would use a new one rather than modify one given the choice. Link to comment Share on other sites More sharing options...
airspeed Posted January 27, 2013 Share Posted January 27, 2013 I found mine at Rock Auto ~$35, Standard Motor Products #PC307, made in the USA. It looks and feels like a quality part. Nice over-molded sensor and wire cover. I can't see the inner workings of the actual Hall Effect Sensor but there's not much to a magnet and diode. You can see the five degree shift in the sensor a mounting bracket. Link to comment Share on other sites More sharing options...
Minuit Posted January 27, 2013 Share Posted January 27, 2013 Another victory for Rockauto. Very surprised they're still available. Link to comment Share on other sites More sharing options...
cruiser54 Posted January 27, 2013 Share Posted January 27, 2013 I looked at my Mopar high altitude CPSs today and noticed they were made by Siemens in France. I drilled out the upper mounting hole in the CPS so I could get it closer to the flexplate. Link to comment Share on other sites More sharing options...
airspeed Posted January 27, 2013 Share Posted January 27, 2013 I just went out and looked closer at the one in the photo. Molded in the back of sensor body "Siemens, made in France. It came in a Standard Motor Products box labeled Made in USA? Who knows... Link to comment Share on other sites More sharing options...
cruiser54 Posted January 27, 2013 Share Posted January 27, 2013 I just went out and looked closer at the one in the photo. Molded in the back of sensor body "Siemens, made in France. It came in a Standard Motor Products box labeled Made in USA? Who knows... Weird. Looks just like the Mopar. Link to comment Share on other sites More sharing options...
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