Duncan Moody Posted March 7 Share Posted March 7 I am hoping to get guidance on next steps to solve my crank, no start problem. I am still optimistic it's something simple that I have missed, not done, or not done right, but I don't know what that is. With help from this group and Mostly Renix on FB, I have ruled out a lot, especially related to the sensor itself, and the signal it produces. Here's what I have, what I have tried, and some data. Any tips or direction will be greatly appreciated, including if you know of a knowledgeable person or shop in the SF Bay Area who can help directly. Thanks. 1989 Comanche Pioneer, 4L, 4x4, Automatic Transmission. (No C101 connector). REM II says CPS Crank Fault. Since it won't run, I am not sure what other useful data REM II can provide. Finally got a CPS installed and positioned to get .695VAC at the sensor connector, and .678VAC backprobing at the ECU connector. Swapped 89 ECU with 88 ECU. Still no change. Ran homerun from CPS to ECU. Did the applicable Cruiser54 tips; 1, 3, 4, 5, 7, 8, 9, 29. New Starter relay and switch. (That solved a temporary no crank condition. I could jump the starter to start it then). New ICM. Ran smoothly and strong before it quit, and also whenever I could get it to start and run. Went through several CPS's; some worked for a while (days/weeks), others not at all. Battery at 12.6V min. Discharged/cleared electrical between tests. (touched black and red when off battery). Attempted to take oscilloscope readings on CPS signal, but was unable to get good readings. I assume I did not have it set up right. Problems started ~6 months after a rebuilt motor was installed a year ago, but not sure how that would contribute. New CPS and new Flexplate (Pioneer FRA333) then, but it ran fine for months before the CPS issues began. Intermittent at first, and temporarily fixed too. Link to comment Share on other sites More sharing options...
acfortier Posted March 7 Share Posted March 7 So your coil isn't getting a signal when you crank? I had a really weird situation where the input to the coil was extremely loose and would cause intermittent crank, no start conditions. I could push/pull on the plug and it would cut out and die. I guess I would check voltage at the coil and check the terminals on that plug? Link to comment Share on other sites More sharing options...
Ωhm Posted March 7 Share Posted March 7 Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage_(B+) on the following pins (use battery_negative terminal for ground): D1_5: B+ (Hot at all times) D1_6: At KEY ON only (B+ (Hot for 2-3 seconds)). During CRANK Hot at all times. D2_4: B+ (Hot during KEY ON and Hot during CRANK). Link to comment Share on other sites More sharing options...
Duncan Moody Posted March 8 Author Share Posted March 8 Ohm: Thanks. Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage_(B+) on the following pins (use battery_negative terminal for ground): D1_5: B+ (Hot at all times) Yes, 12.4V (Same as battery) D1_6: At KEY ON only (B+ (Hot for 2-3 seconds)). Yes, 12.4. During CRANK Hot at all times. Yes, 11V during crank D2_4: B+ (Hot during KEY ON and Hot during CRANK). Yes, 12.0V on, and 11V during crank acfortier: Thanks. The 2 connectors on the ICM base are tight, no signs of corrosion. I'll try to test it tomorrow. Link to comment Share on other sites More sharing options...
Duncan Moody Posted March 11 Author Share Posted March 11 OHM: I saw on another post that you mentioned that if the CPS is too close to the flexplate it confuses it. I have been trying to get it as close as possible without touching, like .010" to get higher voltage signal. Too close? I assume it's hard to quantify a clearance distance due to the variation between sensors. Link to comment Share on other sites More sharing options...
Ωhm Posted March 11 Share Posted March 11 My understanding is that CPS AC voltage lives within a 4.1vdc world. This allows the AC signal to connect to the Analog-to-Digital (A-to-D) converter. The converter output creates a square wave which then can be read and counted by the ECU as ones and zeros. My point was I’m sure there are both upper and lower voltage limits for the position of the CPS. On 3/7/2024 at 6:23 PM, Duncan Moody said: Finally got a CPS installed and positioned to get .695VAC at the sensor connector, and .678VAC backprobing at the ECU connector. This is the highest CPS VAC reading I’ve seen on this site. It made me wonder when I first saw this. Link to comment Share on other sites More sharing options...
cruiser54 Posted March 12 Share Posted March 12 I've seen one that high. Link to comment Share on other sites More sharing options...
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