Eagle_SX4 Posted July 23 Share Posted July 23 Had an adventure today when I had 3 failures simultaneously. Was driving today and when the truck sputtered and died. I was doing 60 mph. I thought I had just run out of gas. Luckily I was on my way to my parents house and my mom brought me some gas and after adding about 3 gallons of gas the fuel gauge needle came off of empty but still wouldn't start. It was sputtering but wouldn't stay running. Opened the hood and found that the map senor vacuum on the throttle body had come loose and plugged that back in but it still wouldn't start. Next I texted the CPS and it tested at .35 volts AC. Which according to Cruiser54 is a failed/failing CPS. My question is how often does a CPS fail while driving? I had read about no starts because the CPS is bad but not anything about it failing while driving? Or is it just a coincidence that it failed after the map senor vacuum line popped out? Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted July 23 Author Share Posted July 23 Can confirm that the CPS is dead thanks to the R.E.M. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 23 Share Posted July 23 I had it die on me once. Granted the fly wheel hit it and destroyed it thus it died on me. Was interesting. But flat out failing, no. I thought I had experienced such on Chunk but that was the coil contacts being dirty which in a sense is similar. Link to comment Share on other sites More sharing options...
JeepSchmidt O'Guinness Posted July 26 Share Posted July 26 Had one fail on my 95 xj at about 45mph on a HW once. Engine just died. It was before I knew what any symptoms / diag procedures were. So not sure if the cps failed or just backed the bolts out. This was back when the cps was still dealer available, and a new cps fixed the no crank condition. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted July 27 Author Share Posted July 27 I replaced the CPS today and it still didn't start. I tested the new CPS with my volt meter and was getting about .53 AC volts. So it tested good. The rem code "CPS Crank Fault" occurs because the computer doesn't see any rpm while cranking. Which in most cases is the CPS but in rare occasions like mine when the distributor is not turning it throws the same code. This is the description of that code from https://nickintimedesign.com/rem-codes-description/ CPS Crank Fault: No Engine RPM Detected after 3 seconds of starter engagement. Possibly faulty CPS, engine cranking speed too low. On a hunch I was watching the SYN readout on the REM and it was not spinning while cranking. About 5 months ago I replaced the cam gear on the distributor because it was being ground down by the cam. I pulled the distributor out and the cam gear I put on has been ground down worse than before and now there is no teeth on the cam gear for the cam shaft to grab. So this means I will need at minimum a distributor gear but that will probably get chewed up as well. An engine rebuild looks to be in my near future with all of that destroyed cam gear going through the oil. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 27 Share Posted July 27 How is the engine eating up the distributor gears? This would have to mean you’d be getting very little oil pressure too until it just stops like how it did on you. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted July 27 Author Share Posted July 27 8 hours ago, eaglescout526 said: How is the engine eating up the distributor gears? This would have to mean you’d be getting very little oil pressure too until it just stops like how it did on you. I don't know the cause of the issue. Based on how much oil is getting into my air filter I know my oil pump is functioning. However I haven't hooked up a mechanical oil pressure gauge to verify that the oil pressure gauge in my cluster is correct. The one in my cluster was showing about 45 psi cold and about 20 psi hot. But to test it I need to get another distributor. Link to comment Share on other sites More sharing options...
ratrapp Posted July 27 Share Posted July 27 is the cam gear chewing up as well?unfortunatly think about where the metal from the gear has went through the engine,twice now. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted July 28 Author Share Posted July 28 I swapped in a newly acquired junkyard distributor just to see if I could get it running and it still won't start. I did properly index it after finding TDC. After not starting I tried rotating the distributor 180 degrees to see if I had TDC on the wrong stroke but it still didn't help so I switched it back to how it was when I indexed it. The rem still shows CPS Crank Fault. I double checked the CPS with my voltmeter and it says I am getting .57 volts AC. And about 215 ohms between the 2 wires on the CPS. I then checked for continuity on the CPS wires to the computer and both wires have 0 resistance between the engine bay plug and the computer plug. I then swapped the computer with a known good computer and the problem is still present. The CPS Crank Fault rem code keeps coming back when cranking. The next step is to order another CPS and see if a different one fixes my issue. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted August 1 Author Share Posted August 1 Got another new CPS installed (NTK) and it still doesn't start. This one reads at .35 volts AC. I ordered 2 so tomorrow I will try the other one. Also checked compression on cylinder #3 it was 125. The sparkplug was wet with gas. Definitely not getting any spark. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted August 1 Author Share Posted August 1 Also if any one was wondering this is what the distributor gear looks like that got chewed up. I pulled it off and turned the old distributor into an oil pump primer. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted August 1 Author Share Posted August 1 I just tried the 3rd new CPS and it still won't start. Measures .54 volts AC while cranking. I really need some help with this. REM still shows CPS Crank fault. I checked the continuity of the wires for the CPS to the computer and they were 0. Ohms so those are good. What else can I check? Link to comment Share on other sites More sharing options...
89 MJ Posted August 2 Share Posted August 2 Could it be something wrong with the ECU? Link to comment Share on other sites More sharing options...
ratrapp Posted August 2 Share Posted August 2 is the cam gear chewed up as well as the dist gear? Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted August 2 Author Share Posted August 2 11 minutes ago, 89 MJ said: Could it be something wrong with the ECU? I don't think the ECU is messed up because I have 2 of them and get the same rem code with both of them. My backup ECU was in my truck when I bought it and pulled it out when I found a 1990 manual transmission ECU in the junkyard. The 1990 ECU ran great until last week. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted August 2 Author Share Posted August 2 7 minutes ago, ratrapp said: is the cam gear chewed up as well as the dist gear? It is chewed a little bit but not enough to stop the new distributor from rotating. The REM has a sync readout with a rotating animation that is now turning but wasn't before I swapped the newly acquired distributor in. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted August 2 Author Share Posted August 2 Here is a very short video of it cranking just to show that the distributor is turning. VID_20250801_183435337~2.mp4 Link to comment Share on other sites More sharing options...
Ωhm Posted August 2 Share Posted August 2 On 7/27/2025 at 10:10 PM, Eagle_SX4 said: I then checked for continuity on the CPS wires to the computer and both wires have 0 resistance between the engine bay plug and the computer plug. You can PASS the continuity test, but each wire should also be tested for Short To Ground (STG). ECU disconnected. Take measurements at CPS connector, also disconnected. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted August 2 Author Share Posted August 2 10 minutes ago, Ωhm said: You can PASS the continuity test, but each wire should also be tested for Short To Ground (STG). I did check that and there is no connection between either wire and ground. And no connection from the CPS wires to ground. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted August 2 Author Share Posted August 2 @NickInTimeFilms do you have any suggestions. Is there any reason other than a faulty CPS that the "CPS Crank fault" error would pop up on the R.E.M.? Link to comment Share on other sites More sharing options...
Ωhm Posted August 2 Share Posted August 2 With both CPS and ECU disconnected, each wire has continuity, each wire is NOT STG, but could each wire be shorted together? Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted August 2 Author Share Posted August 2 33 minutes ago, Ωhm said: With both CPS and ECU disconnected, each wire has continuity, each wire is NOT STG, but could each wire be shorted together? I don't think so I didn't have my wire diagram with me so I just tested all the pins at the computer connector to find which ones were connected to the CPS. Only one pin connected with each wire. C1 and D1. I found my wire diagram and found out the sensor is actually called the Engine Speed Sensor not the Crank Position sensor which I find odd. I will test tomorrow to see if the computer is grounding the white wire when cranking. Does any one know where the ECU ground is at? I can't find mention of it anywhere. Edit: found it on the diagram the ECU is grounded at G105. Where is that? Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted August 2 Author Share Posted August 2 Looks like the ECU shares the ground with the fuel injectors, oxygen sensor and knock sensor. According to Cruiser54's notes it grounds at the engine block near the dipstick. I will clean and refresh that ground and the ground strap that goes to the body up by the wiper motor and maybe I will have a running truck again. Link to comment Share on other sites More sharing options...
Ωhm Posted August 2 Share Posted August 2 88ElectricalManual still calls it a Engine Speed Sensor, but changed the ECU verbiage to ENGINE SPEED INPUT. C201_D1 at ECU is NOT sensor ground as shown in the 87ElectricalManual. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted August 2 Author Share Posted August 2 47 minutes ago, Ωhm said: 88ElectricalManual still calls it a Engine Speed Sensor, but changed the ECU verbiage to ENGINE SPEED INPUT. C201_D1 at ECU is NOT sensor ground as shown in the 87ElectricalManual. To verify if C201_D1 is ground as shown in the 87 diagram it should be connected to either C201_B11 or C201_B12 with the ECU unplugged. I will test that theory tomorrow. Link to comment Share on other sites More sharing options...
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