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(Renix) Will the CPS die while driving...

veedubshafer

NAXJA Forum User
Location
Palmerton PA
and make the vehicle quit? Or on these does it still run but won't restart if it fails? I'm not sure but some cars if the CPS (or maybe its the cam sensor) dies it will still run because its only needed to start it up. One of my RENIX XJ's crapped out while driving today and will not start back up. Seems to have fuel pressure and I instantly jumped the ballast resistor after it happened so its not that. I OHM tested the CPS and its at 240 which is towards the top of the scale so i'm thinking thats it.
 
The CPS/CKP crank sensor is the ONLY sensor that will kill the engine. All of the others will cause running problems, but without the signal from the CPS/CKP (it is a signal generator) providing input to the ECU there will be NO SPARK. Without a functioning crank sensor the ECU doesn't know where the engine is in its rotation.

On the Renix the ECU won't fire the coil until the engine has reached 300 RPMs driven by the starter--that is the main reason Renix engines have to be cranked a lot before they will start.

You can test the Renix CPS/CKP crank sensor--use an ohm meter, resistance should be 200 ohms + - 75 ohms, or 125~275 ohms, however the more you are to the outer edges of the values the more likely it is failing, so I would be suspicious of a 240 reading.

Do you have 12 volts to the ICM/coil? The B Latch relay provides that power and if it is failing you won't have spark.
 
Cam Position Sensor, identifies #1 cyl, is use at start-up and the crank position sensor maintains timing while running.

So if it cut out and DOES NOT restart, it might be the Cam sensor. If it cuts out , is hard to start or won't start SOMETIME, it might be the Crank sensor. Complete failure of either will prevent starting.
 
Thanks guys! Oh, and another test was to put the meter on AC and it should test between .5 and .8 volts. Mine only makes .1 and its at 240 ohms.

You might try loosening the mounting bolts and pushing down on the CPS/CKP then re-tightening the bolts to reduce the air gap, that might give you a stronger signal. Of course, by the time you did all that you might as well replace it.
 
Have you tried the disconnect/reconnect "trick"?
 
Cam Position Sensor, identifies #1 cyl, is use at start-up and the crank position sensor maintains timing while running.

So if it cut out and DOES NOT restart, it might be the Cam sensor. If it cuts out , is hard to start or won't start SOMETIME, it might be the Crank sensor. Complete failure of either will prevent starting.
Complete failure of the CKP (located in distributor, aka cam sensor) WILL NOT cause a no start issue, but it WILL run like crap.

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The scan above is for Renix. Failure of the cam sensor in the later Mopar system will indeed cause a no-start condition. It's happened to me twice. You can get around it by unplugging and replugging the sensor with ignition on. It will then start and run.
 
The scan above is for Renix. Failure of the cam sensor in the later Mopar system will indeed cause a no-start condition. It's happened to me twice. You can get around it by unplugging and replugging the sensor with ignition on. It will then start and run.
Did you not notice the first word in the title? I know thats for renix, Im very capable of reading and understanding... Maybe you arent, since this is a RENIX thread and you somehow failed to notice?
I also know that failure will cause a no start in a chrysler system; but as already stated, this thread is not a chrysler systems related thread. It is a RENIX thread..

Sync signal comes from the CMP not CKP. CKP is the crank sensor commonly called CPS on here.
Yeah, I got my figures messed up.
 
There is nothing wrong with including more information in a thread than the OP requested, especially when it may keep people who search from being misled accidentally.
 
There is nothing wrong with including more information in a thread than the OP requested, especially when it may keep people who search from being misled accidentally.

X2 one of these days we can all use search and find what we are looking for! :D
 
Did you not notice the first word in the title? I know thats for renix, Im very capable of reading and understanding... Maybe you arent, since this is a RENIX thread and you somehow failed to notice?
I also know that failure will cause a no start in a chrysler system; but as already stated, this thread is not a chrysler systems related thread. It is a RENIX thread..

wow. try decaf maybe?
 
Joe offers sound advice. Since I don't know the year of your Renix Jeep, I'll throw something out there. It is a Renix, right? 87 to 88 had the C101 connector on the driver side firewall, held together by a bolt in the center. If you have an 87 or 88, remove the bolt on the C101, clean the black tar crap out of it and clean the contacts the best you can with contact cleaner. Your CPS signal runs through that crappy connector. Also you could check out TSB 18-51-88 which covers eliminating the path of the CPS to ECU throught the crappy C101 connector. If you are suspicious of your CPS, check the output voltage. It's measured in AC millivolts. Unplug the connector, probe the connections, have someone crank it over and you should see about 400 MV. Anything much below that and you could have intermittent issues. Is your Jeep manual or auto trans? Manual trans models tended to sling clutch material that has worn off up on to the CPS causing it to send a weak signal. As Joe says "Year, engine, trans info is important to post".
 
Joe offers sound advice. Since I don't know the year of your Renix Jeep, I'll throw something out there. It is a Renix, right? 87 to 88 had the C101 connector on the driver side firewall, held together by a bolt in the center. If you have an 87 or 88, remove the bolt on the C101, clean the black tar crap out of it and clean the contacts the best you can with contact cleaner. Your CPS signal runs through that crappy connector. Also you could check out TSB 18-51-88 which covers eliminating the path of the CPS to ECU throught the crappy C101 connector. If you are suspicious of your CPS, check the output voltage. It's measured in AC millivolts. Unplug the connector, probe the connections, have someone crank it over and you should see about 400 MV. Anything much below that and you could have intermittent issues. Is your Jeep manual or auto trans? Manual trans models tended to sling clutch material that has worn off up on to the CPS causing it to send a weak signal. As Joe says "Year, engine, trans info is important to post".

The thread was a really simple question. Will the vehicle die if the CPS fails or will it fail and you not know it until you shut it off and try to restart. Its been answered. If you read the thread you will see I already tested it.
Anyway, its an '89 Auto 4.0.
 
THIS THREAD IS ABOUT RENIX!:twak:
I realize this, but we do often yell at people to search before posting, so things do sometimes appear in a search. Many people know that a cam sensor failure will cause no start in a Mopar system, but may not know the somewhat non-intuitive way to get home when it happens. If my slightly off topic interjection saves someone the cost of a tow I'll take my dope slap willingly.
 
Geez, sorry I didn't see where you tested the CPS. I glanced at this last night and when I followed up this morning I must have gotten distracted by all the bitching that happened in the meantime. I think I'll quit answering posts in the morning. Give me a dope slap, too. Did you fix the problem? FWIW, the advice I gave for 87 to 88s still stands as sound.
 
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