I had gone up camping at jones creek and wheeled around a little but right before leaving to come home.my cherokee had started to cut out on all power it would drop to zero rpms and then come right back to normal rpms.Now it got to the point where it would die and not start and if i could get it to run only be for a couple mins then die on me again then it wouldnt start up at all for awhile.So i had just gotten towed back home.NO i get no spark at all? any ideas besides a distribitor.
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NO SparK..NEED HELP
- Thread starter erniesXJ
- Start date
- Location
- on the beach in Ocean View, VA
what year is this rig? It's a classic symptom of failing CPS, but testing varies by year.
- Location
- on the beach in Ocean View, VA
C.P.S. (Crankshaft Position Sensor)
(AKA: CKP and / or engine 'Speed Sensor' in some Daimler-Chrysler publications.)
Do Not Confuse this with the CAM Position Sensor located in the "distributor"! Make sure your counterdrone knows which one you are talking about!
See THIS LINK for Cam Position Sensor Information.
This is the BIG Kahuna of problems for people with no start, hard to start & stall out issues! You do NOT want to have this fail far from home, wheelin' alone, tools in the garage and no spare anyhow... heck, even if ya did have the tools, helpers and a spare it's a major pain to fix beside the trail! This thing is kinda like a serpentine belt; ya won't remember to replace it until it breaks! Unlike a serpentine belt, SOMETIMES.... just sometimes, ya can limp on home... maybe. The CPS should be a regular maintanence item for any Jeep owner but the change out interval is more likely related to heat & vibration rather than miles. If anyone knows the actual time interval recommended by the factory on these, please let me know and I'll amend this page.
View of uninstalled Crankshaft Position Sensor.
View of rear of engine showing Crankshaft Position Sensor & harness highlighted in red.
Great photo showing location of CPS on bellhousing.
[SIZE=-2]NOTE: I found this pic on my harddrive and have no clue where it came from. Had cyrillic writing on larger image & probably came from another Jeep site. I do NOT claim credit for this! Please contact for credit or removal.[/SIZE] CPS: You can check it's basic function but be aware that sometimes the darn things can be 'intermittant' but still read 'ok' when measured due to engine heat/temperature. Even so, these tests will show up a borderline CPS more often than not.
Check the connector first
If you've just stalled out with same symptoms... unplug the CPS & plug it back in. If your motor fires back up you might get off easy, but don't count on it lasting forever. I dunno what doing this accomplishes other than cleaning the connector contacts enough to let additional voltage through to the computer. If unplugging & replugging worked then unplug the connector again and clean those contacts off. Then apply some OX-GARD, or other electrical contact cleaner & protectant (dielectric grease).
There is a distinct possibility that you're not getting a signal due to a faulty connector itself as well. Some people have cured their CPS problems by simply cutting the connector out of the harness and SOLDERING the wires together (Use heat shrink or electrical tape around the wire, of course!) Other's have replaced the connector with a newer, waterproof version from an electrical or automotive supply store.
Test#1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the cps and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If it's out of that range by much; replace it. (* - Note: HO engines are measured from the B & C connectors and should have near zero ohms.)
Test#2 - You'll need a friend to help ya with this one.
Set your volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your friend cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.
Desperate last ditch tip to get home or a few more miles from a failing CPS: - Other than the unplug/replug trick... MJR passed on a trick of using a flat bar and a hammer to 'adjust' the CPS by smacking the CPS bracket and forcing a weak CPS just a tad closer to the flywheel. This lets a weak CPS get a stronger pulse and hopefully generate enough voltage to feed a good signal to the computer again. WARNING! - If ya smack it too hard... it'll go in too far and the flywheel will eat the CPS! Start walking.
Either way, if it fails ANY of the tests... you should replace it and save your self some major pain later. If not, at least carry a spare CPS but be aware that it's a royal pain in the ass to change on a cold motor and ya really don't wanna do it at night, on the trail and with a hot motor if ya can help it!
UPDATE:CPS SENSOR HARNESS REPLACMENT TECHNICAL BULLITEN IN PDF FORMAT.
This one is a 'last resort' fix if you've replaced the CPS already & it didn't fix the problem. The issue is a crappy harness which this bulliten addresses through a replacement of the actual CPS harness. (They call it a CKP harness for some idiotic Daimler-Chrysler reason...)
Tech Tip: - To more easily remove & replace the CPS use a floor jack to support your transmission cross member, remove the two bolts & two studs (replace those with bolts if you break one), then lower the transmission cross member by about 1-2 inches. This will give you enough room to get your hands & tools in for the CPS work. (Especially if you have big hands!)
(AKA: CKP and / or engine 'Speed Sensor' in some Daimler-Chrysler publications.)
Do Not Confuse this with the CAM Position Sensor located in the "distributor"! Make sure your counterdrone knows which one you are talking about!
See THIS LINK for Cam Position Sensor Information.
This is the BIG Kahuna of problems for people with no start, hard to start & stall out issues! You do NOT want to have this fail far from home, wheelin' alone, tools in the garage and no spare anyhow... heck, even if ya did have the tools, helpers and a spare it's a major pain to fix beside the trail! This thing is kinda like a serpentine belt; ya won't remember to replace it until it breaks! Unlike a serpentine belt, SOMETIMES.... just sometimes, ya can limp on home... maybe. The CPS should be a regular maintanence item for any Jeep owner but the change out interval is more likely related to heat & vibration rather than miles. If anyone knows the actual time interval recommended by the factory on these, please let me know and I'll amend this page.
View of uninstalled Crankshaft Position Sensor.
View of rear of engine showing Crankshaft Position Sensor & harness highlighted in red.
Great photo showing location of CPS on bellhousing.
[SIZE=-2]NOTE: I found this pic on my harddrive and have no clue where it came from. Had cyrillic writing on larger image & probably came from another Jeep site. I do NOT claim credit for this! Please contact for credit or removal.[/SIZE] CPS: You can check it's basic function but be aware that sometimes the darn things can be 'intermittant' but still read 'ok' when measured due to engine heat/temperature. Even so, these tests will show up a borderline CPS more often than not.
Check the connector first
If you've just stalled out with same symptoms... unplug the CPS & plug it back in. If your motor fires back up you might get off easy, but don't count on it lasting forever. I dunno what doing this accomplishes other than cleaning the connector contacts enough to let additional voltage through to the computer. If unplugging & replugging worked then unplug the connector again and clean those contacts off. Then apply some OX-GARD, or other electrical contact cleaner & protectant (dielectric grease).
There is a distinct possibility that you're not getting a signal due to a faulty connector itself as well. Some people have cured their CPS problems by simply cutting the connector out of the harness and SOLDERING the wires together (Use heat shrink or electrical tape around the wire, of course!) Other's have replaced the connector with a newer, waterproof version from an electrical or automotive supply store.
Test#1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the cps and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If it's out of that range by much; replace it. (* - Note: HO engines are measured from the B & C connectors and should have near zero ohms.)
Test#2 - You'll need a friend to help ya with this one.
Set your volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your friend cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.
Desperate last ditch tip to get home or a few more miles from a failing CPS: - Other than the unplug/replug trick... MJR passed on a trick of using a flat bar and a hammer to 'adjust' the CPS by smacking the CPS bracket and forcing a weak CPS just a tad closer to the flywheel. This lets a weak CPS get a stronger pulse and hopefully generate enough voltage to feed a good signal to the computer again. WARNING! - If ya smack it too hard... it'll go in too far and the flywheel will eat the CPS! Start walking.
Either way, if it fails ANY of the tests... you should replace it and save your self some major pain later. If not, at least carry a spare CPS but be aware that it's a royal pain in the ass to change on a cold motor and ya really don't wanna do it at night, on the trail and with a hot motor if ya can help it!
UPDATE:CPS SENSOR HARNESS REPLACMENT TECHNICAL BULLITEN IN PDF FORMAT.
This one is a 'last resort' fix if you've replaced the CPS already & it didn't fix the problem. The issue is a crappy harness which this bulliten addresses through a replacement of the actual CPS harness. (They call it a CKP harness for some idiotic Daimler-Chrysler reason...)
Tech Tip: - To more easily remove & replace the CPS use a floor jack to support your transmission cross member, remove the two bolts & two studs (replace those with bolts if you break one), then lower the transmission cross member by about 1-2 inches. This will give you enough room to get your hands & tools in for the CPS work. (Especially if you have big hands!)
- Location
- on the beach in Ocean View, VA
'twas a cut-n-paste and I hope I didn't break any rules with it-- I'll post a link to the rest when I'm on the 'puter that's got the good stuff....
