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!
