Need help 98 4.0 cps - JeepForum.com
 
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post #1 of 5 Old 08-01-2020, 06:50 PM Thread Starter
AL5280
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Need help 98 4.0 cps

So recently bought a 98 4.0 manual. Engine was completely rebuilt (have papers) 11k ago. Test drive fine, 50 mile trip home fine, 20 miles to work no problem. On the way home started misfiring badly, got it off the road and towed home. Had code P1319 for crank sensor. Replaced sensor today with correct Mopar OEM sensor. Will start and idles great, however giving it gas won’t get over about 1100-1200 rpm and hiccups if you keep it there. All plugs and wiring looks good. Cap and rotor look good. I am at a loss were to look next.

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post #2 of 5 Old 08-02-2020, 07:21 AM
CJ7-Tim
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Follow the diagnostic suggestions provided by the on-board OBD-II self-diagnostics. It is logical to suspect the most recent repairs or modifications when new symptoms pop up. Yanking all the wire harness around during the engine work may have damaged one or more wires or wire plugs. An improperly secured wire harness may have been damaged by sharp metal or hot exhaust. Visually inspect the related wiring harness and connectors. Check for damaged wires, failed wire splices, and chafed or melted wire insulation. Also look for broken, bent, pushed out, or corroded wire connector pins. Use a volts/ohms multi-meter to check the resistance of the ground wire circuits from each sensor. Replace corroded ground wires/connectors and clean ground wire connection points.


The timing may off. Re-index the distributor/cam sensor per the FSM instructions, or replace faulty distributor/cam sensor pickup module.
Read this article: Scan Tools, O-Scopes and Toothpicks here >> http://jeep.blackonyx.net/pdfs/jcss.pdf
Read this thread >> https://www.jeepforum.com/forum/f19/...e-fix-3487474/

A improperly indexed distributor/cam sensor may exhibit surging, light bucking or intermittent engine misfiring. This will most likely occur when the vehicle is at operating temperature and under a light load at approximately 2,000 rpm. The proper indexing procedure must be used as outlined in the service manual.




P1391 JEEP - CMP or CKP Signal Intermittent Condition

P1391 JEEP Possible Causes

Faulty Crankshaft Position Sensor (CKP)
Crankshaft Position Sensor (CKP) harness is open or shorted
Crankshaft Position Sensor (CKP) circuit poor electrical connection
Loose, cracked, or damaged flexplate
Cam Sensor synchronization out of tolerance
Faulty Camshaft Position (CMP) Sensor
Camshaft Position (CMP) Sensor harness is open or shorted
Camshaft Position (CMP) Sensor circuit poor electrical connection.
Loose or damaged (CMP) pulse ring

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post #3 of 5 Old 08-02-2020, 11:33 AM
jtec
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As CJ7tim added above - P1391-INTERMITTENT LOSS OF CMP OR CKP


the lower RPM misfiring issue has me thinking CMP.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 5 Old 08-03-2020, 08:32 PM Thread Starter
AL5280
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Solved. Turned out to be cam sensor. Bought a new distributor, since cost for it along with new cap and rotor was about $15 more than just a sensor. Set tdc and installed. Fired right up, runs how she should. Bonus have a new CPS and a spare now. Thanks for the help.
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post #5 of 5 Old 08-04-2020, 08:09 AM
jtec
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GREAT !! now its fishing time...

Keep that old DIST if you can - put on a shelf for the future.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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