Is my CPS bad?

I've been trying to hunt down my idle issue that has started getting worse as of a few days ago
(2001 xj)

idles fine when cold but then when it heats up it feels like it wants to die and starts misfiring. I removed the cap for the cam sensor and sprayed out some dirt or rust and put it back and now it finally showed up P1391 (P), prior it wasn't throwing any codes. I'm trying to see if its the cam sensor or the crank sensor. Is the idle becoming shit when it starts heating up a characteristic of one individual one or both? That way I can narrow it down to one specific part instead of hunting all over.

Sorry I know this seems to have been gone over a ton but if I can narrow it down to one then I dont have to spend double the $$

Thanks

O2 sensors working right ? Tested them ? They have a lifespan of about 100-150,000 miles. Tested the Coolant Temperature Sensor and the Intake Air Temperature Sensor ?

P1391 - Intermittent Loss of CMP or CKP Signal. Loss of the Cam Position Sensor or Crank Position sensor signal has occurred.

P1391 – Possible symptoms:

- Check Engine Light ON
- random misfire/stumble/stalling, often over bumps or right turns and when going into reverse.


Possible causes
- Faulty Camshaft Position (CMP) Sensor
- Camshaft Position (CMP) Sensor harness is open or shorted
- Camshaft Position (CMP) Sensor circuit poor electrical connection.

Symptom:

CMP SENSOR OUT OF SYNC
-DAMAGED TONE WHEEL/FLEX PLATE (CRANKSHAFT)
-DAMAGED TONE WHEEL/PULSE RING (CAMSHAFT)
-IRREGULAR LAB SCOPE PATTERN OF CMP SIGNAL

INTERMITTENT CKP SIGNAL LOSS WHEN WIRING IS WIGGLED
-IRREGULAR LAB SCOPE PATTERN OF CKP SIGNAL
-WIRING HARNESS INTERMITTENT

INTERMITTENT CMP SIGNAL LOSS WHEN WIRING IS WIGGLED
-SENSOR CONNECTOR/WIRING
-CAMSHAFT POSITION SENSOR
-CKP SENSOR CONNECTOR/WIRING
-CRANKSHAFT POSITION SENSOR


Potential Fixes:

Fix #1:
Inspect your wire harnesses for damaged wires, chafed insulation, or failed wire splices. 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.

Fix #2:
Timing may off. Re-index the distributor per the FSM instructions, or replace faulty distributor/cam sensor module.

Google Scan Tools, O-Scopes and Toothpicks, and read the article.

A mis-indexed distributor 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 factory procedure must be used as outlined in the service manual.

Tim_MN said:

O2 sensors working right ? Tested them ? They have a lifespan of about 100-150,000 miles. Tested the Coolant Temperature Sensor and the Intake Air Temperature Sensor ?

P1391 - Intermittent Loss of CMP or CKP Signal. Loss of the Cam Position Sensor or Crank Position sensor signal has occurred.

P1391 – Possible symptoms:

- Check Engine Light ON
- random misfire/stumble/stalling, often over bumps or right turns and when going into reverse.


Possible causes
- Faulty Camshaft Position (CMP) Sensor
- Camshaft Position (CMP) Sensor harness is open or shorted
- Camshaft Position (CMP) Sensor circuit poor electrical connection.

Symptom:

CMP SENSOR OUT OF SYNC
-DAMAGED TONE WHEEL/FLEX PLATE (CRANKSHAFT)
-DAMAGED TONE WHEEL/PULSE RING (CAMSHAFT)
-IRREGULAR LAB SCOPE PATTERN OF CMP SIGNAL

INTERMITTENT CKP SIGNAL LOSS WHEN WIRING IS WIGGLED
-IRREGULAR LAB SCOPE PATTERN OF CKP SIGNAL
-WIRING HARNESS INTERMITTENT

INTERMITTENT CMP SIGNAL LOSS WHEN WIRING IS WIGGLED
-SENSOR CONNECTOR/WIRING
-CAMSHAFT POSITION SENSOR
-CKP SENSOR CONNECTOR/WIRING
-CRANKSHAFT POSITION SENSOR


Potential Fixes:

Fix #1:
Inspect your wire harnesses for damaged wires, chafed insulation, or failed wire splices. 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.

Fix #2:
Timing may off. Re-index the distributor per the FSM instructions, or replace faulty distributor/cam sensor module.

Google Scan Tools, O-Scopes and Toothpicks, and read the article.

A mis-indexed distributor 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 factory procedure must be used as outlined in the service manual.

Click to expand...

awesome, thanks. Weird a toothpick of all things, I'll give this a try in the morning. Just redid the ground wires (after this issue came up) so i'll test the coolant and air temp sensor as well, appreciate it.

OP says 2001 XJ, that means DIS. So no distributor to "index"The later models with pre-cats are also known for issues with "heat soak". Wrapping injectors, installing heat wrap under intake mani, and maybe a heat resistant blanket on your exhaust manifolds might help. Usually, vapor lock occurs.. but maybe yours is slightly more tollerant to it?

Pending mileage, may not be a bad idea to replace your crank sensor.

I mis-spoke slighlty, but the Scan Tools, O-Scopes and Toothpicks article explains it all very well for driveway mechanics and for shop technicians.

Updated Fix #2:
Timing may off. Re-index the distributor/cam sensor per the FSM instructions, or replace faulty distributor/cam sensor pickup module.

I reindex the cam sensor, unfortunately now im getting no start now hmmm

Is that magnet supposed to be loose from the sensor? its still contained when the cap is on not thrashing around in there

Edit: it seems after a bit of googling that magnet is not supposed to be loose.... going to go to napa tomorrow and grab one

If the magnet is loose, you need a new cam sensor pickup.

Well, looks like it came loose, oh well new parts are always good and this would explain the not starting. I'm going to get the whole assembly tomorrow.

Couldn't deal with letting it sit there another night so i went out and replaced it in the snow, now it starts and immediately dies unless I give it gas. I'm guessing its just flooded right now from trying to start it a few times unsuccessfully ? Just wanted to get a second opinion before I let it run and hurt something else.

Is it idling rough when hot only after a hot restart, or just whenever it gets warmed up?

After a hot restart = heat soak issue

Heat soak in snow ?

For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM or poor battery charging. Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem.

A faulty Coolant Temperature Sensor may also cause similar symptoms. Testing of the CTS is recommended as part of the diagnostics. A poor ground at the ignition coil can also cause similar symptoms.

The reboot symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal. (3) The ECU will usually relearn the idle settings after a short period of driving and the engine will start and idle normally.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds.

If the symptoms reoccur, you need to have your battery and/or the alternator Load Tested at a repair shop or auto parts store. This is usually a free service they offer to bring in potential customers. Handheld testers are very inaccurate and will usually pass marginal alternators. Even with low battery voltage, the engine will start, but the ECU can re-boot multiple times and a new battery may be required.

Cleaning the Idle Air Controller (IAC), regular tune-ups, and using fuel injector cleaner should be part of your routine preventative maintenance for smooth starts.

So I bought it to the dealership because its my daily and I cant keep throwing parts at it. Theyre saying it needs a valve job, perhaps that is true but I dont see how thats causing the issue of it running fine at idle and misfiring when warm wouldnt that just be constant . Getting pretty pissed that they charge 315$ for diagnosis and cant diagnose shit.

Most Dealerships are useless at diagnostics. They don't make any money spending time on diagnostics, they make money on major repair projects (like valve jobs) and by replacing parts that may or may not need replacing.

If actually necessary, bolt on low mileage head, and your valve job is done.

You were well on your way to diagnosing it and fixing it yourself, you just bailed out too early.

That half moon looks bent--some coffee grinder type isht.

Tim_MN said:

Most Dealerships are useless at diagnostics. They don't make any money spending time on diagnostics, they make money on major repair projects (like valve jobs) and by replacing parts that may or may not need replacing.

If actually necessary, bolt on low mileage head, and your valve job is done.

You were well on your way to diagnosing it and fixing it yourself, you just bailed out too early.

Click to expand...

Agreed, I did bail out early but I needed my car back asap and figured this would be the end all be all fix, lesson learned I suppose. They were indeed pretty useless 600$ and I got a new IAC out of it.... but on that note it runs a little bit better. The kicker is they stole my fuel line disconnect under my passenger side seat, 10$ but still the principle of it.

After getting it back I noticed the #3 injector has a large crack on it and spins freely I'm guessing there's a leak and luckily I already have injectors I was going to put in 0280155917 sitting in the center console, putting them in today and looking forward to seeing what happens.
I'd be surprised if it needed a valve job the head seems to have been replaced with a tupy casting before I bought but I suppose its not out of the question.

gradon said:

That half moon looks bent--some coffee grinder type isht.

Click to expand...

Yeah, if I didn't spend a large amount of time researching issues with that I would have shit myself seeing that lol, but luckily about 10 minutes of time and a whole new assembly it wasn't so bad.