Engine Stops - doesn't start (?for a while?) - JeepForum.com
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post #1 of 9 Old 05-29-2020, 01:03 PM Thread Starter
snyper82
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Engine Stops - doesn't start (?for a while?)

I've been able to make i happen twice but no more.

I get my 4.0 started, it runs (great, I might add) for about 1-2 minutes then stops like it was just simply shut off.
The first time - I charged the battery thinking that was it - with a 1.5a 12v "quick" charger for about 15min. It started back up.
  • during this time I checked the resistance on the crank position sensor - not shorted
  • the battery before and after reads almost 12v; it's like 11.8
  • I doubt that charger did much, it's not a powerful charger; however it may have juiced up something?!? I left the terminals connected.
The second time, I started it, let it run while I put away the charger and wrapped up the extension cord - it died about a full minute after starting it - same thing, like someone just turned it off with the key.

Now when I try to start it, the whole jeep shakes while the starter is engaged - bu the starter sounds nice and strong.


History:
  • This weekend/week I replaced the oil pan gasket (again) because I had to bang it out for the oil pump to fit (Melling HV)
    • This required a removal and re-install of the starter
    • I also had to turn the engine manually to ensure the crank wasn't hitting the oil pump
    • I made sure everything belt driven turned at the same time and I did it very slowly
      • This may be the issue?
  • I also replaced the o-rings on the oil filter housing
  • I stared fine that day (Tue), rev'd fine, nice and smooth, no ticks - we did this twice and it had no issues.
    • Oil pressure is just above 40 on the dash gauge and fluctuates when you rev and let off (i.e.: drops slightly after letting off the pedal)
  • It sat until today - now this issue.


I need to know where to start and go for troubleshooting this


Thanks in advance for your help, I love these forums!


1998 Black XJ - Stock, for now...
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post #2 of 9 Old 05-29-2020, 05:22 PM
Photoweborama
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Cam position sensor. You get to it from the inside of cab. I paid to have mine fixed, but itís not hard to do..


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post #3 of 9 Old 05-29-2020, 05:24 PM
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This one Iím 99.8% sure the CPS is it..


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post #4 of 9 Old 05-29-2020, 05:35 PM Thread Starter
snyper82
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Isn't the cam position sensor in the distributor??

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post #5 of 9 Old 05-29-2020, 07:59 PM
CJ7-Tim
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The first thing to suspect is the last modifications or repairs that were done. Go back over you work checking for loose connections, loose wire plugs, bent or pushed back wire plug pins, and wires that may have been improperly secured and have contacted sharp metal edges or hot engine parts. Look for cut, melted, or chafed wire insulation.

If you are sure there are no issues from any recent work, you could suspect the Crankshaft Position Sensor on the transmission bell housing is going bad. A faulty CPS is the most common cause for random stalling. Testing the CPS is very simple.



CPS/CKP failure is very common. The CPS/CKP can stop working with no warning or symptoms and the engine will not run or the engine may randomly stall for no apparent reason. Typical CPS lifespan is about 150-200,000 miles.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when the engine gets hot, but works again when it cools back down.

Typical CPS Symptoms, (not all symptoms may be present, or occur at the same time) -
- Random stalling
- Starter cranks and cranks but engine won't start up
- Fuel gauge and voltage gauges may not work or display properly.
- You sometimes will have NoBus displayed on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- Fuel pump should run and prime for 3-5 seconds.
- No spark at the spark plugs.

When the ignition key is first turned ON, 12 volts travels from the ignition switch to the ASD relay. The PCM provides ground to the ASD relay to energize it. The ASD relay sends the 12 volts to the primary side of the coil. If after a few seconds no signal is detected from the faulty CPS, the PCM opens the ASD relay and 12 volts power to the coil and fuel pump is removed.


If the CPS/CKP is failed sometimes the OBD-II code reader cannot make a connection to the computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed.

Diagnostic steps to help confirm the CPS is the cause of your no-start:
-You should be able to verify a bad cps, by unplugging it, and turning the ignition key to ON. If the voltage gauge and/or the fuel gauge now displays correctly, replace the CPS.
-Unplugging and reconnecting the CPS sensor where it connect to the main harness near the back of the intake manifold usually resets the ECU and if the jeep fires right up after doing this you can bet that the CPS is faulty and needs to be replaced.
-Exchange the fuel pump relay and the ASD relay with one of the other similar ones in the PDC to eliminate these relays as the cause of the no-start. Confirm that the fuel pump runs for 3-5 seconds when you turn the ignition key to ON.
-Eliminate the NSS as a cause of no start. Wiggle the shift lever at the same time you try to start. Put the transmission in Neutral and do the same. Do the reverse lights come on when the shifter is in Reverse?
-Inspect the wires and wire connectors at the O2 sensors on the exhausts pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will lose communication.
-Check the ground connection for the PCM. Make sure it is clean, snug, and has no corrosion.

If you buy a new CPS, get a genuine Jeep CPS. Most auto parts stores sell cheap crappy Chinese "Lifetime Warranty" parts that are poorly manufactured from inferior materials and are often out of specification, or even failed, right out of the box. The ones that aren’t faulty often have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts. Buy good quality repair parts and genuine Jeep sensors for best results.
You must also perform 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 and replace as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU will behave oddly until you remedy this.
Crankshaft Position Sensor Connector (CPS/CKP)
.

.

CPS Testing
TESTING PROCEDURE 1991 –2001 4.0L H.O. engines
1. Near the rear of fuel rail, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C or 2 and 3 (See Image). Ohmmeter should be set to the 10K-or-2OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

TESTING PROCEDURE for 1987 –1990 4.0 L engines
Test # 1 - Get a volt/ohmmeter 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 the CPS is out of that range by much, replace it.
Test # 2 - You'll need a helper for this one. Set the 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 helper 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.
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post #6 of 9 Old 05-29-2020, 10:26 PM Thread Starter
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Holy crap, I love this reply!!! Awesome stuff.

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post #7 of 9 Old 05-30-2020, 12:55 AM
Photoweborama
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Quote:
Originally Posted by snyper82 View Post
Isn't the cam position sensor in the distributor??

Lol!!


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post #8 of 9 Old 05-30-2020, 12:56 AM
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Yes, thatís it! Itís that sensor!


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post #9 of 9 Old 06-02-2020, 05:31 AM Thread Starter
snyper82
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It was the crank position sensor, located on the bell housing. Not too bad to replace and fired right up!

Thanks guys for all the help!
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