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  #1  
Old January 9th, 2018, 11:41
coltsandmudilike coltsandmudilike is offline
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Intermittent crank no start w/ new cps, cam sensor

1998 Jeep Cherokee 4.0 4x4 234k

​​​So I got one for y'all. I've thrown a bunch of new parts at this and had it running for a couple weeks and now I'm right back where I started. It started this morning no problem, ran great, but now it won't start. While running it does have a check engine light but my scanner is not compatible.

PO did cap, rotor, plugs and wires around 5k miles ago.

The fuel gauge and voltage gauge do not work right now, but when they do it will fire. Very rarely will it start with them "dead."
Initially I thought it was fuel related so put in a new fuel pump no dice. Tested the pressure at the rail and it's good. Checked all relays and fuses they looked good. Did replace one for the starter relay. New battery terminals and cleaned the grounds. And a brand new battery when I first bought it.

Moved onto the crank sensor still nothing. It was a Mopar too. I cleaned the NSS. Then a new starter. Then a new camshaft position sensor seemed to do the trick. That lasted for a couple weeks now I'm back to square one. Sometimes if I leave the terminals disconnected for a while the gauges work and she fires. I don't have a clue what do you guys think?
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Old January 9th, 2018, 12:09
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lazyxj lazyxj is offline
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Re: Intermittent crank no start w/ new cps, cam sensor

First, find a OBDII code reader and find out what the code indicates.

Many times the dash goes dead from a bad connection in one of the plugs, under the dash.
This one has cause this problem several times for me.
Under the dash, driver's side, up on the left is a large plug (with many wires) with a small bolt passing through it.
Loosen the bolt and work the plug in and out a few times to clean the contacts, then tighten it up, pushing the plug together at the same time.

A dead dash can also be cause by dirty contacts on the rear of the speedometer assembly, this usually does not effect he running or starting of the engine.
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  #3  
Old January 9th, 2018, 12:41
coltsandmudilike coltsandmudilike is offline
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Re: Intermittent crank no start w/ new cps, cam sensor

Quote:
Originally Posted by lazyxj View Post
First, find a OBDII code reader and find out what the code indicates.

Many times the dash goes dead from a bad connection in one of the plugs, under the dash.
This one has cause this problem several times for me.
Under the dash, driver's side, up on the left is a large plug (with many wires) with a small bolt passing through it.
Loosen the bolt and work the plug in and out a few times to clean the contacts, then tighten it up, pushing the plug together at the same time.

A dead dash can also be cause by dirty contacts on the rear of the speedometer assembly, this usually does not effect he running or starting of the engine.
I know, I know a new code reader is a must. Did the plug and still nothing. It's only the fuel and voltage that are out which makes me think a sensor is the culprit.
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Old January 9th, 2018, 15:50
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Tim_MN Tim_MN is offline
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Re: Intermittent crank no start w/ new cps, cam sensor

The Check Engine Light (CEL) trouble codes are key to any diagnostics, buy or borrow a trouble code reader and determine why the CEL is on.


Quote:
Originally Posted by coltsandmudilike View Post
The fuel gauge and voltage gauge do not work right now, but when they do it will fire. Very rarely will it start with them "dead."
These symptoms should make you very strongly suspect the Crankshaft Position Sensor (CPS).


The Crankshaft Position Sensor (CPS) located on the transmission bell housing. Often this part is also referred to as the CranKshaft Position Sensor (CKP). 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.


Symptoms-
- 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.
- No spark at the spark plugs.
- Fuel pump should run and prime for 3-5 seconds.

If the CPS/CKP is failed sometimes the OBD-II trouble 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 may 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 exhaust pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will lose communication.

If you buy a new CPS, get a genuine Jeep CPS, or the premium one from NAPA. Cheap crappy “Lifetime Warranty” parts are often out of specification or even failed right out of the box. They usually also have a shorter service life than better quality parts. Buy good quality repair parts and genuine Jeep sensors for best results.


Crankshaft Position Sensor Connector (CPS/CKP)
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CPS Testing

TESTING PROCEDURE 1991 –2001 4.0L H.O. engines
1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (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 .5 VAC, replace it.

The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector is on the passenger side, near or on top of the Transfer case, not as shown in the diagram below. Simply follow the wire from the sensor to the wire connector.
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Quote:
Originally Posted by bimmerjeeper

I'm starting to realize people on the Jeep forums are highly expert mechanics .....

Last edited by Tim_MN; January 9th, 2018 at 15:53.
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  #5  
Old January 11th, 2018, 06:35
CWolfe CWolfe is offline
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Re: Intermittent crank no start w/ new cps, cam sensor

Awesome information Tim and thank you for sharing. I'm not currently experiencing any CPS sensor issues, but I'm definitely going to file this in my "things to remember" archives
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Old January 13th, 2018, 12:25
JeepNoob JeepNoob is offline
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Re: Intermittent crank no start w/ new cps, cam sensor

Quote:
Originally Posted by coltsandmudilike View Post
I know, I know a new code reader is a must.
Screw that. If you can get it to a parts store, most places (O'Reilly's, Advance, Vato Zone, etc.) will pull codes for free. (In the hopes of selling you some Chinese-ium crap you may or may not need, of course. )The last time I did that, they actually were able to hook the code reader up to a compooter and give me a print-out of all the DTC's instead of having to scribble them all down.
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Old January 13th, 2018, 14:26
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Tim_MN Tim_MN is offline
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Re: Intermittent crank no start w/ new cps, cam sensor

While friendly and sometimes helpful, most auto parts counter people are clueless about Cherokees. An OBD-II trouble code reader is a low cost investment for the toolbox, and especially useful when the engine doesn't run. I have a good one in the toolbox, and a cheapy one that stays in the Cherokee.
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Quote:
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I'm starting to realize people on the Jeep forums are highly expert mechanics .....
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Old January 14th, 2018, 08:28
JeepNoob JeepNoob is offline
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Re: Intermittent crank no start w/ new cps, cam sensor

Quote:
Originally Posted by Tim_MN View Post
While friendly and sometimes helpful, most auto parts counter people are clueless about Cherokees. An OBD-II trouble code reader is a low cost investment for the toolbox, and especially useful when the engine doesn't run. I have a good one in the toolbox, and a cheapy one that stays in the Cherokee.
Oh, I know. I wonder if there's any way to get codes out of the vehicle without having to use a code reader. I know some of the Chrysler stuff from around the early '00's will do it...
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Old January 14th, 2018, 09:11
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Tim_MN Tim_MN is offline
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Re: Intermittent crank no start w/ new cps, cam sensor

My time is worth money. Driving somewhere to do something that is not necessary when do I have, or should have, the correct tools is a pointless waste of time, and gas. YMMV.
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Quote:
Originally Posted by bimmerjeeper

I'm starting to realize people on the Jeep forums are highly expert mechanics .....
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Old January 14th, 2018, 16:33
JeepNoob JeepNoob is offline
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Re: Intermittent crank no start w/ new cps, cam sensor

Quote:
Originally Posted by Tim_MN View Post
My time is worth money. Driving somewhere to do something that is not necessary when do I have, or should have, the correct tools is a pointless waste of time, and gas. YMMV.
I get that. But money is still money. A tool on my current "wish list" is a scan tool, ideally capable of reading codes on OBD I stuff and bi-directional control. Unfortunately those ain't exactly cheap...

In regards to the topic at hand, OP try flipping the key on your rig from off to on 3 times, off-on-off-on-off-on, fairly quickly (like, within 10 seconds.) Apparently, this will cause any codes to be displayed on the digital odometer. I just tried it with my 2000 Dakota and it worked, but it also seems to work on Cherokees and Grand Cherokees with digital odo's from the late '90's and early '00's.
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Old January 14th, 2018, 17:37
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Ivan Ivan is offline
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Re: Intermittent crank no start w/ new cps, cam sensor

Did you check the relays, located in the PCM, under the hood?

I had an issue with the ASD relay on my '98, that was hard to trace. I pulled the relay and parts rattled around inside. I replaced all the relays while I was at it, and I have not had issues since....
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