01 stock xj. No problems besides this one. Replaced battery, crankshaft position sensor, and spark plugs. Intermittent problem, sometimes just cranks and never starts, other times fires right up. When it cranks the rpm gauge does not move at all, tested for spark on one of the spark plugs in the coil pack, none. Don't know what to change next, please help. Coil pack replaced in the past 3 years already. Check engine light on for crankshaft position sensor and crankshaft position sensor.

thanks, Daniel.

 

I'll go out on a limb here and say CPS...

 

Do you ever notice any weirdness with your fuel gauge or voltage gauge when you turn the key on (but not cranking)?

 

Nope, the fuel and voltage gauge looks fine when I turn the computer on. The RPM gauge doesn't register when the problem is occuring. Just replaced the fuel pump, didn't solve the issue. I'm thinking maybe camshaft position sensor, coil pack, relay, or some wire grounding somewhere.

 

Start with my sig, #1. Pretty close to free, just a bit of time and effort, and can solve a host of problems.

See also Cruiser's tips.

Also check your battery terminals and cables. Don't be gentle - corrosion can creep up inside the jacket and do unseen damage.

Next, what brand of CPS did you use? If it was aftermarket, it's a prime suspect. Use only NTK/NGK, the original used by Chrysler. Aftermarket sensors for these things, especially the CPS, have a really bad track record of being bad out of the box, or failing very quickly. As in, weeks, or even days.

 

Your jeep will not produce spark with a bad CPS.

 

What's sig #1? Ya I can spend more time with battery cables and such, but if the starter is getting power, and the computer is getting power, can bad battery connection really cause no spark?
I bought an aftermarket CPS but I believe the previous CPS in there was from Mopar and only like 3 years old and so I don't think that is the problem cause then both the relatively new Mopar sensor, and the brand new aftermarket sensor, would both have to be bad. And this is also only intermittent, usually it starts up just fine. Problem most often occurs when Jeep is driven over 20 min, then left for 1 to 2 hours. If I drive it for 20 min and then start it in 10 min it will always start. If I drive it for 20 min and leave it for 6 hours it will always start.

 

Based on what you describe, the next thing to check would be the ASD relay (in the PDC under the hood). It is commanded by the computer, and once closed will provide the primary ignition system with current. If you hand verify that the ASD relay is operating properly when voltage is applied, then I would start focusing on the CPS again.

My suggested order would be:
1. Clean ground connections (as suggested earlier, and not just the battery)
2. Verify ASD relay for proper function
3. Verify CPS (verifying an intermittent CPS can be challenging - probably will require catching it misbehaving while viewing on a scope).

Starter gets voltage almost directly from the battery. So it can be working fine while other components are failing do to bad electrical connectivity, particularly ground connections. This is especially true if all you have cleaned up is the battery posts and terminals, but not cleaned up any of the other ground connections under the hood in a while.

 

Update: My jeep always starts. Sometimes it still cranks for awhile and I have to turn it off and try again but it always starts. I replaced the Camshaft position sensor and that fixed it. However, I have found the cause of rhythmic clicking in my jeep and it appears to be coming from under the camshaft position sensor, maybe from the synchronizer assembly. I was told by a mechanic awhile ago that it had some play. I'm wondering if all of this is connected. New cam sensor will temporarily fix the problem but the real problem causing the crank no start is a loose camshaft position sensor assembly which is causing a timing issue. Maybe that explains why sometimes it doesn't fire up still but whenever I try again, and the assembly has moved a little and is in sync, it works fine. Thoughts? Thanks guys

 

Wait, did you replace the camshaft position sensor, the crankshaft position sensor, or both?

Camshaft position sensor is in the dis.....wait you have a 2001. Camshaft position sensor is where your distributor would normally be. It's the grey circle thingy in the middle of this picture*:



Crankshaft position sensor is on top of the transmission bellhousing






*That's actually a pic from a 2000 WJ with the 4.0, but I'm confident it's the same. I've never owned an exploding head model so I don't know 100%

 

Wizard, I have replaced both of them. Camshaft sensor seemed to fix the problem but I have a different problem. Clicking coming from the camshaft sensor.