First off, I searched and couldn't find a definitive answer so here goes...

The rig- Completely stock 2000 Cherokee XJ, 4x4, 4.0 with AT, 150k miles. Runs/drives fantastic.

The issue- About a week ago, when I attempted to start the rig it began to crank slow like the battery was low. I checked the battery (new as of 3 months ago) and the alternator and everything checks out ok. So i throw the trickle charger on the battery overnight just to be sure. Start it up the next morning and it still cranked over slow, about 3 revolutions and fired right up.
Well, it has progressively gotten worse! Today when I left work, it BARELY cranked over then fired up! What should I check next? Anybody else run into this issue?
The valve cover is leaking oil at the passenger side back corner, right down onto the starter, so I think that may be part of the issue...

What gives???

 

Id say ground...
Check the NEG wires from teh battery, Disconnect them and clean if you have the time.
Check the back ground strap, mine DISINTEGRATED... The starter relay would click a couple times, then it would turn over.
I replaced it with a 6$ 4ga copper "switch to starter" cable from firewall to a manifold stud. I cleaned the firewall and stud up with a dremel grinding wheel.

 

I agree that freshening all engine grounds is a good first step.

Still happening after that? Get a meter. With the key in the ON position, check voltage directly at the starter. If you have approximately full battery voltage there, the problem is the starter. If you do NOT have approximately full battery voltage, then you are experiencing VOLTAGE DROP, and you have to start working your way back into the engine bay to find out why (ie: bad cable, etc.)

Good luck!

 

If not electrical issue from under hood next up would be fuel pump

 

I had this problem. I replaced my battery cables and ground wires, which helped for a while, but it continued to crank slowly - to the point where it would barely turn over. Battery and alternator checked out fine. Finally, I replaced my starter, and it starts up fine now.

I also had oil leaking from my oil filter adapter onto my starter, which may have been a contributing factor. I'm ordering o-rings for that, next. Yours may also be leaking there.

 

Thanks everybody =) I replaced the starter and its good to go! Now on to the valve cover gasket...