My XJ's been showing an issue lately where if I come out in the mornings or after my 9 hour shift at work, it doesn't want to turn over. MOST of the time it will crank and fire, but its very very slow, and I know something isn't right. However sometimes it doesn't crank at all, I'll put the key in, (hear the beeping for the door being open) turn it and nothing, and for a brief moment I lose all power, no radio, no more beeping. Then I'll give it a minute and it'll very slowly turn over and start. I've replaced the 5 year old Die Hard with a new die hard platinum, and the problem still remains, I had the starter tested at badvanced auto and it checked out good. All of the wiring seems to be in tact and tight. What's keeping me from thinking its the starter is that, when its started and ran, it'll turn over no problem all day. It's when it sits for long periods of time. Here in Northeastern PA its in the low-mid 30's. Any suggestions? It has 101,000 miles on it

 

Try the Poor man's prime, if that fixes it- its your fuel pump. That's turning it on without cranking, letting the fuel pump regain pressure and trying again.

 

Why would the fuel pump cause slow cranking?

 

If it's not turning over well, it isn't a fuel problem.

I'd start by freshening your grounds. Often overlooked and shouldn't be ignored. More on that below.

If grounds check out AFTER they have been freshened and you are still symptomatic, with the key in the ON position, you should have approximately full battery voltage at the starter. Check it with a meter. If you have full voltage, the problem is most likely your starter. Bench testing of starters is not 100% conclusive. If you do NOT have full voltage at the starter, you need to start working your way back into the engine bay to find out why....ie: bad cable leading to starter, connection, etc.
-------------------------------------------------

Grounds can be the root cause of many electrical gremlins. Refreshing grounds is NEVER a bad idea, and the investment of your time in this procedure is always well worth it!

You can't tell much of anything by looking at ground connections!! You must remove, scrape, clean until shiny the cable/wire ends and whatever they bolt to. Be sure to remove all paint from any ground connections.

Start with the one on the back corner of the head, and where it attaches to the firewall, as it deteriorates over time and is an area that makes it susceptible to damage. Best to replace that woven cable with a #4 or #2 gauge cable. You can attach the one end to the intake manifold if you would like.

Next go over to the engine dipstick tube stud. Remove the nut and clean the wire ends and scrape the block until shiny at the stud. Reattach tightly.

If you are so inclined, add at least a #6 cable from the negative terminal of your battery to one of the bolts on your radiator support.

 

TJ, thanks for all of the info! I plan on going over all of that as soon as I can get to my garage, as of right now, I'm locked out, and the Jeep is in there
I do appreciate the advice though. I really do not want to spend $200 on a starter if I don't have to do so.

 

All grounds were gone over and cleaned. I even put new battery terminals on because the old ones were shot. I also stripped new wiring for the terminals, as well as added an extra ground wire going to the radiator support. If the problem persists (can't tell if its fixed or not because it hasn't sat for awhile, will see in the morning) then it must be the starter

 

It's usually the solenoid that fails, rather than the actual starter motor itself. That's not a concrete rule, but it's typical.

A quick test would be to climb under (make SURE it's in park, yes I know it has a neutral safety switch but you can't ever be too careful), with the key turned to "ON", and jump the terminals on the solenoid with a screw driver. Doing this completely bypasses the solenoid, taking it out of the picture. If she cranks up like normal, then you can pretty much guarantee it's the starter solenoid.

If it still has the same problem, it's possible the starter motor is binding up, OR you have a more serious electrical problem.

But I'd start there. It doesn't cost anything to try, it takes less than a minute to test and will give you an immediate answer.