1999 XJ 4.0L Automatic
So I have been trying to research this all morning so that I can avoid being "that guy". But I have not quite found my same symptom, so it looks like I'm going to be "that guy" lol.
It started last weekend. I drove the XJ to the gas station. Turned it off and went inside. Came back out 5 minutes later and turned the key in the ignition and all I heard was "clunk" (the sound of the starter armature engaging), but it would not crank. It just continued to make this noise anytime I tried to start it (Now this same thing happened 1.5 years ago and I smacked the starter with a hammer and it fired up. So I purchased a new starter and the rest is history). This time around, I did the same thing. I grabbed the hammer and started smacking it while my wife tried to crank it. Still makes the loud clunk every time. So I'm thinking its the starter just like last time. I towed the car home and swapped the starter since it had life time warranty. After installing the new starter, its doing the exact same thing. Loud clunk from the starter armature every time. It sounded eerily similar to a starter trying to start and engine that's locked up. I put a ratchet on on the crank and the engine spins nice and easy. Now the diag begins. It's obviously getting power because its trying to engage every time. Having it in park or neutral makes NO difference. The cables and connections seem ok at this time. I checked battery terminals for corrosion, none found, but I cleaned them anyway. Although I would still need to open up the wiring harness loom the inspect further. I'm at at a little bit of a loss. I don't want to spend a bunch of money just swapping parts, hoping that I nail it. Anyone have any thoughts?
Thanks in advance.

 

Okay, reasonable steps so far. That clunk means it's getting power, yes, but maybe not enough power. Corroded cables or connectors can conduct enough power to fool you into thinking they are fine, but not enough to actually operate a device. Whether it's a starter or a turn signal, there's often a wide gap between voltage enough to make a meter happy, and supplying enough current to operate the device.

Got jumper cables? CAn you make up a temporary jumper for this? If you can get a known good cable to get power to the starter, then try it, you'll known if it's the cable.

Check that - you'll know if its the HOT cable. If your ground cable is flaky, you'll see the same thing.

See my sig, #1.

 

Great, thanks for the response. As I was doing a little more research, I discovered I will have to dig a little deeper into the wiring.

 

so I have this exact problem. I’m thinking of just changing out my main battery cables. Brand new battery as of two days ago. And new starter this morning that just went clank. I haven’t seen if the engine is Stuck yet but I’m planning on it tomorrow. Did you figure out what it was?

 

Look closely at the battery + terminal. Check for corrosion where the 2 red wires go into the molded lead body of the terminal itself. One wire is for the starter cranking feed ONLY and the other is to the PDC for everything else in the truck. It may show you 12v, but not be able to carry the amps necessary to crank the engine.

 

The loud "clunk" is likely the starter solenoid engaging mechanically but not electrically to apply power to the starter motor itself, or the motor brushes are worn or stuck. You can try tapping on the starter body with a small hammer, or screwdriver handle, or chunk of wood.

As the previous post (from a year ago) suggest, make sure your cable connections are clean and tight, and the cables themselves are in good condition.

 

Measuring voltages on either side of the solenoid while cranking should tell you if the cables are rotten, the solenoid is bad, or the starter motor is bad. 20+ year old vehicle, it's not unusual to have rotten battery cables. The local farm-n-home tractor place usually have a good selection at reasonable prices.