What would cause a constant ticking sound in a Jeep Wrangler engine?

Detonation....Needs to be fixed immediately

It is probably not detonation as stated above, rather a lifter is sticking and needs to be replaced.

Also, the rocker arm bearings can get worn out. As stated above, just replace.

>Both My 4 litre and my old 2.5 litre ticked when cold. As soon as the engine warmed up it went away.

There are two distinct things in these engines that will cause a tick noise and I've had both occur in both engines. Detonation is NOT going to cause a constant tick as you're saying.

1: you have either a sticking lifter or sticking exhaust valve. My 4.0 wrangler does this when it's cold, I've come to the conclusion that it's an exhaust valve because if you give the engine a minute or two to "cool off" at an idle before shutdown, it seems to not tick the next time it's started. This was never a CONSTANT problem, was more intermittent.

2: You have a leaky exhaust manifold gasket. THIS is more likely your tick. I've had this occur on EVERY jeep I've owned. I think this is due to the fact that EVERY jeep I've owned came straight from the factory without nuts on the exhaust manifold studs at the extreme front and rear of the engine. You need to replace the gasket, torque the manifolds properly and install nuts on the nutless studs.

ADDED TO HIS LIST....

3. Worn cam lobe.

4. Crank bearing/seal worn.

5. Pistion walking.

6. dead spark plug

7. bent push rod.

8. bad roter/cap - thus spark plug not dedet.

9. bent connecting rod.

or your timing could also be off.

Or worst thing worst you blew a piston due to your side wall giving away. this is a common problem on older 2.5liters it happens in the number 1 or 4 cylinder mostly due to un-even cooling. Mine happened from a radiator leak that i didn't notice, and my bud's from and air pocket. If your not offroading and or beating it this shouldn't happen.

Whatever it is get it fixed before you need a new enigine.

All jeeps have a light knock but its just from normal rod/value movement.