Engine Knock Diagnosis
 

Hello Everyone,

This is my first post! (Sorry if formatting isn't spectacular)

So, I grabbed an agreeably priced 2000 Cherokee 4.0 with 157,000 miles a few months ago as my first project car. I've been a car enthusiast since I can remember but never really turned any wrenches. That all changed when I got the XJ.

So far, I have replaced the ball joints, shocks, tie rod and tie rod ends, rear sway bar links, front and rear sway bar bushings, spark plugs, the battery and terminals, idler pulley bearing, serpentine belt, headlights and harness upgrade, and door checks.

Throughout all of this, the 4.0 has been making a knock / tick noise. It starts right at idle, and maybe lessens by 50% volume once the engine is up to temp. The ticking speeds up with RPM but does not get louder. It is fairly inconsistent and comes and goes, but is there most of the time. So far, I have done the following -

1. Checked flex plate and flex plate bolts, no issues there. Removed serpentine belt and ran it for a minute to make sure it wasn’t a pulley.
2. Seafoam, oil change, Liqui Moly Hydraulic Lifter Additive. Drove for a few weeks, no change in noise.
3. I took it to a shop for an alignment after all the suspension work, and they used a stethoscope and said it sounds top end, likely cylinder 1 or 2.
4. I pulled and inspected the pushrods and rocker arms. Checked for a crack in the head between cylinder 3 and 4. And pulled the exhaust manifold and checked for cracks. No signs of excessive wear or damage. Time to pull the head! I checked for piston slap by trying to tilt each piston in the cylinder, but they seemed solid. Cylinder walls looked smooth.
5. Replaced the lifters for cylinders 1 and 2. I know the "new lifters on an old cam argument" but hey, I'm not a professional...
6. Put her back together all nice and what do you know? It makes exactly the same noise as before. *Proceeds to pull hair out*
7. More seafoam, oil change, and this time I added Restore Engine Restorer Lubricant.

I've been driving it for 5 days and the noise sounds like it did on day 1. Still apparent at startup idle but lessons some once up to temp.

Can anyone identify what the noise is or possible next steps? I'm thinking about dropping the oil pan to inspect the rod bearings and check for any piston skirt fragments in the pan. Other possible causes might be a bad fuel injector? Links to YouTube below -

All comments are greatly appreciated. Thanks in advance!

Could be piston slap or the flexplate bolts, both pretty common.
It sounds a bit more aggressive than the noises coming from my Jeep that I'm hoping is caused by the flexplate bolts.

I ticking sound from my cracked exhaust manifold. Bought and installed new header and ran smooth with no ticking for awhile. Ticking came back which reminded me to re-torque the header and ticking is now gone for good.

Before I replaced the cracked one, we tried welding the cracks and it worked for a short while, but one night when the weather got down to zero degrees and as I was warming up, a loud knocking sound started. Sounded like driving a tractor. Got it home checked it and very large crack from the weld had developed which was the knocking sound.
If no cracks in your manifold then as previously stated check for loose flexplate bolts.

Oh stupid me. I didn't read the rest of your post. Looks like you already checked the exhaust manifold and the flexplate bolts. All I can add at this point is that even if your exhaust manifold has no cracks, but the gasket allows exhaust leak or if your manifold is slightly warped, you would get the tapping sound from the escaping gases.

Could this be the cracked head issue on the 2000? Are you loosing any coolant? Have you pressure checked the cooling system?
At first I thought this would be piston slap, but I don't think so after listening. Not piston slap. Without a closer look offhand it really does sound like a valve train problem. If it was a rod knock it would have torn itself up by now. It just doesnt sound like anything else but valve train.
So you said you replaced lifters on cyl 1 and 2? That was a mistake in itself, if youre going to pull the head, do them all. Next question, when running, does each rocker arm have the same oiling or are some dry and some gushing. I suspect you might have a lifter preload issue, Preload is a critical lifter adjustment that is much discussed in other threads here, It is not enough to simply torque the nuts to spec. It is a falsity that there "is no adjustment

https://cimg5.ibsrv.net/gimg/www.che...cea005a62a.jpg
https://cimg6.ibsrv.net/gimg/www.che...66e4d7272e.jpg

:thumbsup:

I suspect you'll be removing the pan to find the smoking gun (Rod/Main Bearings, Thrust, Pistons/Pins, Timing Chain, Loose Fasteners, Metal in Pan). It sure sounds pretty clear to be a bottom end noise. However, I would start by sending out the oil to Blackstone Laboratories. Make a note stating that you have a knock. They will give you an idea of where it is coming from by the levels of which metals are in the oil, and I would expect to see coolant contamination. Being a 2000 model year, my bet would be coolant in the oil caused by a cracked head. Early detection saves 00-01 4.0L lives, send out your oil boys.

If it was a cracked head you would be losing coolant. Your head should be fine if your coolant level doesn't drop and you have to add....

Mine done same thing took it to my cousin's shop in town he did a thorough once over said it was just a loud injector they all had the correct fuel psi all that jazz. Took it to my brother's so he could take a look at it....same diagnosis. I ended up changing intake gasket that seemed to help :dunno: