Tapping only under acceleration.
 

So just bought the jeep. Fired it up for more than a few minutes today. Motor sounds great at idle. During acceleration it sounds like the old leaded motors on unleaded. Or it's out of time. I'll be tearing into this weekend to find out more just wondering if anyone might have had the same issue before and what it was.

More info needed

Has it been sitting for awhile? bad fuel maybe?

I'm not sure how long it's been sitting. It's possible bad fuel but it idles like a champ. It sounds like a brand new motor at idle. I'm leaning towards cracked rockers or bad lifter. Possible cam lobe.

not sure what else I can tell you. I just picked it up and don't know a lot of back story on it.
like I said it runs like a champ just idling. Upon acceleration it clicks or taps. The harder the acceleration the worse it is.

Model, engine and year would be nice. My crystal ball is cloudy.

haha ya I suppose so. My bad. It's an 01 xj sport. 4.0l. 4x4 auto. I'll be pulling the valve cover today to check rockers and push rods. Saturday I'll be pulling the head and pan and digging deeper.

This is the ZJ (93-98), WJ (99-04), WK (05+) section. Once you get valve covers off, I would ask any additional questions in the XJ section.

Also that year XJ is known for having the 0331 head that cracks. Something to keep in mind and possibly check.

is it possible for a mod to move it over I'm sorry.
I was unaware of the head issue but was planning on checking it.

Well, imagine that! I'm betting its cylinder#4 with a buildup of carbon from the oil vapor from the CCV. I put a new head on my 2000 WJ 4.0 to replace my 0331 that cracked and the rings couldn't handle the improved sealing by the new valves, so I got increased blowby. If I sit and idle for a long time, it will ping until it burns off. It's either that or a cracked piston skirt, especially if it doesn't get better after driving it awhile.

That's my opinion anyway. Sorry to be so anal about knowing what we're talking about, but it's so hard to get guys to state which engine we're working with. In my first post, I was too tired to be doing any diagnosis and I should not have sniped at you. I tend to be a grumpy old man when I'm tired.

no worries my feeling didn't get hurt. I should've posted all that info in the first place. Also should've been in the right section. New to the forum and didn't realize xj wasn't included in this forum.

I pulled the valve cover and all push rods and rockers are good aside from rockers having some wear. Everything is pretty gunked up. Not the worst I've seen but still not great. I'll be pulling the head this Saturday and check for any cracking or carbon build up. I'll pay special attention to #4. If it's cracked I'll just rebuild the whole thing. Is there any location that is prone to cracking in particular? I know my way around a motor but don't know all the little quirks of the 4.0 yet.

In the middle of the head between #3 and #4 cylinder it should say 0331 or TUPY which is the new casting of the 0331 head. When they "Improved" the valve passages in an attempt at better airflow, they created a weak spot in it. Chrysler says any cracking is due to poor maintenance such as overheating, but that's BS. If that was the case, why did they recast them in 02 with more nickel in the metal? Here's a pic of the TUPY head. If you use a strong flashlight and look down the oil filler hole, you should see the markings. That's also where the crack will be. A cracked head will show as coolant in the oil or steam from the tailpipe or both. https://cimg9.ibsrv.net/gimg/www.che...5f77728f81.png

Great info! there is no milk. Also there is no steam aside from normal. If the head is cracked what's a good replacement head.

Okay, you can buy a TUPY head from the dealer or junkyard. I bought a "Clearwater" head from Odessa Cylinder Head in FL. That cost me $455 complete with new valves and springs and shipping both ways, core return. I got it in 3 days because they have a warehouse in NY. You should call them if you're interested because they used to sell direct, but I saw them advertised on e-bay for more money. Shipping weight was 85 lbs whereas return shipping on the old one was 79 lbs. There's no change in the geometry however.

My opinion is don't waste your money on a refurbished head unless it's a TUPY. There are other suppliers but hopefully you won't need one. Actually a 0331 is a ticking time bomb in my opinion. As long as you've got it apart, you might as well upgrade. Just for peace of mind.

Please note that the "Clearwater" head is drilled for 2 temp sensors. One in the thermostat area and one in the top of the head near the rear alongside the valve cover. Make sure the plug is sealed, whichever one you don't use. I got a rude awakening when the rear one started leaking 2 days after I installed it! I thought the head was cracked because IDK it was there!

The problem with these long stroke engines is the piston skirts come out of the bores at the bottom of the stroke. If the fit of the pistons is loose, they tend to rock and cause piston slap until they warm up. In extreme cases, the skirt will fracture and break off.

These are problems that could appear. The vast majority of 4.0s go their entire lives without anything out of the ordinary happening. The 0331 head gave 4.0s a bad reputation and warped heads are a problem for the 4.7 V8.

If you're taking the head off anyway, replace it with the one Dave mentioned. Will save you from doing it twice if it cracks.