Valve noise? pinging?

OK, I have searched and learned one of two two things, a) I suck at searching or b) nobodys worded this right in a thread so I can find it.

Ok I have a 2000 4.0 31' and stock gears. A few months back my engine started making a horrible racket when under an increased load, such as going up hill. It has been getting slightly worse as time goes on as well. It is quiet at idle, and quite when driving flat ground. Im pretty sure it's the valves tapping away insestently. Sometimes if I give it the boot and kick it down so my rpms are higher it quites down some or completely. Any ideas? any more info i should provide?

Thanks all.

I've had the same problem for over a year now. I was convinced that was a sticking lifter, so I tried a couple of things in an effort to avoid a mechanical fix: Marvels Mystery Oil in the crankcase; Atf fluid in the the crank case for about 50 miles before an oil change; Auto Rx cleaning cycle. All did nothing to chang the ticking under load. So, I'm really begining to think it isn't a lifter, but an exhaust manifold leak (i suspect) at the gasket on the head.

I have also heard that loose flexplate bolts could have the same effect.

Well it's defentally sounding top engine side so maybe the exhaust leak. I mean it defentally has the metallic sounding ping of a valve or lifter. but ill poke around there and see if something cant be found.

it sounds like "preignition" which is caused by "higher-than-designed" combustion temperatures. The three usual culprits for this are:

1) extremely lean mixture (vacuum leak allowing too much air or low fuel
pressure/ volume reducing amount of fuel)

2) overly advanced timing ( rarely a concern on the 4.0-- but if the CPS has
been knocked out of it normal position, it's a
possibility)

3) carbon deposits ( carbon in the combustion chamber will restrict the
ability of the cylinder head to transfer heat to the
cooling system and retain localized hot spots that
under load, will get hot enough to fire the fuel/air
mixture before the piston reaches TDC)

A plugged exhaust and crossed/damaged plug wires can also cause this, but they usually have other symptoms that rear their ugly heads at other times as well.
I'd Seafoam it and look for vacuum leaks first, and investigate from there if it continues.

Thanks Shorty, that makes alot of sense, ill bet on 1 or 3 of your above. I have a can of the Mopar brand combustion chamber cleaner in the shed at Mom's ill run it this weekend. Ill also check for vacuum leaks while I am in there. 2 doesnt seem too likely as i dont think i have any reason the CPS would be out of whack.

now that i am thinking on it actually, there is a vacum fed device (sorry for my lack of vacum system workings) on the firewall passenger side that has had an increased noise in it's ticking. Im wondering if this is going bad and causing some vacum issues? which then leads to the issue in #1?

My '99 starting making a noise under load when warm. Turns out my exhaust manifold is cracked. Take a shop vac with the hose on exhaust and get someone to hold it on the exhaust pipe and feel around the bottom part of the manifold - just above where it connects to the crimped pipe. I have a big leak there and at least one more under the intake. I have an APN exhaust manifold on order. This will be my project next weekend.

ok so I ran the combustion chamber cleaner through, and it has quited some but not a whole lot. But now the weird issue, it didnt really smoke out the tail pipe and now it's idling a little rough, any ideas on this new issue??

Oh i should also say, i have used the Mopar cleaner stuff on several other cars including 2 other xj's just not this particular xj before, and i did a 60 mile trip afterwards, other then the at idle issues it runs ok it seems.