Yep, I second for cleaning the MAF then de-carbonating the engine.
Pretty much, when these things get old and full of carbon they start to ping, bottom line. Not that it’s really hurting anything, since the detonation associated with the 4.0 is normally very, very slight; but detonation also can be EXTREMELY damaging... like a cracked block in a single PING. But for the Ford 4.0 purposes, the ping can pretty much be considered normal and harmless (mechanically wise). The enormous amounts of ping is more annoying then anything.
It is Easier then you think to clean out your upper end. Replace lower intake gasket with FORD replacement only. The Felpro cork gasket is known to cause even MORE problems then your old 200k-mile one.
Decarbonating the engine can be done a few ways
At home mechanic can remove upper and lower intake, and use warm/soapy water with a brush to clean it out. But in reality, you want to use some chemicals to REALLY clean it. Dab a little sea-foam on some steel wool and start SCRUBBIN! It works like magic; your engine will run like magic afterwards too. Just remember to RINSE the engine parts out with warm water when you are done. You do not want any metal shavings from the steel wool sucked into your chambers
Otherwise you can take them to your local machine shop and have them hot-bathed. It cost $20 for me to get that done locally. Remember FORD gaskets for the Lower intake and valve covers. Everything else is safe to use Felpro/Federal Mogul.
But to be honest, if you are going to go this far, you might as well remove the heads and have them milled and cleaned at your local machine shop. My logic is, since detonation is associated with gas being pre-burned, and that the gas on the 4.0 OHV isnt mixing with the air until the heads, then the problem lies in the heads, not the lower intake. Detonation is usually from the gas condensating (Condensation) on the smooth walls of the intake runners, which causes a 'dripping.' Normally you dont want the intake runners to be perfectly smooth for this reason, carbon is the only filling in the roughness of the heads, making them smooth, thus the high amounts of detonation... i dunno, just a thought haha.
The guys I use charged me $130 for the works, heads look BRAND new. $50 for some gaskets, $250 for some delta cam rocker arms and pushrods, your engine will run NEW. The bottom end of the 4.0s are practically still breaking in at 150-200k miles... don’t believe me? Check out this pic...
That’s 200k miles, factory cross hatching...
