Jeep exhaust melts cat

[Big had]

Posting for a friend. He bought an 86 jeep with a 92 4.0 EFI motor in it. Had all kinds of problems. Had a shop get everything fixed and it runs great now, problem is it runs so hot on the exhaust it melts cats. Any ideas what the issue could be? Shop seems to think the head was milled or something. Not sure if I understand why cats would melt. I get higher compression. The shop is at a loss at this point. Anyone?

 

[greg92jeepxj]

If the cylinder head was milled , that will raise the compression ratio . The combustion pressure has increased and therefore the combustion temperature has increased with it. Sad to say but the cylinder will have to come off and be properly meqsured for its combustion chamber volume so it can be fitted for a head gasket and shim set to get the head spacing and combustion chamber volume back where it should be . Sorry to be the bearer of bad news but that will be the right way to correct this problem. BTW , if this isn't addressed soonest and the jeep is driven in this condition , your likely to burn the exhaust valves and possibly warp or crack the cylinder head !

 

[JPNinPA]

Agree^^
You may also check the fuel pressure and be sure you are delivering enough fuel.

My stock 05 melted the cats in a few years.