I have seen this caused by the incorrect or improperly gapped spark plugs, which caused the air fuel mixture to finish burning in the exhaust. As Jim mentioned, retarded ignition timing can have the same effect.


John Luttrell
2001 4x4 short cab, 3 inch lift with 33 inch mudders and Powertrax no-slip in the rear


1991 Jeep YJ, 4 inch suspension lift on 33" BFG's