My grandpa has a 96' Jeep Cherokee 4x4 4.0L. It's been amazingly reliable and the only repairs over the past 7 1/2 years and 35k miles have only been a leaky radiator & water pump, fan clutch, and the rear main seal. Lately it would act like it was running out of gas for just a second, kind of cut out. It would then not start and act as if it had no spark, but it had fuel then it would start the next day. My grandparents next door neighbor is a great mechanic (a good buddy of mine) who we had look at it and it had a check engine light code for a cam position sensor. He took the distributor cap off and the shaft was really wobbly on the distributor which caused the rotor to chew up the cam position sensor. After replacing the distributor and the spark plugs and wires it ran great but then would stumble randomly again and set off another check engine light code - engine misfire. The neighbor mechanic looked at it again and said the timing chain was worn. When turning the crankshaft pulley it would not turn the distributor shaft until the pulley was turned to 19 degrees before TDC (I believe it was before TDC) and had lots of slack. He's in the midst of changing it now, but after taking it apart he said it had LOTS of slack in the chain and the tensioner in there was toast and the teeth on the sprockets were worn down pretty good. The Jeep has always run what I consider as fantastic, tons of power and pretty smooth but it has always had a slight "miss" at idle that's almost unnoticeable unless you're paying attention. After replacing the distributor the miss went away I'd say about 90%. I'm kind of anxious to see how it is with the new timing chain. I'll go by tomorrow and see it. This Jeep was owned by the Arizona Department of Transportation for the first 11 years and nearly on the dot 100k miles of its life, I assume it was well taken care of, it pretty much looks like brand new. I changed the rear main seal and oil pan gasket last December and the engine was absolutely spotless, it looked like it was a brand new crate motor from the underside - really! It's now getting some PPw/PP and a Fram Ultra filter, quite a bit overkill since it only gets maybe 2,500-3k miles per year on it but that's alright. So my question - What would cause the timing chain to wear this early in life? Thanks.