I have a 1994 Ranger with the 4.0 5 speed that chatters under load, not so bad with high test 91 octane, horrible with regular 87 octane though. This happens mostly on steep hills.
It has 125,000 on it, changed the oil at 123,000 with no difference. I have had this truck for about six months and it runs good, I would like to fix the chatter. Any ideas or common things to check, I tried a search and came up empty.

Thanks, Jeff

 

Ok so could this be an issue with the rocker arms and push rods? What has me confused is that it mostly gose away with 91 octane gas.

Jeff