Truck vibrates and groans in 4th and 5th at 2700 rpms and above. on 1991 Nissan Pickup (D21)

I just recently replaced my distributor cap and rotor, plugs and wires. Two days ago I noticed that as I drove down the highway that it groaned at 2700 rpms and above. When I got home I checked my plug wires and cap and discovered one of the screws on the cap had loosened and had a gap about 3/16 between cap and distributor. It seemed to take care of it, however I notice that it still groaned a little. I also notice by the feel, sound and sight of the vibration (in the mirror) of the motor that the vibration seems to be cyclical. I have 232000 miles on it so I don't if it is the timing or .... ???. I have no noticeable loss of power whatsoever. Or loss of gas mileage. The engine is a 1991 4 cyl. 2.4L KA-24 4x4 5 speed stick. And am I to understand the 6 cyl have timing belts and the 4 cyl have chains? So might it be timing, fowled plug, bad connection,...???

by in Springfield, MO on October 14, 2009
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1 answer 1 comment
ANSWER by , October 14, 2009
Hello ,, if you did not have the problem before and have it now ,, make sure you check the gap in the plugs ,,( .036) i think is the corrct gap .. make sure all of them are the same ,, this is criticall on this vehichle
COMMENT by , October 16, 2009
Thanks for that response. They weren't gapped properly, however it still ran the same way. But I decided to go back over my installation of the parts. I found one of the new plug wires had been smashed a little and not touching inside the dist. cap very well. It seems to be the issue but I going to take it out for a full test spin in the morning. I hope that is it.