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
1 answer 1 comment
ANSWER by on 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
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COMMENT by on 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.