ok guys, i've tried to diagnose this but want to hear what you guys think. my truck is a 92 with a 460 on propane. runs pretty good, but has a lifter sounding tick when cruising. if i mat the go pedal the tick goes away, and if i let off the pedal the sound goes away. its only when cruising and it doesn't matter at what speed or rpm. the motor does seem to have a shake at idle, so i did the plugs, cap, and rotor today and nothing changed. number 5 plug did look a bit different, not bad, but not the same as the others. so i pulled the #5 spark plug wire and it seemed to idle the same, put the plug wire back on while running and seemed like there was no change (kinda hard to tell on a v8 vs on a 4 cyl). so i pulled off a random plug wire (with all other wires plugged in properly) and when i re-installed that wire while running the idle did seem to clear up a bit (the #5 plug is firing...i checked that myself while pulling the wire). so next i will do a compression test on all cylinders once the rain stops. but wondering what you guys thought. does this sound like a collapsed lifter, piston slap, i'm pretty certain its not an exhaust leak. the oil is good and topped up too (i know about the 460 oil psi woahs). thanks in advance

 

First you need to check the lifters preload in the cylinder you think it the lifter noise is coming from.

 

i would start by taking the valve cover off that side and either have someone turn the motor over without starting it (unhook the coil) or run it and see if the rocker arms are moving or not (be prepared for a mess though). that way you can see if it is in the valve train or not and then go from there.

Rgds
Mike