i've read every misfiring topic there is but couldn't find any with the similar problem: at low idle and low rpm it runs good but from the moment i go past 2000rpm it starts to drop in rpm so when i do 2500 it jumps from 2500 to 2200 -2300 not always the same amount and not always at the same rate but the higher the rpm the more it does
spark plugs and wiring+distributor cap and rotor.

 

Check your distributor shaft for worn bushings. I had an old BMW that did this, that was the problem.

 

bushings have no play, changed coils, still the same,
forgot to mention this came after the truck didn't want to start, i must have had the fuse blown giving power to the eec since this one didn't get any power, after i put a seperate cable + fuse in going to the eec relay it fired right up,
injectors is not the problem either since i'm running carbed propane (not this install aswell: when i switch back to gas it still has issues)

jumped timing? how do i check on these trucks?

 

It's almost impossible for a 4.9 to jump time, it has a gear-driven camshaft.

 

today wouldn't start and if it would just a few seconds, one time even with a giant bang

changed ICM and pickupcoil starts and runs great just have to set ignition timing (removed the distributor)

 

Hey johny, do you still happen to have the old ICM? Thanks, Peace, Dave.

 

hi, sorry i think it's already gone, cleaned up last month.

 

No worries, thanks anyways. I was hoping you still had it so you could run some ohm tests on it. Thanks, Peace, Dave.