So I recently changed the spark plugs in my rig and I did them one by one to make sure I didn't mix up the wires, and now when the engine is warmed up it randomly makes a puff sound and has a huge loss of power when accelerating from a stop or to get up to speed, it doesn't always do it, but it just randomly does it. What could this be, I'm gonna replace all the plug wires tomorrow to see if thats the issue. trucks a 4 speed(3 speed with a granny gear as 1st) manual if that matters. Also it doesn't do this at all when the engine is cold.

Here is a video of the sound:

 

I have switched out the Crank Case Breather cap and the PCV valve, and have made sure that the wires are plugged tightly into the distributor cap, I'll let y'all know how it works when I take her for a test ride.

 

Quick update, the sound also happens while the engine is cold, I just didn't have it happen before today, I'm gonna replace the spark plug wires, and If that doesn't change anything im gonna buy new plugs, cause with my luck they could be faulty.

 

Also make sure the wires are separated, It sounds like a crossfire. Did you check/replace the cap and rotor?

 

I checked the cap and rotor and its got lots of life left.

 

Thanks lol, I decided to replace all the wires cause they were nasty looking, pulled one off and the connector stayed behind on one of the plugs, and then I found out eventually that I had cylinders 2 and 4 crossed when I switched the plugs, took me setting up the timing all over again one post too far ahead to figure it out though lol. For those Young-ens like me playing with distributors for the first time, PAY ATTENTION to where the lug nut is on the schematic and on your truck it does matter. Runs smoother than ever now and she fires right up.