problem happening with my 96 chevy vortec 305, 120 K on it. Not hard or rough miles, mainly hiway. It cranks a few times before it starts,but does start. It seems to run better when cold. It does feel like it does have a miss when idling but not all that noticable. It gets noticeable when running along at 40-50mph, It kind of hesitates when starting from stop sign but not that noticeable. It seems to have plenty of power, will get from stop to 50 fairly quick. Have not noticed any funny engine noises. This gone on for awhile now. Truck seems to shift good with no feel of slipping or slow shifts. This is what was replaced on truck late last year say with in the last 8 mo.I run a injecter cleaner in gas about every 10-15 fill ups. No performance parts added,just a plain ole stock truck.

Dist Cap(Borg Warner), then had to put another one on because(2 mo ago) it ran a bit and starting jumping between two of the electrodes in side of cap, dont remember which ones but they were together on one side of cap, rotor(Borg Warner),wires(omni Plug wires with little resiter symbel and 7mm printed on them is what the mechanic put on),Champion double platinum plugs #7013. Air filter. Also the fuel pump was replaced last year and problem was still there.Thought it might be the catylitic converter but its not acting like my wifes truck did when hers went bad.
It finally had the service engine light come on and the code I got was P0300 which the book that came with the code scanner says Random/Multiple Cylinder Misfire Detected. Any ideas as where i can start looking for the problem because the mechanics around are not able to figure it out.Just hoping has had this type of problem and can give me some advice as to where to start looking. Whats bad about the whole thing is my uncle is GM Service manager and he has no clue. LOL. Thanks for any help and recomendations on where to start looking for problem.

 

You said that there was arcing inside the dist cap. that only happens if there is something foriegn inside there or a crack in cap, I would guess that the miss was still there after the "mechanic" replaced the cap and rotor. If so, get something safe to spray inside dist to dry/clean oil or ????? out of there. I would look really hard at the plug wires. 7mm wires are the lower end wires, so arcing either through a boot to block or through the wire insulator is possible. You said it has a small miss at idle, in the dark, let it idle, maybe even in gear with the tires blocked and the emergency brake applied and observe all the wires paying particular attention to the boots closest to the cyl. heads. If no arc at idle or very little, make sure the truck is'nt going to run You over and give it some throttle just for a few seconds is long enough . the extra load will simulate driving. Also, if You're spark plugs have screw on adapters on the top end, take some pliers that have good grooves to grip and tighten those little adapters really tight, just don't break the spark plug, then make sure there is dielectric grease in the boot coating the plug connection, both ends of plug wires. Vacuum leaks will cause missing and can sometimes be hard to isolate. I suppose if the carbon build up in the intake runners in the heads and the intake manifold is bad enough, that could cause a miss. It always amazes me how much more power an engine will have after cleaning intake man and cyl heads out. Next, I would start checking condition of the engine, compression in each cyl. maybe a valve not seating caused by carbon build up,,,,,,,,,,,,,,,Has any one checked live data stream to see what's going on a little more clearly ? Generally , any and all misses are caused by 1 or more of 3 possible areas. 1. ignition. 2. improper fuel/air 3. lack of engines ability to draw in proper fuel/air charge into each cyl, and/or proper compression of that fuel/air gharge. I hope this helps.