Bad plugs?

[Tazman]

I changed my plugs two months ago because my truck started running rough and the new plugs took care of the issue. Yet I can tell it is starting the same issue again.When I changed them I saw nothing to out of normal especially from an engine with 225k miles on it. No plugs showed signs of burning oil so I thought all was well. Being it has been just two months since they were changed something has to going on for this to happen. I use OEM plugs so they were AC Delco plugs.

[bd]

Check the cap, rotor and wires.  Look for carbon tracking inside the cap and inspect the center of the rotor for pinholes, often accompanied by a whitish ash.  Make sure the wires have suitable continuity and aren't arcing to ground.  Look up inside the boots for greenish discoloration around the terminals.  Check for arcing between the spark plug insulators and ground below the spark plug boots to verify there isn't a cracked ceramic.  Secondary arcing is easily observed in the dark with the engine running - just watch for lightning.

[Tazman]

I pulled the cap and rotor, the tip on the rotor was burnt and one post in the cap had some corrosion on it. Replaced both hoping for the best. It starts better but the stumbling is still there. I will check the wires next.

[Tazman]

Tell me is it common to see the juice traveling from the plugs to the cap?

[bd]

What do you mean?  Elaborate.

[Tazman]

With the engine running I closed the garage door, shut off the lights and grabbed my mirror. I saw what I thought was reflections of an arch but after seeing the same on both sides I stopped and watched. I could see the blue travel through the wires. Pretty cool to see but I still did not find my problem, but I will.

[bd]

St Elmo's fire!!  You saw a coronal discharge - the ionization of atmospheric nitrogen adjacent to the plug wires caused by intense electromagnetic pulses around the wires.  The air must have been somewhat dry.  That's really cool!   

Inspect the terminals inside the boots at both ends of the plug wires for any discoloration (generally greenish or powdery black when there is a problem).  Green is ozone oxidation, black is soot, both from arcing between the wire and its terminal.  If you have an ohmmeter, you can also check the resistance of the wires.

If the wires are in good shape, check the fuel pressure and spray for vacuum leaks.  Pull the vacuum line off the EGR valve to see if the symptoms disappear.

[Tazman]

Yes it is dry, winter in Arizona usually is. The wires are brand new as of Saturday and hope to check for leaks this Saturday.

Thanks for you help!

[roger97338]

St Elmo's fire!!  You saw a coronal discharge - the ionization of atmospheric nitrogen adjacent to the plug wires caused by intense electromagnetic pulses around the wires.

The information you share with us never ceases to amaze me. Thanks bd!

[bd]