Misfires and visible spark outside rubber plug boot

[John03Z71]

I have an 03 Tahoe Z71 5.3 that has been running a bit rough for quite some time. When I say a bit, I mean a few misses when idling, slight hesitation when accelerating before normal performance, shuddering/shaking randomly on and off when stopped in traffic or at red lights. Enough to be annoying but never bad enough to motivate me to investigate much further (busy work schedule/travel and two young kids = not much free time to tinker around). About 2 weeks ago I had a rare free weekend so I decided to try and solve the problem by changing the plugs and wires, which was overdue (probably been 80k at least).
Immediately afterwards I test drove and noticed horrible performance... it was the same misfiring issue I had before but it was 3x worse. Idling in traffic literally makes my whole body slightly jerk back and forth it shudders so hard. If I stomp on the gas it sounds horrible and is so bogged down.
I checked all connections and all are snug and going to the correct plugs / coils. I even swapped a suspected bad coil (passenger side closest to the firewall) this weekend but no change. Tonight I decided to investigate more and come to find out there is a visible spark that is coming off that plug (rear most passenger side) outside the wire boot. I triple checked for a snug fit and even swapped the wire out with another one but it still does the same thing. Audible snapping sound with visible spark outside the plug boot, and every time it does that the engine dies down significantly. What could this be? Ruled out the coil and wire, and the plug was new 2 weeks ago. I suppose it could be a bad plug but I didn’t have time to swap it out and see if the same thing happened on a different cylinder.
My question to you guys is what does this sound like, a bad plug from the factory or does the visible misfiring spark outside the rubber boot indicate a different issue?

 

[HiHoeSilver]

I have an 03 Tahoe Z71 5.3 that has been running a bit rough for quite some time. When I say a bit, I mean a few misses when idling, slight hesitation when accelerating before normal performance, shuddering/shaking randomly on and off when stopped in traffic or at red lights. Enough to be annoying but never bad enough to motivate me to investigate much further (busy work schedule/travel and two young kids = not much free time to tinker around). About 2 weeks ago I had a rare free weekend so I decided to try and solve the problem by changing the plugs and wires, which was overdue (probably been 80k at least).
Immediately afterwards I test drove and noticed horrible performance... it was the same misfiring issue I had before but it was 3x worse. Idling in traffic literally makes my whole body slightly jerk back and forth it shudders so hard. If I stomp on the gas it sounds horrible and is so bogged down.
I checked all connections and all are snug and going to the correct plugs / coils. I even swapped a suspected bad coil (passenger side closest to the firewall) this weekend but no change. Tonight I decided to investigate more and come to find out there is a visible spark that is coming off that plug (rear most passenger side) outside the wire boot. I triple checked for a snug fit and even swapped the wire out with another one but it still does the same thing. Audible snapping sound with visible spark outside the plug boot, and every time it does that the engine dies down significantly. What could this be? Ruled out the coil and wire, and the plug was new 2 weeks ago. I suppose it could be a bad plug but I didn’t have time to swap it out and see if the same thing happened on a different cylinder.
My question to you guys is what does this sound like, a bad plug from the factory or does the visible misfiring spark outside the rubber boot indicate a different issue?

Crack the plug putting it in? Have you taken it back out to inspect?

 

[ivin74]

Crack the plug putting it in? Have you taken it back out to inspect?

X2, I put money on it

 

[John03Z71]

Crack the plug putting it in? Have you taken it back out to inspect?

No, I have not taken the plug out to inspect it but I can try to do that this evening. The only thing that concerns me is that this problem (snapping sound with simultaneous engine misfiring at idle, and stumbling on acceleration) still existed before I swapped the plugs and wires, it's just much worse now.

I'll pick up a new plug today so if I find its cracked tonight I can pop a new one in. If for some reason the new plug goes in and the problem still continues what would be the next thing to look at considering the new coil pack and have already tried swapping a wire?

 

[SnowDrifter]

Another vote for checking plug. This ignition stuff is insulated to some pretty high voltages. There should be no external spark anywhere

Not sure it would make sense to chase your cool pack. Step back for a moment and consider the problem. You have something causing electricity to seek a different path to ground than the spark gap. And whatever resistance that sees, is less than the resistance of that 0.06" air gap.

There's a breakdown in insulation somewhere. Not sure if it's plug, ****** wires, or material contamination somewhere. But that should give you a start point.

 

[SnowDrifter]

Also, since you never mentioned where the spark is arcing to (engine or firewall) check your engine grounds

 

[iamdub]

You may have had a breach of insulation in the old/worn ignition components, causing the intermittent misfires. Replacing them with new parts that are defective straight outta the box (common with parts store brand parts such as Duralast) or damaged during installation (cracked plug) will cause the same or worse symptoms, just with shinier parts.

 

[John03Z71]

Y’all were right, I just pulled the plug and sure enough it’s cracked all to hell. Popped the new one in and took it for a test drive, now purring smoother than ever. Many thanks to all for your input and suggestions!!

 

[HiHoeSilver]

Y’all were right, I just pulled the plug and sure enough it’s cracked all to hell. Popped the new one in and took it for a test drive, now purring smoother than ever. Many thanks to all for your input and suggestions!!

Bingo. Good work.

 

[mountie]

( New spark plugs)....... ALWAYS check for cracks on the ceramics. Not uncommon.

Some plugs are manufactured by bulk ( China)...... Sold to places like Pep Boys or WalMart.....

There are better places where spark plugs are manufactured / sold to indy parts stores.

I was working at a performance shop ( Guldstrand Corvette Motorsports in Burbank, Ca)... We had a same problem after a full tune up.
The 'Vette had a miss. The plugs were new. We eventually checked plugs. 2 out of the 8 were cracked.

Don't assume a "new" part is a "known good"..... Sometimes they are not.