Howdy, had something happen today that I've never seen before, curious if anyone else has had a similar experience. Short version: I had 6 new AC Delco plugs fail with less than an hour of run time. Longer version: I was working on my wife's '48 Chevy sedan delivery with a '76 Chevy 350, it's a stock engine, no crazy mods. A couple months ago I had changed the plugs and wires and there was about 30 minutes of run-time on both, but it wasn't running well. I had time today so I was checking the timing and the engine started missing, I shut it down, made some adjustments and checked connections then fired it back up and it was worse. I shut it down and checked everything again to make sure all my wires were connected correctly, right firing order, etc. and when I restarted it, I could barely keep it running. I felt the p***enger exhaust manifold and it was only warm to the touch, driver's side was hot. Messed around with it some more and I couldn't get it to run at all. I pulled all the plugs, put them back into the wires and laid them across the manifold and cranked it over, and I only got spark off a couple. I went through and checked all the plugs and only two were firing, I checked those 2 plugs on all the wires and they were good. The other 6 wouldn'd fire on any of the wires. Basically, over a period of about 30 minutes today I had 6 of my 8 plugs fail, they were AC Delco R44T Copper core, purchased new and they had less than an hour total run time. I changed them out for a set of new NGK plugs and the engine fired off and ran smooth, no issues. Bad batch? Has anyone seen this before?
@Ryan Skiles By chance did you look in cap & rotor . Also did you move the non firing plugs to the known leads ( spark plug wire) that where firing just to verify each non firing / bag plug? Or ignition firing tester between plug wire & sparkplug .. If you still have the plugs , go to another Vehicle & just hook up one plug @ time to see if fires , make sure you ground plug . I had a issue like 40 years ago 44T where bad around 3,500 rpms like a rev limiter good before & after , took me a while to figure out change plugs no issues after.
Two obvious possibilities, bad plugs or something not often thought of, damage during shipment. It's pretty rare in either case. You might want to contact the maker and see if they want to do a QC on them and have you ship them back (on their dime). Tuneup masters tried to use some eastern Europe sourced TM branded plugs. They didn't last long on the shelf or in cars. I've seen Champions with the porcelain that broke around the center electrode. Tip pointed up, it looked fine. Tip pointed down, the gap was shrouded by the insulator. Both of these were in the 80s, but they stuck with me. AC was usually fine, but I did prefer NGK. Again, this was last century, so changes have almost certainly been made since. Haven't changed many plugs recently.
@Ryan Skiles AC Delco RT44T's are now made in China [so it is a lucky dip] Check the resistance of the plug core, and also check for continuity of the tip to the threaded body [I've heard of plugs with hidden cracks in the porcelain causing shorts. NGK aren't immune t these problems [just less likely] I have an O/T Aussie Falcon SW Barra that runs NGK iridium plugs [which are expensive] I've been chasing my tail on an under load misfire, so I replaced the NGK's for another set and the problem went away. 3000 kms [2000miles] later the misfire was back haunting me. Now "I knew" it wasn't the plugs because they are good for 60000 miles, So I purchased a new set of OEM coil packs. But the misfire still persisted under load. Now me being the "king of cheap" had another Falcon, so I swapped plugs from vehicle to vehicle. The misfire followed the plugs to the other vehicle [I should've done this before buying the coil packs] Anyway I purchase another set of iridium plugs and the problem was solved ............ Or so I thought. Approx 3000 kms later and the misfire was back. Now I was getting pissed off replacing spark plugs at $25.00 each ,so I cheaped out and purchased a set of cheap NGK BKR6e's [$4.50ea] It turns out than Ford used this plug in their turbo Barra engines [so all the voodoo "bone pointing" about burning out the coil packs etc is pure ********] It's been running fine ever since [$27 vs 2 lots of $150]
The two things I have found to be good at killing plugs quickly is too much fuel or too cold plugs. Both scenarios prevents the plugs from getting hot enough to burn off deposits during low power usage (idle/cruising) and eventually the buildup prevents them from making good spark, either by insulating or short circuiting them. In this day and age we also have to consider the possibility of fake parts, the chinese have a habit of putting brand names on their own (usually inferior) copies, so unless you can be sure they were actual AC Delco from some large chain selling that brand you never know. That cheap ebay purchase from some noname seller could be cheap because it's fake parts.
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