Chicken or Egg (Plug or Coil Pack)

bfairweath

Active Member
I started having problems with misfires on cylinder 3 a couple months ago that I outlined here. My main question with that post was which AC-Delco coil pack to buy. As I mentioned there, I ended up buying a Delphi. Well, it failed about a month later. Had to replace it with a Duralast from Autozone because I needed it fixed right away - couldn't wait for Amazon. Decided to pull the plug before installing the new coil pack. The electrode was nearly gone. Looked like it might have broken off. Gap was about 0.070". Plugs are all 41-103's. Thought the plug may have been the problem all along. Tried just replacing the plug (with a 41-103, of course) and putting the Delphi coil back in. No luck - still misfiring, proving the coil pack was dead. Misfire went away after replacing the plug and installing the Duralast coil pack.

Fast forward to last Friday. Was headed out of town about 120 miles with the cargo area piled up to the roof and pulling two snowmobiles. Starts misfiring again. Luckily, I was close to a relative's house. Stopped there and hooked up Torque (I've learned not to leave the house without Torque and my OBDII transmitter). Misfiring on cylinder 6. Ran to the closest Autozone and got another Duralast coil and spark plug. Electrode was nearly gone - same as the plug on cylinder 3. Replaced both, misfire gone, continued on trip. Was driving home Sunday after a weekend of snowmobiling, starts misfiring again. This time cylinder 4. Got home and replaced the remaining four plugs and coil packs. All six plugs looked about the same as the attached picture. Electrode nearly gone - gap of about 0.070".

Plugs were less than a year old - about 20,000 miles on them. Like I said, they were AC Delco 41-103's. I thought those things were supposed to last for 100,000 miles (the first set I put in did). Defective?

Could the worn out plugs have been causing the coil pack failures? Increased gap increased the voltage requirement for the spark to jump the air gap, resulting in coil pack failures? Chicken or egg - were the plugs killing the coil packs or did I just reach the mean time of failure for OEM coil packs? Truck is an '03 with 198,000 miles.



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littleblazer

Gold Supporter
So I gotta ask... where'd you get the plugs from. A ridiculous gap plus old coils means they're running harder to jump the gap. Theoretically anyway.
 

Mooseman

Moderator
There are fake ACDelco's floating around out there. Check spelling on the metal body. One telltale sign is it says "ASSEMBLEDA" as well as other signs.

 

budwich

Well-Known Member
some thoughts.... first, you aren't doing any "gapping" yourself, right? Next, what are your "mixtures" reading at idle and at speed? Running lean can cause issues with plugs possibly.
 

TequilaWarrior

Well-Known Member
I've heard people recommend replacing coils as well as spark plugs every 100,000 miles. I'm at 220,000 with 4 out of 6 coils still original, though.
 

Mooseman

Moderator
@bfairweath , looking at that pic of the plug, it looks like a fake with that long space between the hex and threads.
 

TequilaWarrior

Well-Known Member
@Mooseman is likely right, every photo I find of 41-103's has a toric shape between the hex and the area above the threads:
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Admittedly, it is entirely possible that they have two body shapes for this plug, but I doubt it. I've checked Summit, Jeg's, and a few legit online chevy parts dealers and they all show a similar shape as the picture above.
The electrode in your photo looks very badly eroded and would lead me to believe that it's in the wrong "heat range" and/or probably not genuine iridium tipped as the iridium (while fragile to contact) does resist erosion due to spark.
I did a quick search for the part number on the plug in your photo and that number does come back as 41-103, but would be meaningless if it's a phony. I also can't tell from your photo the shape of the tip itself. Their should be a very clean and well defined radius shape from the ceramic to the tip of the electrode like the photo above. In your photo the plug appears to have a tapered electrode instead of a radius. Also, I'm 99% sure there should be a little "dot" of iridium on the ground electrode (you can just make it out above the "P" in the photo above) - your plug does not appear to have that - but it could have been blasted off from spark erosion.
One thing I found strange is that there are currently at least two ACDelco part numbers for 41-103 plugs: 12625058 and 12681663, but it's a GM part and god knows what they do with their part numbers. Sometimes I think they concoct new part numbers just to tick us off. I dislike how they "revision" parts as well, but I don't work for them so I don't get a say.

Edit: Looking at your photo some more - there seams to be thermal scarring at the base of the topside ceramic. I don't recall if any of the plugs that I've pulled out of an Atlas ever had that. It's quite striking. By chance, was there any fluid in the plug holes?
 

budwich

Well-Known Member
maybe the answer to "chicken", is that your plugs are failing first causing issues there after (ie. coil). However, from the number of plug failures, that seems to suggest a deeper problem.
 
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bfairweath

Active Member
I got the plugs off Amazon in a deal similar what was in Mooseman's post above - 6 plugs for like $16 - the ones that wore out AND the ones I just put in.

I think there was a small amount of oil in most of the plug wells. I assumed that's where the brown scoring came from. You can see in the picture that the anti-seize is a little "gooey" where the oil ran down the threads as I took it out. However, there was a lot less oil in the plug wells than I've had in the past. This time, there was no oil on the coil pack boots. The last two times I changed plugs (before this time), the entire boot was saturated with oil.

I did open the gap slightly on all the plugs. Spec is 0.043", I believe. They were like 0.030" out of the box.

Budwich asked about my fuel trims. They run very negative, both long term and short term, compensating for a rich condition.

I bet these plugs were fakes. I still have one extra from the set I just bought off Amazon. I'll take a close look at it looking for ASSEMBLEDA. I'll post some pictures.
 

littleblazer

Gold Supporter
I got the plugs off Amazon in a deal similar what was in Mooseman's post above - 6 plugs for like $16 - the ones that wore out AND the ones I just put in.

I think there was a small amount of oil in most of the plug wells. I assumed that's where the brown scoring came from. You can see in the picture that the anti-seize is a little "gooey" where the oil ran down the threads as I took it out. However, there was a lot less oil in the plug wells than I've had in the past. This time, there was no oil on the coil pack boots. The last two times I changed plugs (before this time), the entire boot was saturated with oil.

I did open the gap slightly on all the plugs. Spec is 0.043", I believe. They were like 0.030" out of the box.

Budwich asked about my fuel trims. They run very negative, both long term and short term, compensating for a rich condition.

I bet these plugs were fakes. I still have one extra from the set I just bought off Amazon. I'll take a close look at it looking for ASSEMBLEDA. I'll post some pictures.
Go grab one from advanced and compare. The real deal ones also have dots in the end where the coil pack clips on. That's the easiest one.
 

Sparky

Moderator
I did open the gap slightly on all the plugs. Spec is 0.043", I believe. They were like 0.030" out of the box.
Never ever adjust gap on iridium plugs. It cracks and you have all sorts of problems.

Though if they are fakes then you're set for failures anyway.
 

TequilaWarrior

Well-Known Member
I got the plugs off Amazon in a deal similar what was in Mooseman's post above - 6 plugs for like $16 - the ones that wore out AND the ones I just put in.

I think there was a small amount of oil in most of the plug wells. I assumed that's where the brown scoring came from. You can see in the picture that the anti-seize is a little "gooey" where the oil ran down the threads as I took it out. However, there was a lot less oil in the plug wells than I've had in the past. This time, there was no oil on the coil pack boots. The last two times I changed plugs (before this time), the entire boot was saturated with oil.

I did open the gap slightly on all the plugs. Spec is 0.043", I believe. They were like 0.030" out of the box.

Budwich asked about my fuel trims. They run very negative, both long term and short term, compensating for a rich condition.

I bet these plugs were fakes. I still have one extra from the set I just bought off Amazon. I'll take a close look at it looking for ASSEMBLEDA. I'll post some pictures.
Don't touch the gap! Real 41-103's are shipped already gapped to spec. If the gap is off - either they were seriously mishandled in shipping to the point of bending the ground electrode - which should be exceptionally hard to do, or they're fake. You have to be ridiculously careful checking the gap on this as the iridium is very easy to damage and certainly don't open the gap on these like you would with traditional plugs - you will damage / break off the iridium on the electrodes.

Edit: @Sparky beat me to it.
 
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budwich

Well-Known Member
I think one "root" has potentially been discovered.... gapping. :-( Of course, it does depend on how "gapping" was achieved... as pointed out, the tip is "fragile" and easily damaged if pressured from a "normal gapping tool". There are ways of bending the "ground finger" without impacting the spark tip but as mentioned, most plugs don't need gapping unless some thing happened to them.
There is potentially another one underlying if the trims are "out of whack".
 
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bfairweath

Active Member
I'm not getting a code for rich condition, but Torque shows the LTFT hanging around -12 to -15 while under acceleration. I'm not going to put any effort into finding that until it throws a code (16 year old truck with 200K).

Here is a picture of one of the failed plugs next to a new one from the batch that I just put in (both sets were purchased from the $16 for 6 Amazon deal, but about a year apart). They are slightly different in the area between the hex and the threads. The old one is stamped with "Assembled in the USA from Japan parts." The new one is stamped "Made in Japan."
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I tried to catch the box where it says "Gap to Vehicle Specifications (some exceptions apply)" but it got cut off. Perhaps I damaged the tips by gapping them. I'm pretty sure I gapped the ones that failed (it was a year ago) as well as the ones I just put in. I'm also pretty sure I gapped the first set I put in that lasted 100,000 miles. I was aware of the dangers of gapping a fine wire plug and was careful not to touch the electrode. Every 41-103 that I've purchased has been way tighter than 0.043". Even the single plug I purchased at Autozone two weeks ago was tight. It's not just the Amazon ones.

Are you guys saying it's better to just put them in out of the box with a tight gap than to try to get them to 0.043"?

Think I'm just going to run these plugs for about 10,000 miles and pull of couple of them to see how/if they're wearing. If they seem like they're wearing, I'll replace them all with non-Amazon ones without gapping them. I don't want to start blowing coil packs again (even though the Duralast ones I put in have lifetime warranties).
 

budwich

Well-Known Member
You are our "eyes". If you are saying that your gap "method" does not touch the spark tip, then it is unlikely that "regapping" is an issue. Further, not sure that "thousands" are an issue... yes if you are saying the gap is something like .035 or so but trying to get exactly .043 is probably not worthwhile especially since normally plug gap expand with age / use.

I think you need to look at other reasons for "blown tips".... my understanding is that these are caused by "pre ignition" which can be caused by lean mixtures and / or cylinder "contamination" such that the piston is running "hot" due to build up from "poor burns". Of course, if the units are fake, then that could also be an issue but it is some what suspicious.

you could also do a resistance check across all plug and compare results with a new one(s).
 
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Mooseman

Moderator
It's funny that both came from the same place but are different. The space below the hex, of course, is different and if you look that the ground electrode, the old one is more round and radiused whereas the new one is squarer with a sharper bend.

Maybe the new one is an NGK because it says Made in Japan. Personally, I wouldn't trust such cheap plugs.
 

m.mcmillen

Gold Supporter
I wouldn't use anti seize on the plugs. It can cause the plug not to get a good ground which could be causing some of your coil problems.
 

littleblazer

Gold Supporter
I wouldn't use anti seize on the plugs. It can cause the plug not to get a good ground which could be causing some of your coil problems.
Plus over torqueing among other things.
 

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