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New Spark Plug Information for the 4.2L I6

123K views 39 replies 28 participants last post by  Morgstevenson 
#1 ·
I was chasing down some plugs for my 02 TB and contacted ACDELCO.

Here's some interesting news I just got from ACDELCO concerning spark plugs for the Trailblazer. ACDELCO spark plugs 41-965 and 41-981 are being replaced by 41-103 (GM 12598004).

I am including the email I sent them and their reply. Know that this information has also been verified by calling their number at 1.800.223.3526.

---
My email to ACDELCO:

Hi,
My vehicle is a 2002 Chevy Trailblazer. In your on-line catalog you show
two spark plugs available for my vehicle - a 41-965 and 41-981. My question
concerns the interchangeability between the two plugs. Is the 41-981
replacing the 41-965? My vehicle came with 41-965 OEM with a .043 gap,
however, you're showing a .049 gap. ACDelco previous had .043 listed for
this plug then they changed it to .049. Which is correct and why the
change? What are the operating characteristics between the two plugs - heat
range, etc? Any and all info you can give between the two plugs would be
greatly appreciated. Thanks, John.
---

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Here is their response:
Thank you for writing ACDelco, John.
We appreciate your e-mail regarding the spark plug for your 2002 Chevrolet
TrailBlazer. Please know the 41-965 and 41-981 spark plugs have been
discontinued.
Be aware the 41-103 Iridium spark plug is the recommended spark plug for
your vehicle. This spark plug should not be deviated from preset gap.
We are sorry that we cannot be of more assistance with this inquiry. If
further assistance is required please call our representatives at
1-800-ACDelco (1-800-223-3526). They are available from Monday through
Friday, from 8 a.m. until 8 p.m. Eastern Time, for your convenience.
Thank you for your interest in ACDelco.
ACDelco Customer Assistance
---

The ACDELCO plug 41-103 is also used on the 2006 Trailblazer. The tech I talk to on the 800 number verified that both 41-965 and 41-981 are being replaced by the new plug and that production has stopped for those numbers. You can still use the previous numbers if the parts are available. I also asked if the 41-981 replaced the 41-965. The tech said yes but could not answer why the gaps had been changed for the 41-965.

*Note that info this is only for the 4.2L I6 engine.

So I guess they've answered by quest for the plug I will be installing in my TB! :D
 
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#5 ·
Sounds like they are going to the iridiums to replace the older 965-981 platinum plugs. Iridium (the metal) is about 1/3 the cost of platinum and performs as well if not better so I suspect that's the reason. Simplifies parts inventory too.

I've been running the 41-981s with the .043 gap they came set at in my 2002 and it runs and idles perfectly. A narrower gap will be a little easier on the coils too. Less voltage needed to jump the gap.
 
#17 ·
I just pulled six off my shelf today, the only gap tool we have includes a measurment for 0.040 and 0.045. Surprisinginly the 0.040 was met with a little more resistance in clearing the gap than I expected. Each plug that I tested was identical in clearing the 0.040.
 
#18 ·
Happy newcomer

Hi

I'm new on the forum, and just had problem with replacement of the spark plugs. I just installed replacements suggested by Canadian Tire Champion platinum ones with poor result: bad idle.... I just read previous post and I am glad i found this site. My part dealer also suggested me the 41-103 and with a .043 gap, as I understand, I should get much better results.

Thanks !
 
#19 ·
I replaced my 41-965's (116,000 miles on them with more to go) with the 41-103's. They were pre-gaped at 0.040, so I simply installed them. The motor ran real bad and triggered the "check engine" light. I took them back and installed Autolite's AP 5263 and gaped them at0.043. The motor ran smooth as silk and the "check engine" light went out after about 10 miles of driving on the Autolites.
 
#20 ·
Maybe that first time with the ACD's a coil wasn't seated down onto the plug, #1 is a little tricky because of the wiring harness holder if you don't unclip it, or you got a defective plug, but regardless of the reason definitely not the usual results with the 41-103 plugs.
 
#23 · (Edited)
Tblazed maybe you are correct about a defective plug or a bad connection to the coil (although I am sure they were all connected properly) and even though AC discontinued the original plug which cost $3 per plug with a $7 per plug I was willing to pay the price. I am very happy with the Autolite AP 5263 platinum plugs. They seam to be more in line with the original plugs and are able to be gaped. As an added bonus they were only $3 per plug. Sometimes it seams to leave well enough alone. Too bad AC discontinued a plug which worked very well.
 
#24 ·
Thanks

Thanks for the info on the 41-103 plugs. I am installing a new set because I recently replaced th eoriginal plugs with a set of E3's and I've gone through 2 coils so far and wiating for my third to be delivered. It seems strange to me that the E3 plugs could be causing a coil to go bad, but I have no other explanation for it as this problem started a week after I installed them and never had a problem before that. Since I can't seem to find anyone that can tell me why I might be burning out coils (for lack of a better term), I'm trying this in the hopes that it fixes the problem. At $9.52 ea. for the Iridium plugs, I hope I didn't just waste the money. BTW... I know the coils are going bad because when I either disconnect the wire from the one causing the problem there's no change in the engine and installing a new one seems to fix the problem for about 8 days or 500 miles. I may have just wasted my money and may be chasing a ghost a here, but I'm not sure what else to try. I will report back in 500 miles and 9 days. Just in case anyone is curious if this fixed the problem or not. Thanks again guys (and Gals)!
 
#25 ·
Thanks for the info on the 41-103 plugs. I am installing a new set because I recently replaced th eoriginal plugs with a set of E3's and I've gone through 2 coils so far and wiating for my third to be delivered. It seems strange to me that the E3 plugs could be causing a coil to go bad, but I have no other explanation for it as this problem started a week after I installed them and never had a problem before that. Since I can't seem to find anyone that can tell me why I might be burning out coils (for lack of a better term), I'm trying this in the hopes that it fixes the problem. At $9.52 ea. for the Iridium plugs, I hope I didn't just waste the money. BTW... I know the coils are going bad because when I either disconnect the wire from the one causing the problem there's no change in the engine and installing a new one seems to fix the problem for about 8 days or 500 miles. I may have just wasted my money and may be chasing a ghost a here, but I'm not sure what else to try. I will report back in 500 miles and 9 days. Just in case anyone is curious if this fixed the problem or not. Thanks again guys (and Gals)!
Are you burning up the coil over the same cylinder each time or different cylinders? It could be faulty wiring to that coil (ie. short, burnt wire, loose connection).
 
#28 ·
iridiums can be gapped. who told you otherwise?

you can't gap them like traditional plugs, you have to be careful. there's only a small dot of iridium on the ground. avoid touching that and you'll be fine. be careful when passing your feeler/wire gauge through. don't force it.
 
#34 ·
Spark Plug & gas mileage

I replaced my plugs with the 103's and had new tires (General HTS) installed at about the same time. Since then my gas mileage has dropped noticably. Per instructions found on this thread, I stayed with the factory gap, they all checked out around .043. My question is, did my mileage decrease due to the smaller gap size (original plugs were .05 I think) or my new tires or both? Could I improve the mileage if I increase the gaps?
 
#35 · (Edited)
I replaced my plugs with the 103's and had new tires (General HTS) installed at about the same time. Since then my gas mileage has dropped noticably. Per instructions found on this thread, I stayed with the factory gap, they all checked out around .043. My question is, did my mileage decrease due to the smaller gap size (original plugs were .05 I think) or my new tires or both? Could I improve the mileage if I increase the gaps?
If the engine is running smoothly and not setting any codes, then all cylinders are firing. I would suspect the new tires have higher rolling resistance. Plus, the weather is getting colder, gas is being formulated for winter months, and tire pressires will be low in the mornings when it's colder. GM spec'd the gap at .050 only on 2002 year models. There were a lot more coil failures on the 2002 models too, back in the beginning. Higher voltage necessary to jump a wider gap putting more stress on the coils I figure. Wider gap will also contribute to more misfires at high RPMs.
 
#37 ·
This is a pretty old thread, but I'll add my story anyway. I bought new plugs for my '02 TB and they were the 41-103 replacement number, but when I asked about the gap the store told me .049". I questioned them again because that was a larger gap than the old 965s were, and it was larger than the new plugs were out of the box. But they double-checked and confirmed .049 so I opened them all up to that. Well the truck's running fine, but I have noticed sometimes slightly slower ignition (cranks a bit longer to start) and no improvement in gas mileage. After reading above posts I called AC Delco cust svc and they told me .043 is the correct gap!!! So I guess I have to go back in and close them back down.:mad:
In case you're wondering, the store that told me the wrong gap? Autozone.
 
#38 ·
Brass feeler gauge

:eek:fftopic: So maybe a little off topic and not of mjor importance. I have a new craftsman feeler gauge. Its the kind that has about 30 different thickness flat blades that you combine to equal whatever thickness you want. I don't trust those coin shaped ones, anyway, 5 of the "blades" on the gauge are made of brass. I assume that they are to be used to protect softer metals from being damaged like brass punch, but what would one need to use the brass ones on? Anyone have any ideas? :confused: Thanks
 
#39 · (Edited)
I was told to never put any gap tool in an iridium plug because the firing tip is is fine it will destroy them so I am extremely careful but I guess the brass would be a little softer and ok if you don't force it in...never had an iridium plug gap off from the factory...ever and I have replaced a lot of them but to each its own I guess!
 
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