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A few weeks ago my 5.3 started misfiring during acceleration or when a load is placed on it.  It idles just fine with no issues.  With 140K miles I decided a complete tune up was in order.  I replaced all plugs, wires and all 8 coils with good quality OEM parts.  The plugs and wires only had 40K on them but I decided to replace them anyways.  After all that it's still misfiring.  The computer hasn't picked up on it as it has not thrown any error codes and the check engine light hasn't come on.  All 8 spark plugs look exactly like this.  The center electrode is almost gone, its now smooth causing the gap to double in size.  They only had 40K on them.  Any ideas what would cause the misfire to continue?  Any ideas as to why my plugs look like this?  Are the problems related?  Appreciate any insight.  

 

 

spark plug (2).jpg

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Mine was intake gaskets. Fuel pressure is something I always check too

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Your motor doesn't call for an iridium plug? 

 

IX-Tip-Horizontal-768x424.png

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My thoughts Grumpy. 

Ac Delco 41162 Iridium OE is what I found. Same plug as my 12.

So why did you not use the right plug fyrestorm?

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Posted (edited)

I just put iridium plugs and its still missing. I used the correct plugs,  My owners manual calls for AC Delco 41-110 and that's what I used.  

Edited by Fyrestorm

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Rock Auto, OReilly's, Advanced, etc are all showing the 41-162 plug as the correct OEM plug.  Wonder why the owners manual shows 41-110

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2 hours ago, Fyrestorm said:

plug.jpg

 

1 hour ago, dsr611 said:

Rock Auto, OReilly's, Advanced, etc are all showing the 41-162 plug as the correct OEM plug.  Wonder why the owners manual shows 41-110

The 41-110 has been replaced by the 41-162.  The Chicoms have been counterfeiting the 41-110s and they are destroying engines left and right.  So if you paid about $20-30 for a set of eight you can nearly guarantee you bought Chicom plugs.

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Someone gave this answer in this thread over on Sliverado Sierra forum.

 

Quote

To finally answer this question, the 41-110 is a NGK plug and the 41-162 is a Denso plug. GM switched vendors, the plugs are basically the same. As a reminder, there is no ACDelco spark plug manufacturing facility.

 

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Can you tell what cylinders are still misfiring? Like with a live data scan tool?

 

I would do a compression test too.

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12 hours ago, Fyrestorm said:

I just put iridium plugs and its still missing. I used the correct plugs,  My owners manual calls for AC Delco 41-110 and that's what I used.  

It takes about 15% misfires for the human senses to 'feel' a misfire. This raises a red flag for me in that the ECU should show a misfire code long before 15% of all ignition cycles have failed. Has me scratching my head.

 

Need a steaming data record while it's doing this. 

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