[hatzie]

I replaced the plugs and wires around the same time as I did the fluids but I didn't comment on it.

NOTE: If the heat shields are rusted away the replacement is ACDELCO 8006 and aftermarket options exist. Mine were fine so I re-used them.

There are supposedly two different coils used on the LQ4 truck engines with differing output terminal position and different length plug wires.

Delphi XS10389 10.5in wires for Coils Stamped 12558693 "Square coil"
Delphi XS10388 9.2in wires for Coils Stamped 19005218 "Round coil"

I use dielectric grease inside the boots on both ends so the wires will actually come off the plugs next time I do them.
The original plugs were the now obsolete AC Delco 41-985 Platinum plugs... Why not use the 41-110 Iridium plugs that are shown as replacements a lot of places?

I wanted to avoid the rumored idling problems and fuel mileage issues that are blamed on the 41-110 plugs.
She idles smooth and gets around 13-14mpg hwy on the new plugs and wires as opposed to the 10-11mpg and slightly rough idle I was getting on the old plugs and wires so I'm happy.

I use Never Seize in the threads. Be exceedingly careful to not get this on the electrodes or past the threaded section of the plugs. I apply it with a plumbers acid brush rather than the slop brush in the bottle to keep it confined to the threads. It's conductive so it'll make trouble if it gets on the ceramic or in the plug boot.

Service bulletin on the spark plugs...

Bulletin Number: 13D-070
Date: May 21, 2013
To: DDG Headquarters and Branches
Category: Product
From: Brad Brunken, Product Development Line(s): 41

Subject: ACDelco Spark Plugs 41-110 and 41-962 - Application Update

Description
ACDelco announces that 2006 and older, as well as some 2007, spark plug service applications
covered by the iridium spark plug 41-110 have moved to the platinum plug 41-962. For the
older model years, GM used a double platinum spark plug in production, and these older
applications are to be serviced with the double platinum plug 41-962. 2007 and newer
applications used iridium plugs in production and service requirements will remain assigned to
the iridium plug 41-110. Both plugs meet original equipment specifications for the applications
designated. Catalog changes for the Epicor and WHI systems will be updated in the June
release 2013. ACDelco recommends you begin adjusting your stocking requirements for the
41-962 in preparation of the upcoming catalog updates. The estimated sales volume split
between the two spark plugs is 50/50 based on these application changes and vehicles in your
markets.