06sierra5.3

iTrader: (7)

My truck started making a "chicking" sound and started getting slightly sluggish. I also noticed some pinging a lot more than usual that lead up to this over a week or two. I never usually have pinging. It sounded like an exhaust leak. I checked everywhere, including header bolts, and found nothing. I though maybe the cat was starting to break down and maybe it was getting a little clogged. Before I could take it in for diag. I got a misfire. It's missing all the time, cold, hot, idle, under load, etc.

I started pulling coil connectors. and found that 90% of the time, there are two that don't make any changes when pulled. All the rest result in a noticeable additional misfire.

My question is, what are the chances of two coils going bad at the same time? Coincidentally, I changed the spark plugs a week or two before this happened. I used Delco plugs, and gapped them correctly. The chicking sound and sluggishness was there before and after the plug change. No evidence of fouling or anything on the old plugs.

I'm assuming changing the coil/wire on those two cylinders will solve the problem, but I don't want to just throw parts at it if there is something else I can check.

06 5.3, 85,000 miles.

Chiphead

iTrader: (2)

Are those two cylinders next to each other? If so, do a compression test to check for blown head gasket between cyls.

The noise could also be valvetrain related. Any engine mods?

gonzo 6.2

iTrader: (8)

plug installing can crack soooo easy and not know it,replace those two with 2 old plugs,give it a try.

gagliano7

Swap coil with a known good coil and see if problem follows coil.