05RedZ71Sub

I bought my 2013 Sub earlier this year with 32k miles, have 40k now. I sometimes noticed a slight engine stumble at idle and slight oil consumption, maybe a quart at 2-3k miles. Last week suddenly the idle stumble turned to a full misfire. Still drove ok and was able to drive 20 miles home no problem. When I got home the check engine light came on. Checked code and had misfire cylinder 7. Pulled the spark plug out of 7 and it looks messy. Black fouling. Maybe a little oily. Put a new plug in but no improvement. Put the old one back in.

Dropped the truck at the dealer, fortunate for the 5 yr 100k powertrain warranty. Dealer called Tuesday and diagnosed a broken exhaust valve spring in cylinder 7. Replaced it, fully covered under warranty. Truck runs perfect now, maybe even better than before. I think the stumble is improved or gone. I pulled the plug again today and it cleaned itself a bit but I put he new one in since I had it. I've never had a valve spring break before and not sure if it's AFM related. Hope it was a fluke and didn't do damage to the valve or cylinder. Anyone ever see this happen on these engines?

tech2

I have seen collapsed lifters on the afm cylinders but no broken valve springs so far.

05RedZ71Sub

I assumed someone's lease on this truck in January because the end of lease purchase price is really good. I plan on buying it in 6 months but it I have any more problems I can just give it back and move on.