Cold Start/Rough Idle & Low Pressure codes: check injector pump

[Zack Coles]

2016 Silverado 1500 5.3L 6- speed RWD. Approx 105k at failure. See "Shudder: Root Cause (1)..."https ://www.gm-trucks.com/forums/topic/249007-shudder-root-cause-1-at-higher-mileage/ for issues with tach bouncing and shuddering.

Occasionally get cold start code, in L.A. area, usu while in a hilly terrain in early morning. Tried injector cleaner and new spark (at some back-alley shop), seemed to help for 5-7k, but it came back and more frequent. Eventually had a fleet shop look at it, followed GM service guide and checked for coolant leak (none) then replaced injectors- I don't have a lot of downtime, so I wanted to get ahead of this issue. No Cold Start codes but less than 1k later, went into limp mode (Low Fuel Pressure code, I believe), and eventually had to be towed (wouldn't start that day but fired right up the next morning in the shop). Had this truck since 30k, and no notable issues.

Mechanics found that the high-pressure pump (fuel injector pump) was missing a bolt head and there was a gap at the pump mounting. Looking at the bolt, it appears to have been over-torqued (threads near shoulder were wore down), but I haven't had issues for over 70k. Either previous owner had shudder/trans issues and mis-diagnosed as misfire, or bolts are inclined for early failure (lots of rough freeway, like L.A., last 50k). Either way  new gasket and bolts resolved that issue.