Zack Coles

For Cold Start/Rough Idle code:

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.

2016 Silverado 1500 5.3L 6-speed RWD. 106K miles. Note: this is a possible root cause based on my towing 300+ every couple of weeks, in addition to heavy cargo. Also, my driving habits may have been on the lugging side. Bought used at 33k, first 30k modest work driving (tolerable cargo, 70-30 highway-city). Symptoms: (After trouble-shooting a poorly mounted injector pump-another post on that) if rpms were below 2500 and I was giving slight more throttle, tach would bounce 100-200 and I could feel a shudder (couple of times heard a grinding/clicking). Never got a code-took to dealership but they wouldn't diagnose it. Was using valvoline atf, did an exchange 20k early, no change. Drove it 6k until i could get to a trans shop (in manual and tow). Diagnosis: Trans pump was failing, possibly because Valvoline never replaced the filter, or just age (and driving). They had to also replace TCC, so final $ was around 5000. Stick with a Tranny shop, have the filter replaced everytime, and stick with the Dextron 6. Also be aware of other codes that may put more strain on the pump.