Hard Crank on initial start and rough idle.

Huckleby · July 4, 2021

I have a 2011 GMC Sierra 1500 with the 5.3 liter LC9. Lately I’ve been experiencing at initial start up, a failure to turn over condition. (Like a dead battery) After several attempts to start it will turn over and start almost normally. I do not believe it is voltage or battery related. All connections seem fine. Once started the engine has a rough idle for the intital couple minutes then Smooths out. Occasionally it will throw a P0300 or P0305 code. Once running it starts and run fine. I do notice vapor from the exhaust when it runs rough and a smell that I can only describe as like an electrical burning smell.

CamGTP · July 5, 2021

It almost has to be battery/voltage related if you turn the key and nothing happens or it's very sluggish on the starter motor. And if you are smelling something electrical, how is it not electrical related?

Clean all grounds and battery connections to the battery, body, engine and starter motor. Often times in climates with salt, the corrosion will go up inside the wires that lead to the starter and will need replacement. You may get lucky and it's just a dirty connection at the starter.

The Misfire codes are unrelated to the starting problem. You have other things to look at for the cylinder 5 misfire. Like spark plug or wire. Worst case is that it's internal like lifter problems, low compression etc etc.

Edited July 5, 2021 by CamGTP

Huckleby · July 9, 2021

Update: After a recent episode of failing to turn over I checked the positive battery cable and starter motor and found that both were hot. I figured the starter was causing too much amperage to be drawn from the battery so I replaced the starter. New starter seemed to crank a little slower than normal and within 5 start cycles the truck again did a failure to crank. In the meantime right after one of the successful starts during a rough idle it gave a P0305 code. This, after I had traded coil packs with another cylinder (so I know it’s not the coil pack anyhow). Could cylinder #5 be hydro-locking, causing the failure to crank at times and rough idle on startup? Thoughts?

Huckleby · July 9, 2021

Okay I think I may have a diagnosis. I think I have a fuel injector stuck open on cylinder 5. I recently replaced the intake gaskets and when I went to relieve pressure from the fuel rail, nothing bled out. I think the injector is flooding #5 with fuel causing an occasional hydro lock condition and also a rich mixture at startup. Ordered a set of new injectors this morning. We will soon see!

Edited July 9, 2021 by Huckleby

Huckleby · January 12, 2022

Final Update: I was wrong. I found that my coolant was disappearing internally and upon further investigation found a blown head gasket on #5 cylinder. I tore it down, milled the heads and reassembled with new gaskets and bolts. It is now running strong as ever.