Hey all.

My stock 04 C5 has had a hard starting issue since I bought it where if it sits for more than a day it cranks for a while before starting.

One thing i noticed doing some logging is that i have no rpm signal until it starts. Neither on the tach or in the scanner. I replaced the crank sensor but am still having the same issue. Any ideas? I was going to check wiring next but was also curious if I should replace/inspect the cam sensor as well.

 

Did you ever figure this out? Looks like it's been a while.

I believe the cam sensor is a fail-safe if the PCM doesn't see a crank signal. If you crank for a while, the PCM will try and use the cam signal to sync the engine. Once the PCM calculates the timing based solely on the cam sensor, it "limps" the engine to life. Once the engine is running at higher RPMs, the crank sensor often wakes up due to the increased voltage or frequency, and your tachometer suddenly jumps to life.

Since you already replaced the crank sensor it kinda sounds like wire harness or low voltage in general while cranking.