dckotwicki

I just moved from a C6 to a C7. During my time with the C6 it always started and roared to life the moment I hit the start button.

With the C7 it takes a few revolutions before the engine lights up.
In the morning, or when the engine has sat idle for several hours, it is at its worst.

It is my understanding that the C7 has direct injection and the C6 did not. Not sure if that might make a difference or not.

Has anyone else noticed this?

Particularly... Is there anyone that has come from the C6 to the C7 noticing a difference in initial start up?

TXArtic

The C7 runs at much higher fuel pressure than the C6 (direct inj), that is why it turns over a few times before firing...has to build pressure in the fuel system. There is a thread Glen e. started that is called "normal things the C7 does" (or something like that), it would be a good read for you.

A "little" vibration at idle is normal too.

JerryU

Normal, it does take slightly longer than my C6. Yes the direct injection requires about 2000 psi pressure to squirt gas into the compressed air in the cylinder. There is a mechanical pump located under the manifold that builds the pressure, which takes time. Have also found when the car has set a few days it may take slightly longer to start.

Harry2

Good information!
I was wondering about my start delay too, coming from a 2010 C6 that started instantly every time [including after the winter hibernation], listening to the engine crank over for a few seconds before starting was a concern. Glad it is considered "normal" for this engine.

Kracka

I love how my C7 sounds when first firing up each morning, especially if I left in it Sport mode the day before. It still doesn't have the racecar roar to life the GTR does though

Glen e

http://forums.corvetteforum.com/c7-g...ette-does.html

Larry/car

Of interest, the stock exhaust also has a louder note first start in the morning. Must have something to do with the four cylinder exhaust valving. The stock exhaust is also louder in track mode, four cylinder valving must cycle full open, the only thing that could change (?) (I am not dreaming).

Bigdog9586

Someone posted how long it took to start at different temps. As it cranks a lot more at cold temps.

Duntov7

From GM TechLink

Extended Cold Crank with Direct Injected Engines
The 4.3L, 5.3L, and 6.2L (RPOs LV3, L83, L86 and LT1) direct injected (DI) engines available on some 2014-2015 Corvette, Silverado 1500, Suburban, Tahoe, Sierra 1500 and Yukon models may have an extended or long crank time during cold ambient air temperatures.
Direct Injection engines may have slightly longer cold crank times than that of port fuel injected engines. Direct Injection systems run at higher pressures and the mechanical pump on the engine must build up the required pressure before the first injection event occurs.

Following are typical DI engine crank times using gasoline:
If the temperature is below -22°F (-30°C), the recommendation is to perform an assisted start (such as with the use of a block heater).
For ethanol fuel, see #PIP5174: Extended Engine Crank Times When Using E85

Start up Coolant Temperature
Crank Time
Above 50°F (10° C)
up to 1.5 seconds

Between 50°F (10°C) and 14°F (-10°C)
up to 2.5 seconds

NSC5

Duntov7,

Thanks for the post on the extended crank times from Techlink. Since gasoline viscosity doesn't present a problem at lower temperatures I presume the extended crank time is due to slower engine cranking speeds at low temperature. The takeaway from this is if your battery is really low in cold weather it will probably die before the engine spins enough times to build up commanded rail pressure. Probably a bigger issue for trucks/SUVs which will be more frequently driven in cold weather.

I noticed this delayed cranking with common rail DI systems when I bought my first DI diesel pickup from GM back in 2001. It was a noticeable change from my previous diesel pickup.

VNAMVET

A bit crooked......