[Ryephile]

Originally Posted by travislambert

Here's a HP Tuners VCM scanner file with a little over a second crank time.
(It's from an LT4.)

https://drive.google.com/open?id=0B0...DF2b2ZHVEdCMkk

@ 14.9 seconds, rail pressure ~15 PSI, cranking starts
@ 15.2 seconds, rail pressure ~33 PSI.
@ 15.4 seconds, rail pressure ~61 PSI.
@ 15.6 seconds, rail pressure ~103 PSI.
@ 15.8 seconds, rail pressure ~323 PSI.
@ 15.9 seconds, rail pressure ~538 PSI, first injector pulse
@ ~16.0 seconds, the car starts

I've logged this several times and it's the same sequence every time. The rail needs AT LEAST 500 PSI before the injectors will pulse. Once the injectors pulse the car starts pretty much immediately.

Thank you for posting that. I wonder why the LT1/LT4 HPFP takes so long to get pressure? Very interesting, and very different from other GDI engines in my experience. The fact that it's roughly a half a second at less than the feed pressure from the in-tank low pressure pump is fascinating. It's almost as if the in-tank pump isn't priming. Hmmm.