A Duramax factory fuel system is vacuum-based. The truck relies on a vacuum pull from the tank and not your traditional pump to send fuel to the injection pump. This is the reason many customers will install an aftermarket lift pump to get more fuel at a steady flow to the injection pump. The only way to get a fuel pressure reading on a 2007-2013 Silverado/Sierra Duramax is to have an aftermarket lift pump installed.
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