1999 Grand Prix can't get running

I have a 1999 grand prix gt. 2 days ago it started running bad and by yesterday it would not start at all. It sounds like it wants to start but
it won't. I have checked the fuel pressure,good. I checked for spark. I also checked the ignition module and coil packs, both good. I replaced the cam and crank sensors. The diagnostics reads "multiple misfire" code p0300. I am at my wits end. Can anyone help
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If you have the right fuel press at the rail (45 psi for a 3.8)and spark it should run, try spraying carb cleaner into the intake, see if it starts.

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I found the problem. The plenum was cracked and filling the intake with coolant.
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I found the problem. The plenum was cracked and filling the intake with coolant. Its running great now.
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