Check engine light on, codes p0300/ p0174/ p0430. low power up hill and at fwy speed,
Dealer suggested doing exhaust back-flow test to check for obstruction (bad cat?)
Does anyone know how many lbs. of back-pressure is normal? it's a 2006 GMC Sierra 6L non turbo.
my test seem to show apx 0-2 psi at idle and 2-4lbs at 2000 rpm higher at higher rpm, maybe 4-5 psi at 2500 rpm.