Changed plugs cap & rotor.Number 7 plug all black and foil looking.Still has stumble and codes 300 & 307 came wright back. notice orange fire not blue or white. Changed coil.Same thing no change.The owner called a another shop.And he said intake pressure valve or burn't valve. Witch I was getting ready to do compression check.The new plug in number 7 was still white. And got 120 psi. All the rest of the plugs was showing signs of firing and 160 to 180 psi. I'm thinking burn't valve. Also smell gas while its running and lots of water out tail pipe and from muffler.Maybe cracked head or gasket
Has a stumble at idle and getting on the gas! codes po 300 & 307. on 1999 Chevrolet Tahoe
by mikeyb4 in Menifee, CA on March 27, 2013
ANSWER by pushrod , March 28, 2013
120 psi should still fire that cylinder! Need to do an injector balance or a leakdown test. May be washed down with gas, smooth out at road speed? Number 7 plug wet when removed?