Problems With My 2003 Gmc Yukon Denali?

[MAXD]

I Have Had A Ton Of Problems With My 2003 Yukon Denali. I Had A Miss Fire On The Number 8 Cylinder And I Did The Following, Checked The Fuel Pressure (56 Lbs), Changed The Coil Pack On That Cylinder , Changed The Wires(msd), Plugs(acdelco Iridium) And Fuel Filter. I Had A Code Pop Up That Was P0308 And After I Changed The Plugs It Changed To P0300. It Still Idles Like It Has A Misfire And At Low Rpm But Once You Start Going It Runs Fine, Like Driving Down The Highway. Any Ideas?

[Frankie]

In some cases, the catalytic converter has gone bad. If you smell a rotten egg smell in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.

[Molson02536]

Originally Posted by Frankie

In some cases, the catalytic converter has gone bad. If you smell a rotten egg smell in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.

Frankie is in the right direction about the engine running Lean when the engine is at idle. Try Cleaning you MAF sensor and make sure your running the correct octane rating your Yukon's engine is suppose to run on. 87 octane unleaded regular gasoline is the recommended fuel used on the 6.0 liter Vortec on the 2003 Denali.