PurpleHaze9414

Anyone experience this when coming out of dod mode? My car has this happen... the car is also lagging then surging.... I recently got p0420 code maybe bad cat? I'm hoping not blown head gasket?

crich88848

Sounds like a blown head gasket. White smoke means you're burning water(coolant) typically. Is there any smoke coming out from anywhere under the hood? Are you sure the smoke isn't grey?

PurpleHaze9414

I don't see smoke anywhere else it may be grey it shoots out a plume of smoke when on highway when I go from 4 cyl to 8 cyl mode

crich88848

Grey smoke could mean you're just running lean.

PurpleHaze9414

Possibly the p0420 is lean on bank 1 I'm hoping its a cat n not head gasket even though both are expensive

crich88848

If it was a blown head gasket you would see smoke all the time, especially when your at a stop.

crich88848

I don't know much about the codes and what they mean. Hopefully someone else will chime in and help you out with that. But like I said, if it's only smoking on the highway when you switch from 4cyl to 8cyl it's unlikely to be a head gasket as those usually smoke all the time when bad.

x11 nut

iTrader: (3)

Smoke only when going 4 cyl to 8 cyl mode is indicative of oil pooling on DOD cylinders and getting burned as soon as those cylinders ignite again. That's one of the bulletins on DOD/AFM LS motors - there is a GM service for it, but at home fix is easier/ cheaper = can of SeaFoam or STP equivalent in gas tank, suck a second can thru a vaccum line & watch the smoke show... Then change your oil. Keeping frequent oil changes and PVC oil separator will prevent it from happening again.