P0449 Clarification

Beebe · July 16, 2010

I have a 2000 Silverado 1500 4x4 with a 5.3L. My service engine light has been on so I scanned it. I got a P0420 Catalyst system (left cylinder bank), a P0440 EVAP System, and a P0449 EVAP canister vent solenoid valve codes. I went ahead and cleared them started the truck and it ran and the light did not come on. I shut it down and rescanned it. I got a P0449 again. I cleared it again, and went to work and after 15mins the SES light came on. I am assuming it's a P0449 again.

I did some research and it seems this is common and I need to change the vent solenoid. My question is can this cause random missfires at idle? Awhile back I had a friend use his high end scanner and it was showing random missfires on all cylinders, but only at idle. When I drove it I did not get one single missfire for 10mins. I changed the plugs and wires at 100,000 miles, and have 146,000 now. Sometimes you can get bad wires so I replaced them yesterday. I haven't had a chance to scan it with my friends scanner yet.

I have changed the FPR valve also. The truck doesn't seem to run poorly at idle. The RPM's do not jump around or anything. At idle it's about 500-600 RPMs.

Thanks for the help.

redvett · July 17, 2010

If the vent valve is open at idle the engine Will draw fuel vapors in and cause a misfire due to being over rich.

minibike132 · July 17, 2010

If the vent valve is open at idle the engine Will draw fuel vapors in and cause a misfire due to being over rich.

That is incorrect. The engine will not draw in vapor if the vent is open. It will draw if the purge is open. The vent is not causing a miss.

I don't really have a direction to diag the miss other then the normal things that cause a miss. First things first, if you don't feel a miss does it exist? If anything crank or cam related has ever been replaced, or if battery power has ever been removed from the PCM for an extended period of time the crank variation needs to be relearned.