Recently my 5.3 vortec has been giving me trouble starting after the engine is warm. Starts great first thing in the morning,but after driving for awhile. It starts having issues starting. I'm getting code po446 evap emissions system vent control circuit and po420 catalyst system low efficiency bank one. Was getting po102 mass air flow circuit low input. Replaced mass air flow sensor and that code went away. Have replaced purge valve, crankshaft position sensor,and fuel filter. Still having issues starting when warmed up and has rough idle when it does start( just till I put it in gear). Any help would be appreciated.

 

Can't believe emission issue would cause this other than a plugged cat. With that I'd suspect a misfire code, you might look into the cat.

 

Ricky, did you replace the EVAP purge valve that is behind the throttle body, or the EVAP vent valve which is located up and behind the driver's side rear tire? I ask because you said you got a P0446 code (which is for the VENT valve) and you replaced the Purge valve.

 

I replaced the one behind the throttle body

 

Well, the EVAP purge valve solenoid normally throws a P0443, P0444.or a P0445 code. Since you have a P0446 code, that is for the EVAP vent valve which is located back by the driver's side rear tire. There is a filter inside of the EVAP vent valve that gets full of dirt and then sets the P0446 as a result. The solution is to install the revised EVAP vent valve with a remote filter. The filter is placed up by the top of the transmission and is connected using a length of heater hose. I'm attaching a copy of the TSB from GM.

Not sure if this will remedy the P0420. How are your Oxygen sensors?

 

Old. I have news ones to be installed,just haven't gotten to it yet.

 

most hard starts after a hot soak are related to fuel pressure leakdown into the manifold from the fpr or injectors into the cylinders. it creates a flood like conditions.

 

What is fpr? Fuel pressure regulator?

 

yes...if the fpr has a vacuum line to the intake manifold...check the line for the presence of fuel. if yes replace fpr.

 

Thanks,I'll check that tomorrow