Need help with emissions problem on a 1987 silverado 5.7 tbi
 

Hello my truck recently failed the low speed test on both co and hc.
I have replaced the cap,rotor,plugs,wires,and air filter and it is still failing.
Any ideas where to go next?

Try advancing the timing a few degrees and have it re tested.

oxygen sensor, catalytic converter, muffler. check for exhaust leaks, vacuum leaks. maybe even replace gas cap if that hasn't been done for awhile.

The timing is advanced 2 degrees, and the guy at the emissions said it would be failing a different test if it was the cats or exhaust. I checked the three vacuume lines at the throttle body and they seem fine.
I did notice today the there are only 2 lines plugged into the canister, does anyone know where to find a diagram that shows where all the lines from the charcoal canister should run to?