Hi,
I am a an owner of a used 1999 Chevy Blazer 4x4 (4 door if this helps).

I know these codes are in the forum topic of DTC codes explained. But am having trouble following them, (sorry not to much of a mechanic).

P1351 and P0440 I have these printed out from Autozone. What are the first things I should test or replace to fix these codes. BTW on the P0440 I have already checked the cap, and the cap seems good.

The engine light does not always come on, sometimes I will start it, and engine light is there, other times I start it engine light is off. Any help would be appreciated.
Thanks

 

The P0440 can result from the gas cap being off, bad gasket on the cap, or a broken/loose/deteriorated hose to the charcoal cannister (behind the driver rear wheel in the fender panel) I had this code after replacing my fuel pump, and it ended up being a bad connection on the tank vent line. I doubt this is your problem though, unless your tank was recently removed.
But, if your cap is OK, it's most likely a vent/vacuum line leak.

The 1351 can be caused by many things (coil, Ignition module, dist. rotor or cap), but the biggest culprit I've learned through experience is bad spark plug wires. IF your wires are original, I'd replace them.

 

Well gas cap is good, I will check in more detail see if the gasket seal on it is still in good condition. As far as the 1351, spark plugs, distributer cap, and wires all have been replaced recently.