1999 chevy blazer not starting

in the distributor is a ignition control module

there are a couple of things to consider here. That code indicates that the O2 sensor behind the cat is not functioning like the engine computer expects-either the cat itself is not functioning properly or you may have an exhaust leak, or the heater circuit in the O2 sensor is faulty. The cat should get up to 600 degrees and it burns unburned fuel before ti gets to the 2ed O2 sensor-if it cannot do this, the CEL comes on and you have a P0420. Before replacing the cat, clear the code and see if it comes back-if it does, you might try first replacing the O2 sensor. If that doesn't work, get a 'oil fouler' spark plug adapter and install the O2 sensor in it, then install both into the exhaust-this 'shields' the tip of the O2 sensor and slows it down, fooling the engine computer into seeing it switching slowly, as it is supposed to do. Your only other choice is to replace the cat, and an aftermarket cat is much less than an OEM unit.

By the way, if you have burnt valves, a P0420 is the least of your worries.

When you go to an auto store and they give sell you spark plugs they should already be gapped to spec. There is no need to adjust the gap. This may be the reason your car will not start. I would try new spark plugs first then wires. Since the vehicle is a 99 it probably could use a tune up (spark plugs, wires, coils, cap, rotor, chassis lube, and transmission fluid check and flush if needed). Also make sure that the engine block ground strap is in good condition and that there is no corrosion covering the ends of the ground strap. The ground strap is typically located near the firewall and is directly attached from the engine block to the frame of the car.

might be a bad catalytic converter or the timing jumped.

Depending on your mileage, there are different things to change. Being that you have a 99, I'd do the following: oil and oil filter, air filter, spark plugs, plug wires, distributor cap and rotor, fuel filter, and rotate your tires. Take a look at your brake pads and replace them if needed. Make sure your tires are around 36 psi at all four corners. Top off your coolant if needed, as well as brake fluid if needed. A tip for you to help out with this - buy a can of a product called Seafoam, and add half the can to your oil. Drive the car about 75-100 miles, and then change the oil and filter. It'll break down sludge and deposits and help the oiling system work better. For preventative care, do this every 5th oil change. Pour the other half into the fuel tank to clean that system.

egr valve stuck open at idle

Test for weak spark when it wont run....my guess is that its the ignition module inside distributer...they heat up and shut off spark,then cool down and work again for a while...good luck..Lee

try messing with the radiator because it is most likely overheating

there is a lttle type of valve filter in the gas line the size of a spark plug, i had same problem.

Have you tested the crank sensor? sounds like no command from PCM to pulse injectors.