98 Astro van wont start

First, the PO420 can be an O2 sensor that is not working properly. If you have a scanner, at operating temperature, the sensors should be moving between.35 and.55 volts. If they are out of that spec, that is most likely causing the PO420 and not a bad converter. Next, if you have spark and it does not start with starting fluid, you must have a really weak spark at the plugs. The spark should be a hot blue snapping spark. If it is white, orange. It is weak and the vehicle will not run or run really bad. In that case, I ask that you check the condition of all plug wires, the cap again, rotor, and plugs. If they all look good and there are no other codes, check the crank sensor for its condition.

If you have good spark, good fuel pressure and it will not start, make sure the injectors are working. (Based on the no start with starting fluid, this is a last resort). You will need a noid light. Most parts stores will lend them to you. It just plugs into the wiring to the injector. Have a helper crank the engine and you should see the light pulse on and off when it gets power. If there is no power, trace wiring back to the pcm for damaged wires and check the PCM for power to the injectors.

One last thing. If you have good spark, fuel, and it still will not start even with starting fluid, check engine compression and timing.

If you are getting an orange spark, you need to have the coil checked. You need to check the ohms between the negative and positive as well as to the output.