Q: How to check or replace the module without removing the distributor for Chevrolet Astro?
A: First, disconnect the tachometer lead (if equipped) at the Distributor, to check a spark at the coil and spark plug wires without removing the distributor. If there is no spark, remove the distributor cap but leave the connector plugged in and take out the Ignition Control Module from the distributor. Then, with the ignition switch turned On, check for voltage at the Ignition Control Module's positive terminal. If you read less than ten volts, there might be a fault in the wire between this terminal and pin "+" of the Ignition Coil or between any of these points and pin 7-3 on an ignition coil's primary circuit to an ignition switch. In case it is ten volts or more check "C" terminal on the Ignition Control Module; if it is less than one volt then there might be a problem with "C" terminal connection between distributor and coil, bad coil or open primary circuit within the coil itself. If it ranges from one to ten volts replace it with a new one and try whether you now have a spark. No spark then possibly there could be problem with ignition coil. Next unplug pick-up coil connector from Ignition Control Module and using your multimeter test between terminals "B" & "C"; turn on your ignition key while observing voltage reading when momentarily connecting test light between battery positive terminal and Ignition Control Module's "P" terminal for five seconds or less. However if there's no drop in voltage check Ignition Control Module ground otherwise replace it with new one. With this accomplished remove test light from Ignition Control Module terminal while checking for sparks at coil wire as it is done so. If there is no flash, then defective Ignition Control Module that should be replaced occurs in such cases but if flashes occur-pickup coils or their connections may have malfunctioned or not have been grounded properly like they should have been grounding wires touching each other as they do inside distributors failing to carry electric current all way through them thus resulting into non-sparking engines that need immediate correction otherwise they would go on as long as some kind of loud noise is produced by starting motor but which can stop at any moment without reaching full speed just like in one situation we faced outside our dad's old store last Sunday evening when everyone thought something terrible had happened since he was almost killed by that roaring engine that failed to start. To replace the Ignition Control Module, start by disconnecting the battery negative terminal, remove the distributor cap and rotor, and then take out both Ignition Control Module attaching screws before finally lifting the Ignition Control Module away from the distributor. Finally, using two electrical leads to it simultaneously but making sure their positions are fixed properly connect this part to the system again. Reinstall the same Ignition Control Module without wiping off the grease from either its face or that of a distributor base because these parts are slippery. On a new Ignition Control Module use silicone grease provided with it on a heat dissipation place where this part rests against a distributor base and on its own surface. Lastly install Ignition Control Module; attach electrical leads back; install distributor rotor and cap; attach battery negative terminal back on its previous position.