1---Make SURE the box has a clean ground. Scrape around the bolt holes, scrape the rear of the box clean around the bolt holes, and use star washers
2-- Remove the ignition system connectors, the ECU, the resistor, the distributor. Work them in/ out to scrub them clean, and to "feel" for how tight they are. Look into them for corrosion.
3--Get yourself a .008" (that's inches not millimeter) feeler, and you should be able to get them at O'Reallys. Check the gap in the distributor reluctor, and examine it carefully for damage, rust, or debri.
4--Take your multimeter on low AC volts, and hook the leads to the distributor connector. Crank the engine---the meter should read about 1V AC
5--Check supply voltage. Clip your meter to coil +, remove the coil high tension wire and ground it. Crank the engine and watch the meter. You should have "same as battery" or AT LEAST 10.5 volts.
6--Check supply voltage "in run." Put the key in "run" engine off. Hook your meter on probe to battery + (or starter relay battery stud) and the other probe on the blue alternator field lead. You are hoping for a VERY low reading the lower the better. More than .3V (three tenths of a volt) means you have a harness voltage drop problem, and therefore low supply voltage
7--Check what you are getting for spark during cranking. You MUST use the key for this and NOT jumper the starter relay, otherwise the resistor bypass circuit will not be engaged.
"Rig" a spark gap, which you can buy or use a good spark plug with the gap pulled out really wide. Crank the engine and see what you have for a spark
IF this is suspect, "wire around" the factory wiring and retest. To do that, clip a lead from the coil POS terminal to the battery or starter relay battery stud.
Now recheck the spark. You can crank either with the key this time, or by jumpering the starter relay. I like to use a grounded probe, IE a clip lead to ground and hooked to a screwdriver, held "in" at the top of the coil. You should get a nice hot blue spark.
