Ignition module question

[my70chevelless]

I'm having trouble with my 87 S10 blazer with the 2.8L V6. She will start & run fine until she warms up or I drive it for a while. Then she just dies as if someone turned the key off. When she does this I can not hear the fuel pump prime I Waite about 10 min. & she starts up. Until I drive it a few more miles & she does it all over again. I believe it's the fuel pump going & have replaced the relay the last time she did this I pulled the gas line off & there was no gas coming through the line as I cracked it over.
I called a friend that is a mechanic & he said it was the ignition module. So when she did it again I pulled two spark plug wires off & she was getting a great spark. Which leads me to my question If the ignition module was bad would I have a good spark?. I always thought that if the module was bad I would not have a spark am I wrong about this!. One other thing is it seems to happen faster when I have the lights & heater on I checked the battery & she has 11.94 volts which I believe is low could this be the alternator going as I know the pump needs 12 volts to run?. Thank you for any help.

[old_master]

1) When it quits, remove the top of the air cleaner and have an assistant crank it over. While it's cranking, watch for fuel spray from the injector.

2) If you have spark, the module is working.

3) Battery voltage: with all accessories off and engine at 1500rpm, battery voltage should be 14.2 volts

[jmagerl]

Just because your able to see a spark does not mean your ign module or coil are good. it takes about 10Kvolts to jump 1/2 inch in free air but about 40KV to jump a spark plug in an engine.

My coil went bad and was clearly making 1/2 inch sparks in air but it wasnt strong enough to jump a plug under compression.

[old_master]

Originally Posted by jmagerl

....it takes about 10Kvolts to jump 1/2 inch in free air but about 40KV to jump a spark plug in an engine.....

Your voltage estimates are about right, but transposed. If you watch the firing voltage on an oscilloscope, while the engine is running, it should be around 7kv. However, to jump a 1/2" gap, the coil needs to produce near maximum output which should be around 40kv to 50kv.