1990 4.3 l Sierra

My fathers 1990 GMC Sierra 1500 Pickup Truck 4,3 L runs fine when it is cold but as soon as it warms up it starts running rough then stalls and won't start. There is no spark when it dies. As soon as it cools off it starts back up and runs fine till it warms back up.

Any idea what the problem is?

Thanks in advance

I had a bad ignition module do that but a coil can do it too. use a dwell meter on the coil when it wont start, if it has dwell it should be the coil. No dwell should be the module.

I had a bad ignition module do that but a coil can do it too. use a dwell meter on the coil when it wont start, if it has dwell it should be the coil. No dwell should be the module.

Ok thanks. I don't have a dwell meter but Im sure I can borrow one