The most common partial failure is heat related. You will be driving along and it will quit. After it cools off, will run again till it warms up and quits again. Otherwise, it usually is dead and won't do anything at anytime.
Carrying a can of keyboard duster and holding it upside down and blasting the module
will get you off the side of the road quicker if it fails due to heat failure!! Just try 20
seconds or so to start and see if it cranks back up. It also works for coils and other
electrical components and even fuel line heat(vapor lock) problems. So keep a half
empty can in your truck and wait 7 minutes instead of waiting an hour for it to cool!!
I super glued a heatsink to the back of mine and ran a intake tube to the distributor
area to get a blast of cold air from the radiator support blowing on to it.