Intermittent Spark won't run.
 

I am working on a 1984 944. It fires when first cranked but will not continue to run. I have injector pulse but the coil fires only once per engine revolution. I have replaced both the crank and cam sensors and installed a known good computer with the same result. I have checked all computer inputs as well as power and grounds. I also have scoped the crank and cam sensors and have a strong signal over 2 volts and proper wave form. I cannot understand why it fires all cylinders when first cranked but then stops. Any help would be greatly appreciated.
Ed

Have you check the air flow meter! These are real simple engines, they need 3 things:air,fuel and fire.Make sure you have fuel pressure and the injectors are actually spraying.Then check the aif flow meter to make sure you are getting the proper reading!Good luck!

Thanks for your response. I have checked all the inputs and all seem correct. The most puzzling part is that it runs for about 2 seconds then stops. I have fuel injector pulse the entire time even after it stops running and I continue cranking. I had a test light hooked up to the positive side of the coil and it stays lit the entire time so it is not losing power but when I hook it up to the negative side it pulses for each cylinder while it runs and then flashes once every engine revolution instead of once for each cylinder. It is almost as if it is losing a signal from the position or speed sensor but I have a scope hooked up to them and there is no loss of signal. Every time you turn the key off and crank it again it does the same thing, runs for a second or 2 then stops firing the coil. I do not know what else the computer looks for to fire the coil besides these sensor inputs. I've been doing this for 35 years and this one is really stumping me.
Ed

It could be the electrical part of the ignition switch,they are cheaply made to start with.Other than that it may be thr computer,If you want my computer guy to test it for you, give me a call. 1-866-944-7883

Replaced ignition switch today, same problem. I did more testing and found something interesting. I removed the wire from the negative side of the coil from the coil and hooked a test light up to it and it continues to flash the entire time you crank the engine, hook it back up to the coil and the engine fires then goes back to the single flash every engine revolution. I installed a new coil thinking there may be a breakdown in the coil internal windings, same problem. If I pull the coil high tension wire off the coil the test coil fires a normal spark continuously! If I plug the coil wire back in, the engine fires and dies again just like before. It's almost as if after the computer sees it run it switches to a different control circuit and then ceases to fire the spark for each cylinder.
Ed

Problem Solved!
The aalrm module was bad grounding the coil. Replaced the module, starts right up!
Ed

Cool beans, that does it alot of times, we even have a diagram on our website that shows how to jump the alarm brain!!