Perma-tune CD unit
 

1977 911S Targa. I have bench tested this unit according to the instructions given by Early_S_Man . I get no whixtle and there is no spark when the momentary on switch is pressed. The engine starts instantly and runs for 1 and 1/2 minutes at 3000 rpm. It then gradually slows down and quits within another 30 seconds. As it slows down there is a noticeable miss and some backfiring. I can keep it running a little longer with the acccelerator but not smoothly. I have checked fuel pressure and quantity. I have checked the injectors and replaced one but this didn't make any difference. I had a couple members of our porsche club come up and spend 6 hours checking fuel, timing, the WUR, removed the distributor and cleaned and lubricated it. I have new plugs, new rotor, new distributor cap. Since their visit I have replaced the coil with a MSD PN8222. I have also replaced all the ignition wires, new from Pelican. I have checked the ground connections and nothing seems to make any differerence. We have tried adjusting the fuel distributor with the 3mm allen wrench. I have also installed a new fuel filter. The last thing I can think of is this Perma-tune box. But if it the bench test shows that it is not working why would the engine run at all? What am I missing???

Sounds kind of like a fuel starvation problem.

Did you remove/check/clean the fuel screen in the fuel tank?

yep.. a CIS testing and adjustment gage kit for $75 would diagnose fuel flow.

Big vacuum leak? do you have a pop-off valve? if so, see if it has come loose. If not check the airbox for cracks and all the rubber intake boots, etc.