RE: 1987 944 S 2.5 16 Valve N/A will not start
 

Yes to both of those questions, but I don't think the O2 signal would prevent the car from starting, would it? Unless the connector for the O2 sensor was an open connection the DMe would think the engine is running lean and put more fuel in the mixture or run a defalt preset between rich and lean which is more likely.

RE: 1987 944 S 2.5 16 Valve N/A will not start
 

Yes the DME should use the defaults based on the info from the AFM. But we know that you have air flow with no leaks, the AFM resistanc changes based on flow, the DME has been replaced, Spark is present, the fuel pressure is good, the injector crkts are good, the hall sensor is good, the alarm is baypassed, the Mech timing is good, the compression is good, so there is only a few things left to check. Either one of the sensors is lying, the injectors were replaced with the wrong part number,the speed sensor plug should have a DG on it, the wiring between the DME computer and one of the sensors is bad, or one of the sensors is causing the DME to go bad. The only place to go from here would be to remove the plug from the DME and check the wiring. Checkeach input from each sensor and check each wire to ground.

RE: 1987 944 S 2.5 16 Valve N/A will not start
 

Yes yout right as thats all thats left. I'll let you know what I find.
Thanks Kinderrich, you've been a great help...