How to know if the reference/speed sensors are broken?

[josh565]

I have been having some issues with getting my 84' 944 to start these past couple of weeks. One night it just gave up starting, it was a very cold and wet night. Since then, I have been trying to pinpoint what is wrong and whatever is going on, it has passed my knowledge of this car.

So When I try to start the car, I can hear the fuel pump so I have a good fuel pump dme.

I have a pressure of 35 psi from the fuel rail, so no fuel issue

I am not getting any spark for some reason, even though I measured the ignition coil and got almost 12 volts from the main terminal. The rotor looked fine, as well as the distributor cap.

Im not getting a tachometer bounce when Im trying to start the engine, which leads me to believe its either the speed or reference sensor.

I channged the oil, oil filter, and gas filter just thinking that a possible tune up may help.

Anywho, how would I go about testing the sensors? Do I pull them out and check for and cracks, or should I take it in to a mechanic who knows what their doing, leaving me to pay a bill?

[911tracker85]

Bad DME or reference/speed sensor?

Josh,
check your other thread link above, I just posted some comments about this.

as I note, you really need an 0-scope to see the crank/speed sensor signals. and when I did mine, I checked at the DME connector to also eliminate the wiring harness.

try the process I and notmyscreenname gave in that thread to see if you are getting toggling of the control lead to the coil.