cranks no spark

[beardogg1]

dme relay....one coil makes when key on....other don't make at all when cranking
good grd . no tack when cranking...cant get ohm reading from crank sensors...used last week ran fine...now wont start....when you break gas line when cranking has pressure AT a loss...300 miles from any Porsche repair house 12v at coil no spark

[76FJ55]

If you are not getting spark you likely have lost one of the crank speed or reference sensors. No Tach and the DME not closing the second relay are both indicative of not getting a signal from the crank sensors.

[Rodsrsr]

Wouldn't the relay be the cause? The second coil should close when cranking. The DME relay is the most common culprit.

[76FJ55]

The DME relay will not cause lack of spark as he stated that the first contact is closing with ignition on. the second relay closes to turn on the fuel when the computer sees engine rotation via the crank and reference sensors.

[Rodsrsr]

Oh yeah that's right. Ref/speed sensor probably not sending signal like you said.

[ischmitz]

incorrect - the 2nd stage of the DME relay closes when the sensors see rotation or when the key is in START. Either one by itself makes it close and turn the fuel pump on. However, there is fuel pressure the 2nd stage of the relay did engage during cranking and the fuel pump ran. Conclusion: the DME relay is not root cause.

If one of the crank sensors is bad there won't be spark or fuel pulses ever. If the Ohm reading is in fact infinite then you identified a bad sensor. This is becoming a common failure mechanism as the sensors age.