Porsche Enthusiasts Club Forum

Hi Guys,

Just trying to diagnose a no spark issue with my 944.

I'm getting 11v at the black terminal of the ignition coil which is fine, but the green from the ECU is getting around 6V and dropping to around 4v when turning over. Can anyone confirm if this means the ECU is likely to be at fault i.e for not outputting 12v and pulsing to ground as presumably it should. Are there any other tests i can do to help determine what could be at fault.

I have just temporarily replaced the DME relay with a jumper wire and still no spark so the DME relay isn't the problem.

Checked Injectors and they are pulsing a node light so DME is at least partially running.

Checked RPM and TDC sensors at the DME harness and they are good as are both 12v supplies to the DME.

Still just getting 4-6V at the green wire from DME to the Ignition coil with ignition key on which should be 12V. And not sure if it is pulsing.

And finally, just put an led light on the ignition coil wires and the result is so bizarre:

The light shines brightly with the ignition on and just stays on when i crank the engine.

Does the rev counter bounce when it spins over? If it does it isn't the DME or flywheel sensors.
If it doesn't it means the DME isn't seeing the engine spinning. Generally the crank sensor(s)

The DME earths out the coil to generate a spark. Have you tested the coil, preferably by substitution.

I'll check Tach bounce tomorrow and see on that, thanks.

The strange this is though is that this led bulb is lighting up on ignition when connected to the ignition coil terminals which means somehow the negative (green wire) is grounded. It's showing 6v to ground on the green wire when ignition is on, but also it is managing to light an led.

I have checked the coil OHM readings and all good.I have another coil and will replace tomorrow too, but it feels like the problem is before the coil, (in the DME).

Checked RPM and TDC sensors at the DME harness and they are good as are both 12v supplies to the DME.

not sure they should have a voltage, as they are both Hall effect sensors?

Waylander wrote:Checked RPM and TDC sensors at the DME harness and they are good as are both 12v supplies to the DME.

not sure they should have a voltage, as they are both Hall effect sensors?

Only check to do with them is resistance. From memory around the 800 ohms mark. But check the manual.
Tach bounce is a good way of seeing if the DME is seeing the signals.

Sound like you have an earth issue