944 S2 - Crank but No start diagnosis help please

[Brummiebluenose]

Having had the car off the road for a bit she started briefly (reluctantly and after I changed the DME Relay) and then wouldn't start again - annoyingly on my drive but downhill from my garage.

Engine Cranks but no sign of ignition. I've been through some other threads across various forums, doesn't seem like the coil is getting a 12V supply.

Immobiliser bypassed years ago before I purchased the car.
DME Relay replaced - no change
DME Relay bypassed with jumper lead - no change
No sign of spark
Ignition coil resistance (primary and secondary) correct.
Ignition coil supply no voltage
Fuses test good
Doesn't look like there is tacho bounce.
Speed sensor (only one sensor on an S2) - replaced - no change.

I looked to do a check on pins 47,48 of the DME but the connections seem to be different to the diagrams I have seen (some look unused where on the diagram they have a use) - picture of mine attached.

Is there a different Pin Out diagram that matches what I have?

It feels like the DME is either not reading the speed sensor output or is not sending the signal to energise the coil - is there a wire that might be disconnected under the fuse box that could explain why it started once and then died whilst being moved (I thought I'd just stalled it).

Any help would be much appreciated. If the rain ever eases off (wouldn't be an issue if it was stuck in my garage!) my next step would be to jumper 2 Speed sensor pins feeding DME from the connector although without knowing exactly what pins at the DME end the best I can hope for is to confirm circuit continuity.

 

[VanhireBoys]

If there is no 12v supply to the coil Id look at the ignition switch - I had a similar issue where my coil was breaking down and causing the ignition key to heat up - Now mine is an 87 Turbo but its likely the same idea ... Worth a check anyway

 

[Brummiebluenose]

Thanks - will try and have a look - had initially ruled out the ignition switch as the engine is cranking and the volt needle moves etc when it goes to the position. Foolishly what I haven't checked is that there is 12v going through the ignition fuse. The rain has now stopped but it is dark - so one for Friday.

 

[VanhireBoys]

I disconnected the + side of the coil as this is directly connected to the ignition switch itself - Well it is on mine - If you are getting 12v down from the ignition switch then look at the coil itself - Hard to get motivated to go out in the rain but hopefully you you will get to the bottom of it

 

[scam75]

Clark's Garage is always helpful, guy knew his onions with 944's. No spark trouble shooting here:

Ignition System Troubleshooting

 

[Brummiebluenose]

So I've been trying some more things and rechecking measurement.

Still crank, no start - no spark. We are getting fuel.
At the input to the coil black wire 12v when key is in position 2. Green zero (measured disconnected from the coil)
Ignition coil resistence measured and within tolerance.

Dizzy cap and rotor replaced about 6 months ago as part of a bit of an ignition overhaul as she was hesitating and running rich (injectors also cleaned and AFM refurbished)
Crank sensor replaced.
Ignition control unit replaced.
Alram by passed Pelican Parts Forum. Word of warning if your alarm starts with a 928 don't use Clarks Garage instructions as bridging pins 1 and 4 on the newer version will result in smoke and possibly fire.
DME relay bridged
Alarm Bridge bridged (pins 4 and 5 - part of the bypass procedure).
Ignition relay swapped out with another one that is the same.


All to no effect.

I'm now confident that the ignition switch works although thank you Vanhire Boys as it did make me recheck the black wire which somehow Id measured badly previously.

Whilst looking for info on a different car that I have which is also unwell I stumbled across the "Operation Charm" which has the wiring diagrams (and more) which indicate that the green wire goes to the ICU (left hand behind the headlight) - which I've changed for a new Bosch part. Is it normal for this to be 0 on new cars.

Next step will be a continuity test on the green wire - annoyingly its a bit of a big to get to the clip on the ICU without removing its heatsink.

If anyone knows how the Ignition Control Unit/Module functions that would help