Porsche Enthusiasts Club Forum

Hello,

My immobiliser is playing up.

It usually starts no problems but when the engine is warm, sometimes the engine will turn over but not start. I thought there was an electrical problem and today I noticed that when this happens, the boost gauge on the dash, that is supposed to reach 1, to confirm the immobiliser is deactivated...does not do this. When I wave the fob around the ignition key hole...it does make a click noise and the flashing light that also goes out and confirms deactivation, works as it should. Usually, when the immobiliser is active, the car does not turn over at all. although, with this electrical problem (after the car has been running for some time/warm) the starter motor turns over the engine but it does not fire up. So, I'm presuming that part of the immobiliser operates correctly but the other part is not (sometimes)..only after sometime, and when the boost gauge moves to 1, does the engine start - that is how I know it must be a problem with the immobiliser.
If this makes sense to anyone, would appreciate any advice - or I'm going to try and take the whole immobiliser system out as it's very annoying. I was stuck in a car park for an hour today. Although, I have no idea where the immobiliser unit will be and I am guessing I will have to take the dash apart to remove the fob sensor.

Thanks

Katherine.

CK had this issue with his 928 GTS and it was the immobiliser.

Normally behind the floor plate in the passengers foot well or under the passengers seat

I have read:

Boost Pressure Gauge
On the 944 Turbo there is a boost pressure gauge in the lower part of the tachometer. This instrument indicates the pressure in the intake manifold.
With the ignition on and the engine stopped, the indicated pressure corresponds to the ambient air pressure (atmospheric pressure) of approx. 1 bar.
Should an excessively high boost pressure occur as a result of a defect, the fuel supply or the ignition is cut off automatically.

Maybe not the immobiliser then?

Whittling it down:

If the DME/KLR is getting power, the boost gauge in the dash will move up to about 1. If the boost gauge does not go to 1, then you know to look for things that would keep the power from getting to the DME -- relay, alarm, ignition switch, harness, etc.

I have electronically tested the Immobiliser, that is working OK. Next check - DME relay.

Symptoms of a failing DME relay may appear in several ways. Early on, the car may not start or be difficult to start when the engine has been shut down and restart is attempted while the engine is still warm (actually while the DME relay is still warm). When this happens, the car will normally restart when it is allowed to sit and cool for a period of time (usually from 30 minutes up to 2 hours). Another possible failure mode is for the car to suddenly die while driving down the road. Again, the car will often restart after it is allowed to cool.